doi.org/10.26434/chemrxiv.12752312.v1
Congener-Specific Partition Properties of Chlorinated ParaffinsEvaluated with COSMOtherm and Gas Chromatographic RetentionIndicesJort Hammer, Hidenori Matsukami, Satoshi Endo
Submitted date: 03/08/2020 • Posted date: 04/08/2020Licence: CC BY-NC-ND 4.0Citation information: Hammer, Jort; Matsukami, Hidenori; Endo, Satoshi (2020): Congener-Specific PartitionProperties of Chlorinated Paraffins Evaluated with COSMOtherm and Gas Chromatographic RetentionIndices. ChemRxiv. Preprint. https://doi.org/10.26434/chemrxiv.12752312.v1
Chlorinated Paraffins (CPs) are high volume production chemicals and have been found in various organismsincluding humans and in environmental samples from remote regions. It is thus of great importance tounderstand the physical-chemical properties of CPs. In this study, gas chromatographic (GC) retentionindexes (RIs) of 26 CP congeners were measured on various polar and nonpolar columns to investigate therelationships between the molecular structure and the partition properties. Retention measurements show thatanalytical standards of individual CPs often contain several stereoisomers. RI values show that chlorinationpattern have a large influence on the polarity of CPs. Single Cl substitutions (-CHCl-, -CH2Cl) generallyincrease polarity of CPs. However, many consecutive -CHCl- units (e.g., 1,2,3,4,5,6-C11Cl6) increase polarityless than expected from the total number of -CHCl- units. Polyparameter linear free energy relationshipdescriptors show that polarity difference between CP congeners can be explained by the H-bond donatingproperties of CPs. RI values of CP congeners were predicted using the quantum chemically based predictiontool COSMOthermX. Predicted RI values correlate well with the experimental data (R2, 0.975–0.995),indicating that COSMOthermX can be used to accurately predict the retention of CP congeners on GCcolumns.
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Congener-specific partition properties of chlorinated paraffins
evaluated with COSMOtherm and gas chromatographic retention
indices
Jort Hammer*, Hidenori Matsukami, Satoshi Endo
National Institute for Environmental Studies (NIES), Center for Health and Environmental Risk
Research, Onogawa 16-2, 305-8506 Tsukuba, Ibaraki, Japan
*Corresponding author
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AbstractChlorinated Paraffins (CPs) are high volume production chemicals and have been found
in various organisms including humans and in environmental samples from remote regions. It is
thus of great importance to understand the physical-chemical properties of CPs. In this study,
gas chromatographic (GC) retention indexes (RIs) of 26 CP congeners were measured on various
polar and nonpolar columns to investigate the relationships between the molecular structure
and the partition properties. Retention measurements show that analytical standards of
individual CPs often contain several stereoisomers. RI values show that chlorination pattern
have a large influence on the polarity of CPs. Single Cl substitutions (-CHCl-, -CH 2Cl) generally
increase polarity of CPs. However, many consecutive -CHCl- units (e.g., 1,2,3,4,5,6-C 11Cl6)
increase polarity less than expected from the total number of -CHCl- units. Polyparameter linear
free energy relationship descriptors show that polarity difference between CP congeners can be
explained by the H-bond donating properties of CPs. RI values of CP congeners were predicted
using the quantum chemically based prediction tool COSMOthermX. Predicted RI values
correlate well with the experimental data (R2, 0.975–0.995), indicating that COSMOthermX can
be used to accurately predict the retention of CP congeners on GC columns.
IntroductionChlorinated Paraffins (CPs) are a group of substances that are applied in various products
as plasticizers, coolants and flame retardants because of their chemical and thermal stability.1
CPs are high-volume production chemicals (>1 million metric tonnes yr-1) and are regularly
released into the environment during production, transportation, and recycling processes and
through leaching and volatilization from landfills.2–4 Short-chain chlorinated paraffins (SCCPs;
C10-C13) are found to be persistent, bioaccumulative and toxic (PBT) to aquatic organisms. In
2017, SCCPs were classified as persistent organic pollutants (POPs) under the Stockholm
Convention and subsequently the production of SCCPs has stopped in the US, Japan, Canada
and Europe, and will soon be restricted in China.5,6 Since the PBT properties of medium-chain
(MCCPs: C14-C17) and long-chain (LCCPs; C18 and longer) chlorinated paraffins are less studied and
a matter of debate, they are currently still being produced and used as alternatives for SCCPs.7
Therefore, the overall world-wide production of CPs still upholds its increasing trend from the
1950s, albeit with a recent shift from SCCPs towards MCCPs and LCCPs.
CP molecules are usually produced by free-radical chlorination of n-alkanes. This
chlorination reaction shows low positional selectivity and produces many congeners and
isomers and does not discriminate between stereoisomers.8 CP mixtures can therefore comprise
thousands of congeners with differing chain lengths and chlorination patterns. Currently, due to
the complexity of CP mixtures and the lack of analytical standards, no analytical methods are
available for the identification of individual congeners in CP mixtures or any samples
contaminated with CPs.9 The large variability in molecular structure suggests that intermolecular
interaction properties also vary substantially. Intermolecular interactions determine the
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partitioning behavior of CPs and need to be understood to describe the environmental fate,
bioaccumulation, and toxicity of CPs. The broad bands of CP signals observed in
chromatographic analysis do suggest that congeners have a range of partition properties.10
The objective of this work is to describe the relationship between structure and
molecular interaction properties of CPs through experimental and quantum chemically based
approaches. Gas chromatography (GC) was used to experimentally investigate the molecular
interaction properties, as the retention time of the analyte on a GC column is directly related to
the molecular interactions between the column coating and the analyte molecule. Different GC
column coatings were selected with a range of polarity to elucidate the polar interaction
properties of CPs. The physico-chemical properties of CP congeners were evaluated by deriving
poly-parameter linear free energy relationship (ppLFER) descriptors from the measured data.
Lastly, retention times were predicted using a quantum chemically based tool, COSMOthermX
(COSMOlogic GmbH & Co. KG). COSMOthermX has previously been used to predict partition
coefficients such as octanol-water partition coefficients for CPs.11,12 Because COSMOthermX
requires only the molecular structure as input parameter, it could be a useful tool to predict the
retention and, more generally, partition properties of CP congeners with diverse structures.
MethodsChemicals
Analytical standards of 2,5,6,9-C10Cl4, 1,2,5,6,9,10-C10Cl6 and 2,3,4,5,6,7,8,9-C10Cl8 were
provided by Dr. Ehrenstorfer GmbH (Augsburg, Germany). Standards of 1,1,1,3-C10Cl4, 1,1,1,3-
C11Cl4, 1,1,1,3-C12Cl4, 1,1,1,3-C13Cl4, 1,1,1,3-C14Cl4, 1,1,1,3,9,10-C10Cl6, 1,1,1,3,10,11-C11Cl6,
1,1,1,3,11,12-C12Cl6, 1,1,1,3,12,13-C13Cl6, 1,1,1,3,8,10,10,10-C10Cl8, 1,1,1,3,9,11,11,11-C11Cl8,
1,1,1,3,10,12,12,12-C12Cl8, 1,1,1,3,11,13,13,13-C13Cl8, 1,1,1,3,12,14,14,14-C14Cl8, 1,2,9,10-C10Cl4,
1,2,10,11-C11Cl4, 1,2,13,14-C14Cl4, 1,2,3,4,5,6-C11Cl6, 4,5,7,8-C11Cl4, 2,3,4,5-C10Cl4 and 2,3,4,5-C12Cl4
were obtained from Chiron AS (Trondheim, Norway). 1,5,5,6,6,10-C10Cl6, which was
commercially available from Cambridge Isotope Laboratories Inc. (Tewksbury, MA, USA), was
donated by Otsuka Pharmaceutical Co., Ltd. (Tokyo, Japan). C16, C18, C20-n-alcohols, a mixture of
C7-40-n-alkanes and a mixture of C4, C6, C8, C10, C12, C14, C16, C18, C20, C22, C24-methyl esters (FAMEs)
were obtained from Sigma-Aldrich Japan (Tokyo, Japan). C8, C10, C12-n-alcohols were obtained
from Tokyo Chemical Industry (Tokyo, Japan). A mixture of polycyclic aromatic hydrocarbons
(PAHs) containing naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene,
anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene,
benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, indeno[1,2,3-cd]pyrene and
benzo[ghi]perylene was obtained from Sigma-Aldrich Japan (Tokyo, Japan). Specifics on purities
and concentrations of the CP analytical standards can be found in Supplementary Table S1.
Columns
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Six GC columns were used for the retention measurements in this study (Table 1). The
GC columns were selected to cover a wide range of polarity based on polarity scales provided by
manufacturers. The SPB-Octyl column is of nonpolar nature and the least polar column in this
study. Its coating consists of poly(50% n-octyl/50% methylsiloxane) and exerts retention mainly
via van der Waals interactions. The polar property of columns HP-5ms, InertCap-17ms and DB-
17ms originates from the presence of phenyl groups in the dimethylsiloxane (HP-5ms and
InertCap-17ms) or silarylene-siloxane polymer (DB-17ms) structure of the column coating.
These columns contain 5% or 50% phenyl groups. Phenyl groups have π electrons that have
weak hydrogen (H)-bond accepting properties. The DB-225ms column, with a coating of 50%
cyanopropylphenyl/50% dimethylsiloxane-equivalent silarylene-siloxane copolymer, contains a
polar nitrile group that acts as a H-bond acceptor. The polar property of the SolGel-WAX column
originates from the ether oxygen atoms in poly(ethylene glycol), which has strong H-bond
accepting properties. All columns had the dimension of 30 m 0.25 mm 0.25 μm.
Retention measurements
A program with linear oven temperature increase was applied on all columns until the
recommended maximum temperature was reached (240-300°C). Helium was used as carrier gas
and a flow rate of 1.2 mL/min was maintained throughout all measurements. Retention
measurements for SPB-Octyl, DB-17ms, DB-225ms, and SolGel-WAX were performed using cool
on-column injections on an Agilent 7890 GC, followed by atmospheric pressure chemical
ionization (APCI) and mass selective detection (Agilent 6530 QTOF-MS) (See Supplementary
Section S2 for the optimization of APCI-QTOF-MS parameters for CPs). An injection volume of 2
μL was used. The on-column injector temperature was kept at the initial oven temperature (60
or 70°C) for 0.1 min and increased with 100°C/min to the maximum oven temperature. The
oven temperature was kept at 60 or 70°C for 0.1 min and increased with 10°C/min to the
maximum temperature shown in Table 1. More details are stated in the Supplementary Section
S2. Retention measurements of SPB-Octyl and SolGel-WAX were also performed on a different
system (7890A/7000A triple quadrupole GC/MS, Agilent Technologies) and HP-5ms and
InertCap-17ms only on this system because of its better availability in our laboratory. On the
triple quadrupole GC/MS system, splitless injection at 250°C and electron ionization (EI) were
used. Peak patterns were similar on both systems, and the retention indices (RIs; see below for
the definition) differed only by 7 on average and 20 in the worst case. In contrast to the EI-MS
detector, the APCI-QTOF-MS method allows for a detection of pseudo-molecular ions and thus
better identification of peaks that belong to the stated CP isomers. Therefore, if the
measurements were done on both systems, data from APCI-QTOF-MS were considered for the
latter discussions. Peak identifications for the EI-MS chromatograms of HP-5ms and InertCap-
17ms were performed by using the APCI-TOF-MS chromatograms of SPB-Octyl and DB-17ms,
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respectively, as reference, because the peak patterns were highly similar (see the results
section).
Table 1. Polymer coating compositions of the GC columns and structures of the surrogate
molecules used in COSMOthermX. The circled parts (red) on the molecular fragments refer to
the groups that were disregarded using the weight string function in COSMOthermX. GC system
Column Coating composition
according to
manufacturer
Manufacturer GC oven
temperature
program
GC system /
Detection
Fragments representing the polymer phase in
COSMOthermX
SPB-Octyl poly(50% n-octy/
50% dimethylsiloxane)Supelco
70 °C (1 min)
10 °C/min
280 °C (10 min)
Agilent 7890 GC /
Agilent 6530 QTOF-
MS
HP-5mspoly(5% diphenyl/
95% dimethylsiloxane)
Agilent
Technologies
70 °C (0.1 min)
10 °C/min
280 °C (10 min)
Agilent 7890A GC/
Agilent 7000A
Triple Quad GC/MS
DB-17mspoly(50% phenyl/
50% dimethylsiloxane)1
Agilent
Technologies
60 °C (1 min)
10 °C/min
300 °C (10 min)
Agilent 7890 GC /
Agilent 6530 QTOF-
MS
InertCap-17mspoly(50% diphenyl/
50% dimethylsiloxane) GL Sciences
70 °C (1 min) 20
°C/min
300 °C (10 min)
Agilent 7890A GC /
Agilent 7000A
Triple Quad GC/MS
DB-225ms
poly(50% cyano-
propylphenyl/ 50%
dimethylsiloxane) 1
Agilent
Technologies
70 °C (0.1 min)
10 °C/min
240 °C (15 min)
Agilent 7890 GC /
Agilent 6530 QTOF-
MS
SolGel-WAX Polyethylene glycolSGE Analytical
Science
70 °C (1 min)
10 °C/min
280 °C (5 min)
Agilent 7890 GC /
Agilent 6530 QTOF-
MS
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1 Silarylene-siloxane copolymer; 2 Instead of 5 and 95% mole fractions, 5.3 and 94.7% was used as the liquid phase composition
for HP-5ms in COSMOthermX since the larger fragment contains not only diphenylsiloxane, but dimethylsiloxane as well.
RIs of CPs, n-alcohols, n-alkylmethyl esters, PAHs and n-alkanes were obtained using the
linear temperature-programmed retention index system (LTPRI). This system is used to establish
retention indices for retention times measured under a program with linear temperature
increase:13,14
1)
where Rti is the retention time of the analyte, Rtx is the retention time of the n-alkane eluting
directly before Rti, Rtx+1 is the retention time of the n-alkane eluting directly after Rti and RIx is
the retention index of the n-alkane that corresponds to Rtx. The retention indices of n-alkanes
are defined as its number of carbon atoms times a hundred.
ppLFER descriptors
ppLFERs are useful in characterizing interaction properties that determine partitioning
behavior of chemicals. ppLFERs are multiple linear regression models that use several solute
descriptors as independent variables for the calculation of partition coefficients.15 The most
frequently used ppLFER for the gas-condensed phase partitioning, established by Abraham et
al,16 has the general form:
log K = c + eE + sS + aA + bB + lL 2)
where log K is the logarithmic partition coefficient. The uppercase letters on the right-hand side
of the equation are the solute descriptors: E, excess molar refraction; S, dipolarity/polarizability
parameter; A, H-bond donating property; B, H-bond accepting property and L, logarithmic
hexadecane-air partition coefficient. The lowercase letters are the system parameters. Each
term quantitatively describes the energetic contribution of a molecular interaction to log K.
Since none of the columns from the current study has H-bond donating properties, the bB term
can be ignored. Solute descriptors S and A are both responsible for the polar interactions of the
chemical: S is related to the surface electrostatic property and is thought to represent polar
interactions that result in part from the partial charge distribution over the molecular surface.17
A reflects more specific interactions resulting from H-bond donating sites of the solute
molecule. The L solute descriptor describes the non-specific van der Waals interactions and also
includes the energy needed for cavity formation.15,18 The eE term also describes the van der
Waals interactions but usually has only minor contributions to log K. For more detailed
explanations of the equation, we refer to refs 13-15.
RI=Rt i−Rt x
Rt x+1−Rt x
×100+RI x
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In this study, temperature-programmed RIs instead of log K are correlated with the
ppLFER descriptors. Because temperature-programmed RI is related but not directly
proportional to log K,19 the use of ppLFER for the RI is an approximation. For a more accurate
investigation, isothermal retention measurements would be better suited, although much more
time-consuming than temperature-programmed measurements, as isothermal measurements
must be performed at many temperatures to cover diverse CP structures. The purpose of using
ppLFERs in the current work is to compare semi-quantitatively the polar interaction properties
of CP congeners with varying structures and not to derive accurate solute descriptors that could
be used for later predictions.
Prediction of RI with COSMOthermX
COSMOthermX software is based on the COSMO-RS theory, which uses quantum
mechanics and statistical thermodynamics calculations to determine the chemical potential of a
solute in solution and can thereby predict partition coefficients. Gas-GC coating (i.e., air-
polymer) partition coefficients were predicted following the method by Goss (2011).20
Molecular structures of CPs, reference compounds and polymer coatings were expressed with
SMILES strings, which were then converted to SDF files. Quantum chemical calculations and
conformer selection were performed using COSMOconfX (version 4.3, COSMOlogic) with
TURBOMOL 7.3, which yield a complete set of relevant conformations with full geometry
optimization in the gas phase and in the conductor reference state. The gas phase energy and
COSMO files of the CPs and reference compounds were then used in the COSMOthermX
software (version 19.04; parameterization: BP_TZVPD_FINE_19) to calculate air-polymer
partition coefficients (Kair-polymer). To represent the molecular structure of polymer coating,
monomers or oligomers of the coating polymer structure provided by the manufacturer were
used. For the quantum chemical calculations performed by COSMOconfX, the end groups of
these monomer or oligomer were end-capped with CH3 groups. The CH3 groups were later
disregarded during COSMOthermX calculations by giving a weighting factor of 0, following the
approach by Goss (2011).20 All these surrogate structures used for coating polymers are shown
in Table 1. The polymer structure of the HP-5ms column consists of 5% diphenylsiloxane and
95% dimethylsiloxane and we represented this structure with a mixture of diphenylsiloxane and
dimethylsiloxane in the respective mole fractions (see Table 1) in the COSMOthermX
calculations. For the SolGel-WAX column, an end-capped trimer of ethylene glycol was used, as
in ref 17.
All calculations in COSMOthermX were performed with the combinatorial term switched
off, as is recommended for polymer by the COSMOthermX user guide.22,23 All conformers
generated by COSMOconfX of the target chemicals were used for the calculation of air-polymer
partition coefficients. However, to reduce calculation times, only the top 5 low-energy
conformers returned by COSMOconfX (_c0 to _c4 suffixes) were selected to represent the
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polymer phases. For some CPs, COSMOconfX returned conformers with R or S configurations
that were inconsistent with the input structure. This problem did not occur when we turned off
RDKit and only used Balloon for the generation initial conformers on the Windows version of
COSMOconfX.
For each chemical and coating phase, Kair-polymer was predicted at 5 temperature steps
between 373.15 and 573.15 K. Then, linear regression between log Kair-polymer and 1/T was
established, and a hypothetical eluting temperature was interpolated at a column-specific,
characteristic Kair-polymer value that is derived from experimental data. This eluting temperature
was considered analogous to the retention time and used to derive RI, following eq 2. A more
detailed explanation about how RI values were predicted from COSMOthermX calculations is
presented in the Supplementary Section S1.
Because the stereometric structure of the isomers present in the CP standards is
unknown, partition coefficients were calculated for all possible diastereomers using
COSMOthermX. A pair of enantiomers was represented by a single structure in the
COSMOthermX calculation, because partition coefficients of enantiomers are the same in
isotropic phases. The predictability of the COSMOthermX program was tested by comparing the
mean of predicted RIs for all possible diastereomers and the weighted mean of the measured RI
values of the CP standards from the GC system. RI values of PAHs were calculated but not used
in testing the predictability of COSMOthermX, as their predicted RI values were systematically
deviated from the measured values (see Supplementary Table S4).
Results and discussionDetermination of GC retention times and RI
Retention measurements showed the presence of multiple peaks in most of the CP
analytical standards. Generally, CP congeners with a high number of possible diastereomers
given their molecular structure showed multiple peaks with a substantial peak area of the same
(pseudo)molecular ion. For example, on the SPB-Octyl column, 10 peaks within a minute of
retention time were found for 1,2,3,4,5,6-C11Cl6, which has 10 possible diastereomers (a pair of
enantiomers are considered one structure). In contrast, 1,1,1,3,9,10-C10Cl6 (2 possible
diastereomers) only showed one peak (Supplementary Fig. S1A and S1B). For one standard,
2,5,6,9-C10Cl4 (6 possible diastereomers), the manufacturer-provided certificate of analysis
stated the presence of three diastereomers without details on the exact stereometric structure
(e.g., S and R notation). While we indeed observed three peaks on the nonpolar SPB-Octyl
column, 7 peaks were found on the most polar SolGel-WAX column (Fig. 1), showing increased
separation through polar interactions. As exceptional cases, 1,2,5,6,9,10-C10Cl6 (6 possible
diastereomers) only showed one peak on all columns (Supplementary Fig. S1C) and
2,3,4,5,6,7,8,9-C10Cl8 (72 possible diastereomers) showed 3 peaks on the SPB-Octyl column, and
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only 1 peak on the SolGel-WAX (Supplementary Fig. S1D). These standards likely contain a
limited number of diastereomers. Some CP standards with only few or no possible
diastereomers resulted in a higher number of peaks. For example, 1,1,1,3-C10Cl4 (no
diastereomer) showed 5 peaks over 3 minutes of retention time on the SPB-Octyl column
(Supplementary Fig. S1E) and 4 peaks over 5 minutes of retention time on the SolGel-WAX
column. Most of the peaks in these chromatograms were small and are likely constitutional
isomers (i.e., impurities).
Figure 1. The Chromatogram of 2,3,6,9-C10Cl4 measured on the SolGel-WAX column. The
manufacturer-provided certificate of analysis of this analytical standard stated the presence of
three diastereomers.
As a representative RI value for a CP congener with multiple peaks, the mean of the RI
values weighted by the peak areas was calculated and used in the following discussions. While
we are aware that peak areas do not always reflect the relative abundance of CP isomers
present,24 this approach deemed better than simply calculating the mean of RIs for all peaks
without weighting, particularly in cases where one or a few major peaks appear with many
small peaks.
We note that no retention times of 1,1,1,3,11,12-C12Cl6, 1,1,1,3,9,10,10,10-C10Cl8 and
1,5,5,6,6,10-C10Cl6 could be determined on the SolGel-WAX column, as their peaks were broad
and the response was low (Supplementary Fig. S1F). This peak broadening is probably because
of thermal degradation, as a high temperature (280°C) was needed to elute these congeners.
Indeed, 1,5,5,6,6,10-C10Cl6 and 1,1,1,3,9,10,10,10-C10Cl8 were detected on the other highly polar
column DB-225ms, for which a lower temperature (240°C) for elution was applied.
Comparison of RIs on polar and nonpolar columns
Since polar compounds are retained more by polar coatings, comparing RI values
between columns of different polarity allows for the characterization of the polar interaction
properties of CP molecules and substructures. RIs of CPs on polar columns were always higher
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than those on the nonpolar SPB-Octyl column, showing the significance of polar interaction
properties for all CP standards (Fig. 2). The range of RIs (or separation of
diastereomer/constitutional isomer peaks) for each CP standard was usually greater on polar
columns, meaning that the isomers are better separated with polar retention mechanisms
instead of van der Waals interactions only.
A series of CP congeners with -CH2- increments show that RI on all columns increased
with 102 to 119 per addition of -CH2- to the alkyl chain. These values are similar to the RI values
of n-alcohols (102–107 per methylene) and n-alkylmethyl esters (100–105 per methylene, see
Supplementary Fig. S2).
Chlorine substitution on the alkyl chain generally increased RI to an extent depending on
the column polarity and the position of Cl. For example, the RI of 1,2,9,10-C10Cl4 on the SPB-
Octyl column is greater by 229 than that of a constitutional isomer 1,1,1,3-C10Cl4. The retention
on the SPB-Octyl column is driven by van der Waals interactions, which are correlated to the
molecular surface area of the molecule.25 The four Cl atoms of 1,2,9,10-C10Cl4 are distributed
over the alkyl chain and increase the molecular surface area more than the four Cl atoms of
1,1,1,3-C10Cl4 that are shifted on one side.
Figure 2B shows ΔRI, defined as the RI of a column subtracted by the RI of SPB-Octyl to
clarify the contributions of polar interactions to the retention. Larger ΔRI values are observed
with increasing column polarity, while the trends of ΔRI over different congeners are similar for
all columns. Generally, a single Cl substitution on -CH2- to -CHCl- increases the polarity of CPs.
However, actual contributions appear to depend strongly on the neighboring structure of the
-CHCl- group. A vicinal substitution pattern (-CHCl-CHCl-) does not increase the polarity so much
as an isolated -CHCl-. This is clearly shown with 2,3,4,5,6,7,8,9-C10Cl8, which shows only an
intermediate ΔRI although having the highest number of -CHCl- units. In a vicinal substitution
pattern, the proximity of -CHCl- groups might interfere with, and lower, the polarity and/or H-
bond properties of a neighboring -CHCl- group. In contrast, a single Cl substitution on a terminal
carbon (-CH3) is less influenced by Cl on the neighboring carbon. Comparison of the 5
tetrachloro (Cl4) congeners is illustrative for these trends: 2,5,6,9-C10Cl4 (2 isolated Cl and a pair
of vicinal Cl) and 1,2,9,10-C10Cl4 (2 pairs of vicinal Cl at the ends) show the highest ΔRI, followed
by 4,5,7,8- C11Cl4 (2 pairs of vicinal Cl) and 2,3,4,5-C10Cl4 (4 consecutive, vicinal Cl). 1,1,1,3-C10Cl4
is the least polar of the measured CPs even though it contains one isolated -CHCl- group. This
shows that CCl3 has a much smaller contribution to polarity than 3 -CHCl-. It is interesting to
note that ΔRI of 1,1,1,3-C10Cl4 is about half that of 1,1,1,3,9,10,10,10-C10Cl8. As the latter has
double the CCl3-CH2-CHCl- substitution pattern, this observation suggests that the additivity
principle may hold for the polarity of CPs, provided that the two structural units are far enough
apart. The highest ΔRI was observed for 1,2,5,6,9,10-C10Cl6 (3 pairs of vicinal Cl, of which 2 pairs
at the ends). 1,5,5,6,6,10-C10Cl6 is the only CP standard with double chlorinated carbons and
shows the second highest ΔRI. Comparison to 1,2,5,6,9,10-C10Cl6 suggests that -CCl2-CCl2- may
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be less polar than 4 chlorines all as vicinal -CHCl- groups. Overall, the total number of -CHCl-
groups is not decisive for the polarity of CPs and the chlorination pattern needs to be
considered.
Figure 2. The measured RI on GC columns (A), the measured RIs subtracted by the measured RI
on the SPB-Octyl column (ΔRI) (B), and RI values predicted by COSMOthermX subtracted by
predicted RI values of the SPB-Octyl column (C) for a selection of CP standards. The compounds
are ordered according to the ΔRI for DB-225ms (polar column with data available for most CPs).
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The vertical error bars in panels A and B show the range of measured RIs for multiple peaks,
while the vertical error bars in panel C show the range of predicted RI values for CPs with
multiple diastereomers. Corrections were applied to predicted RIs (see text).
Describing polarity using ppLFERs
To investigate the types and the extent of polar interactions with CPs, ppLFER solute
descriptors were derived. The A and S descriptors describe the polarity of the CPs relevant for
GC retention times. First, the E values of CPs were obtained using the structure based
estimation method from the UFZ-LSER database,26 because E has been considered a simple
additive property.16 The E values obtained are presented in Supplementary Table S3a. Second, L
values were determined from SPB-Octyl data. The SPB-Octyl column exerts minimal polar
interactions, and system parameters s and a were therefore set to 0. Thus,
RI = c + eE + lL 3)
Here, the measured RI values and the solute descriptors (E, L) of n-alcohols, n-alkylmethyl
esters, n-alkanes and PAHs (Table 2b) were used to calibrate system parameters (c, e, l) for SPB-
Octyl by least-square multiple linear regression. The result is given in Supplementary Table S2.
The solute descriptors for these chemicals were obtained from the UFZ-LSER database.26 Then,
from the system parameters and E and RI values of CPs, L values were calculated
(Supplementary Table S3a):
L = (RI – c – eE)/l 4)
The A and S solute descriptors of CPs were calculated from the rest of the data. The
ppLFER model fit the calibration data well with R2 of 0.995-0.997 and the standard deviation
(SD) of 36-59. System parameters for all columns were qualitatively in good agreement with
those reported by Poole et al. using isothermal measurements (Supplementary Table S2). The a
and s system parameters are in the order of the expected polarity of the columns: SPB-Octyl <
HP-5ms << DB-17ms < InertCap-17ms << DB-225ms < SolGel-WAX. The ppLFER equations for the
columns were transformed into:
RI – c – eE – lL = sS + aA 5)
S and A were determined from multiple linear regression with 0 intercept. The results are given
in Supplementary Fig. S3. The standard errors of S and A were relatively high. This can be
because of the incompatible results for the two most polar columns, DB-225ms and SolGel-
WAX. As the e, a and s system parameters of the SolGel-WAX column are higher than those of
the DB-225ms column, one would expect that RIs on the SolGel-WAX column would also be
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higher for all CPs. However, as Fig. 2 shows, RIs for SolGel-WAX were just as much as or even
lower than those for DB-225ms. These conflicting results may cause a relatively large error in A
and S.
As an attempt, we obtained A and S with the RI data for all but the SolGel-WAX column
and for all but the DB-225ms column. While the resulting A and S descriptor values differ (on
average 0.40 and 0.16, respectively), the trend across CP congeners remains the same between
the two approaches (Fig. 3). The S descriptor generally increased with the number of
chlorinated carbons. The lowest values were found for 1,1,1,3-C10Cl4 and highest for
1,2,5,6,9,10-C10Cl6 and 2,3,4,5,6,7,8,9-C10Cl8 (Fig. 3 and Supplementary Table S2). The A solute
descriptor values were not related to the number of chlorines but rather to specific chlorination
patterns. Substructures -CH2Cl and -CHCl- tend to increase A, but with the striking exception
that compounds with consecutive -CHCl- structures (i.e., 2,3,4,5-C10Cl4 and 2,3,4,5,6,7,8,9-C10Cl8)
had lower A descriptor values compared to CPs with the same number but a more distributed
chlorination pattern (i.e., 4,5,7,8-C11Cl4, 2,5,6,9-C10Cl4 and 1,2,5,6,9,10-C10Cl6). The differences in
ΔRI between constitutional isomers observed in the previous section are thus more related to
H-bond donating properties (A) of the isomers.
The polar property of chlorinated carbon moieties stems from the high electronegativity
of the Cl atom compared to that of the C atom. In a -CHCl- structure, the relatively high electron
affinity of Cl has an inductive effect on C which results in a positive partial charge on the H
atom. This makes the -CHCl- structure polar (positive S) and the H atom is then prone to act as a
H-bond donor (positive A). Such an inductive effect of Cl and the resulting H-bond donor
property are well known for small chloroalkanes such as dichloromethane (A = 0.1) and
chloroform (A = 0.15). However, in CP structures with vicinal -CHCl-, the Cl atom is often in
proximity of the H atom of the neighboring -CHCl- structure which appear to diminish the ability
of the H to fully act as a H-bond donor. Having 4 or more consecutive -CHCl- structures put each
H atom in an even more crowded environment and brings back A to near 0 (Fig. 3). This
interpretation is consistent with the existing knowledge on A for hexachlorocyclohexane (HCH)
isomers. A values for α- and γ-HCHs are 0, whereas β-HCH poses a significant A value (0.12).27
Because of the different rotational configurations of the six -CHCl- units, β-HCH can take a
conformation that maximizes the exposition of H atoms to the surrounding, whereas α- and γ-
HCHs cannot do so.
A CCl3-CH2-CHCl- structure in 1,1,1,3-C10Cl4 has a minimal H-bonding property (see Fig.
3), which may be only attributable to the single -CHCl-. The -CCl3 group has no H-bond donor
site and does not appear to make the neighboring -CH2- acidic (similar case for 1,1,1-
trichloroethane with A = 0). However, a single Cl on the terminal carbon in a CH2Cl-CHCl-
structure adds to H-bond donating properties of the CP (see A of 1,1,1,3-C10Cl4 < 1,1,1,3,9,10-
C10Cl6). 1,2,3,4,5,6-Cl10Cl6 also contains this substructure although A is low, possibly due to steric
effects or interference from the neighboring consecutive CHCl structure.
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The inconsistent results for SolGel-WAX and DB-225ms can have several causes. For
example, n-alkanes might undergo interfacial adsorption and can be retained under a mixed-
mode retention mechanism on polar columns, which makes n-alkanes less suitable as reference
compounds for determining RI values.28 The exact reason is however difficult to conclude from
the current data.
Figure 3. Solute descriptors E, A, S and L for a selection of CPs. S and A descriptors were
determined using RI values from all columns while omitting either the SolGel-WAX or the DB-
225ms column. Doing so has no influence on the determined E and L descriptor values.
COSMOthermX predictions
The COSMOthermX-predicted RIs correlated well with the measured RIs of CPs with an
R2 between 0.975 and 0.995 (Supplementary Fig. S4). There is even high 1:1 agreement
between predicted and measured RIs for SPB-Octyl, HP-5ms, and SolGel-WAX (RMSE: 44-72).
The agreement, however, was lower for the columns DB-17ms, InertCap-17ms and DB-225ms
(RMSE: 222-280). The CP group shows a trend that is not parallel to n-alkanes for these three
columns (Supplementary Fig. S4), and thus the discrepancy increases with increasing RI value.
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The polymer coating of these columns contains a high proportion of phenyl groups (50% phenyl
or diphenyl groups) and, apparently, the interaction properties of these groups with the CP
structures is not fully captured by COSMOthermX. To make use of the high correlations between
predicted and measured RIs, we applied an empirical correction to the predicted RI values by
using the regression formula of predicted vs measured RI values for CPs (Supplementary Fig.
S5). The results are shown in Fig. 4 and Supplementary Fig. S5. The RSME values after correction
were between 21 and 75.
ΔRI values were calculated using the predicted RIs to test whether COSMOthermX can
capture differences in polarity between CP congeners (Fig. 2C). Comparing Fig. 2B and 2C
indicates that the overall trend agrees well with the experimentally observed ΔRIs. Thus,
COSMOthermX correctly reflects polarity differences between CPs with differing chlorination
patterns. The only discrepancy appears that COSMOthermX slightly overestimates the ΔRI
values of CPs with many consecutive -CHCl- groups (i.e., 1,2,3,4,5,6-C11Cl6 and 2,3,4,5,6,7,8,9-
C10Cl8). This statement however is conditional, because these two congeners have many possible
diastereomers (16 and 70, respectively), for which COSMOthermX calculated a relatively wide
range of ΔRIs. Currently, we do not know which diastereomers are present in the analytical
standards.
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0
1000
2000
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4000
Measured RI
Pre
dic
ted
RI
HP-5msDB-17msInertCap-17msDB-225ms
SPB-Octyl
SolGel-WAX
Figure 4. The RI values for CP congeners predicted by COSMOthermX for all columns in this
study against the measured RI values from the GC system. Empirical corrections were applied to
RI predictions (see text).
Effects of diastereomerism
The range of predicted RI values by COSMOthermX shown in Supplementary Fig. S4 and
S5 indicates the potential effects of diastereomerism of the CP on the partition properties (e.g.,
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2,3,4,5,6,7,8,9-C10Cl8). COSMOthermX predicts an increasing range of RI with increasing polarity
of the polymer phase, which was also observed in the retention measurements on the GC
systems. While CPs with many possible diastereomers usually showed a wide range in measured
RI values, predicted RI values often span over an even wider range, suggesting that not all
possible diastereomers are present in the CP standards. Comparing the two diastereomers of
2,3,4,5,6,7,8,9-C10Cl8, with the highest and lowest predicted RI values on the DB-225ms column
((2R,3S,4S,5S,6S,7S,8S,9R)-2,3,4,5,6,7,8,9-C10Cl8 and (2R,3R,4S,5S,6S,7S,8R,9R)-2,3,4,5,6,7,8,9-
C10Cl8, predicted RI of 2721 and 2304, respectively), we can see that a difference in rotational
configurations around the chiral carbons can result in distinctly different three-dimensional
shapes (Fig. 5). Overall, according to the results from COSMOthermX, the difference between
diastereomers can greatly affect the 3D-structure of the CP molecules, which, in turn, affects
the interaction properties of the molecule and its partition behavior.
Figure 5. The lowest-energy conformers (_c0 suffix) of (2R,3S,4S,5S,6S,7S,8S,9R)-2,3,4,5,6,7,8,9-
C10Cl8 (A) and (2R,3R,4S,5S,6S,7S,8R,9R)-2,3,4,5,6,7,8,9-C10Cl8 (B), generated by COSMOconfX.
Both are diastereomers of 2,3,4,5,6,7,8,9-C10Cl8.
ConclusionsInspection of RI values of CPs from GC columns with different polarity shows that the
chlorination pattern plays an important role in determining polar interactions of CPs. Isolated
-CHCl- groups or a pair of two vicinal -CHCl- are more polar than patterns with three or more
consecutive -CHCl- groups. Polarity is also increased when a single Cl atom is present at the
terminal carbon (e.g., -CH2Cl), whereas three Cl atoms at the terminal (-CCl3) add least to
polarity of the CP molecules.
Determining ppLFER descriptors for CPs shows that polarity differs significantly between
CP chlorination patterns and confirm the importance of Cl positioning to the H-bond donating
properties (A) of CPs. The calculated solute descriptors show that H-bond interactions are lower
for CPs with many consecutive -CHCl- groups than for CPs with a more distributed chlorination
pattern.
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Predictions from COSMOthermX show that the quantum chemically based modelling
approach is capable of predicting RI values and can reflect the effect of variations in chlorination
pattern on the interaction properties of CPs. This result supports the general accuracy of
COSMOthermX to predict partition coefficients of CPs. As future work, retention time
predictions by COSMOthermX for a diverse set of congeners could be compared to measured
chromatograms of CPs in environmental samples or in complex technical mixtures to infer the
congener compositions present.
Data availabilityThe authors declare that all data supporting the findings of this study are available
within the article and its supplementary information file.
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Author informationCorresponding author
Jort Hammer
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ORCID: 0000-0002-1403-2631
Additional informationThe authors declare no competing financial interest.
Supplementary information is available for this paper at...
Author contributionsStudy design: JH, SE. GC-MS measurements: JH, HM. COSMO-RS calculations: JH. Data
evaluation: JH, SE. Drafting of manuscript: JH. Revising of manuscript: JH, SE, HM.
AcknowledgementsThis research was supported by the Environment Research and Technology Development
Fund SII-3-1 (JPMEERF18S20300) of the Environmental Restoration and Conservation Agency,
Japan. COSMOconfX and TURBOMOL calculations were performed with the NIES supercomputer
system. We thank Kai-Uwe Goss for their valuable comments on the manuscript, and Yoshinori
Fujimine (Otsuka Pharmaceutical Co., Ltd.) for donating the standard solution of 1,5,5,6,6,10-
C10Cl6.
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download fileview on ChemRxiv20200803-CPs_GC-COSMO_Hammer-Endo.docx (919.36 KiB)
Congener-specific partition properties of chlorinated paraffins 1
evaluated with COSMOtherm and gas chromatographic retention 2
indices 3
4
Jort Hammer*, Hidenori Matsukami, Satoshi Endo 5
6
National Institute for Environmental Studies (NIES), Center for Health and Environmental Risk 7
Research, Onogawa 16-2, 305-8506 Tsukuba, Ibaraki, Japan 8
9
*Corresponding author 10
Abstract 11
Chlorinated Paraffins (CPs) are high volume production chemicals and have been found 12
in various organisms including humans and in environmental samples from remote regions. It is 13
thus of great importance to understand the physical-chemical properties of CPs. In this study, gas 14
chromatographic (GC) retention indexes (RIs) of 26 CP congeners were measured on various polar 15
and nonpolar columns to investigate the relationships between the molecular structure and the 16
partition properties. Retention measurements show that analytical standards of individual CPs 17
often contain several stereoisomers. RI values show that chlorination pattern have a large 18
influence on the polarity of CPs. Single Cl substitutions (-CHCl-, -CH2Cl) generally increase polarity 19
of CPs. However, many consecutive -CHCl- units (e.g., 1,2,3,4,5,6-C11Cl6) increase polarity less 20
than expected from the total number of -CHCl- units. Polyparameter linear free energy 21
relationship descriptors show that polarity difference between CP congeners can be explained 22
by the H-bond donating properties of CPs. RI values of CP congeners were predicted using the 23
quantum chemically based prediction tool COSMOthermX. Predicted RI values correlate well with 24
the experimental data (R2, 0.975–0.995), indicating that COSMOthermX can be used to accurately 25
predict the retention of CP congeners on GC columns. 26
27
Introduction 28
Chlorinated Paraffins (CPs) are a group of substances that are applied in various products 29
as plasticizers, coolants and flame retardants because of their chemical and thermal stability.1 30
CPs are high-volume production chemicals (>1 million metric tonnes yr-1) and are regularly 31
released into the environment during production, transportation, and recycling processes and 32
through leaching and volatilization from landfills.2–4 Short-chain chlorinated paraffins (SCCPs; C10-33
C13) are found to be persistent, bioaccumulative and toxic (PBT) to aquatic organisms. In 2017, 34
SCCPs were classified as persistent organic pollutants (POPs) under the Stockholm Convention 35
and subsequently the production of SCCPs has stopped in the US, Japan, Canada and Europe, and 36
will soon be restricted in China.5,6 Since the PBT properties of medium-chain (MCCPs: C14-C17) and 37
long-chain (LCCPs; C18 and longer) chlorinated paraffins are less studied and a matter of debate, 38
they are currently still being produced and used as alternatives for SCCPs.7 Therefore, the overall 39
world-wide production of CPs still upholds its increasing trend from the 1950s, albeit with a 40
recent shift from SCCPs towards MCCPs and LCCPs. 41
CP molecules are usually produced by free-radical chlorination of n-alkanes. This 42
chlorination reaction shows low positional selectivity and produces many congeners and isomers 43
and does not discriminate between stereoisomers.8 CP mixtures can therefore comprise 44
thousands of congeners with differing chain lengths and chlorination patterns. Currently, due to 45
the complexity of CP mixtures and the lack of analytical standards, no analytical methods are 46
available for the identification of individual congeners in CP mixtures or any samples 47
contaminated with CPs.9 The large variability in molecular structure suggests that intermolecular 48
interaction properties also vary substantially. Intermolecular interactions determine the 49
partitioning behavior of CPs and need to be understood to describe the environmental fate, 50
bioaccumulation, and toxicity of CPs. The broad bands of CP signals observed in chromatographic 51
analysis do suggest that congeners have a range of partition properties.10 52
The objective of this work is to describe the relationship between structure and molecular 53
interaction properties of CPs through experimental and quantum chemically based approaches. 54
Gas chromatography (GC) was used to experimentally investigate the molecular interaction 55
properties, as the retention time of the analyte on a GC column is directly related to the 56
molecular interactions between the column coating and the analyte molecule. Different GC 57
column coatings were selected with a range of polarity to elucidate the polar interaction 58
properties of CPs. The physico-chemical properties of CP congeners were evaluated by deriving 59
poly-parameter linear free energy relationship (ppLFER) descriptors from the measured data. 60
Lastly, retention times were predicted using a quantum chemically based tool, COSMOthermX 61
(COSMOlogic GmbH & Co. KG). COSMOthermX has previously been used to predict partition 62
coefficients such as octanol-water partition coefficients for CPs.11,12 Because COSMOthermX 63
requires only the molecular structure as input parameter, it could be a useful tool to predict the 64
retention and, more generally, partition properties of CP congeners with diverse structures. 65
66
Methods 67
Chemicals 68
Analytical standards of 2,5,6,9-C10Cl4, 1,2,5,6,9,10-C10Cl6 and 2,3,4,5,6,7,8,9-C10Cl8 were 69
provided by Dr. Ehrenstorfer GmbH (Augsburg, Germany). Standards of 1,1,1,3-C10Cl4, 1,1,1,3-70
C11Cl4, 1,1,1,3-C12Cl4, 1,1,1,3-C13Cl4, 1,1,1,3-C14Cl4, 1,1,1,3,9,10-C10Cl6, 1,1,1,3,10,11-C11Cl6, 71
1,1,1,3,11,12-C12Cl6, 1,1,1,3,12,13-C13Cl6, 1,1,1,3,8,10,10,10-C10Cl8, 1,1,1,3,9,11,11,11-C11Cl8, 72
1,1,1,3,10,12,12,12-C12Cl8, 1,1,1,3,11,13,13,13-C13Cl8, 1,1,1,3,12,14,14,14-C14Cl8, 1,2,9,10-73
C10Cl4, 1,2,10,11-C11Cl4, 1,2,13,14-C14Cl4, 1,2,3,4,5,6-C11Cl6, 4,5,7,8-C11Cl4, 2,3,4,5-C10Cl4 and 74
2,3,4,5-C12Cl4 were obtained from Chiron AS (Trondheim, Norway). 1,5,5,6,6,10-C10Cl6, which 75
was commercially available from Cambridge Isotope Laboratories Inc. (Tewksbury, MA, USA), 76
was donated by Otsuka Pharmaceutical Co., Ltd. (Tokyo, Japan). C16, C18, C20-n-alcohols, a 77
mixture of C7-40-n-alkanes and a mixture of C4, C6, C8, C10, C12, C14, C16, C18, C20, C22, C24-methyl 78
esters (FAMEs) were obtained from Sigma-Aldrich Japan (Tokyo, Japan). C8, C10, C12-n-alcohols 79
were obtained from Tokyo Chemical Industry (Tokyo, Japan). A mixture of polycyclic aromatic 80
hydrocarbons (PAHs) containing naphthalene, acenaphthylene, acenaphthene, fluorene, 81
phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, 82
benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, 83
indeno[1,2,3-cd]pyrene and benzo[ghi]perylene was obtained from Sigma-Aldrich Japan (Tokyo, 84
Japan). Specifics on purities and concentrations of the CP analytical standards can be found in 85
Supplementary Table S1. 86
87
Columns 88
Six GC columns were used for the retention measurements in this study (Table 1). The GC 89
columns were selected to cover a wide range of polarity based on polarity scales provided by 90
manufacturers. The SPB-Octyl column is of nonpolar nature and the least polar column in this 91
study. Its coating consists of poly(50% n-octyl/50% methylsiloxane) and exerts retention mainly 92
via van der Waals interactions. The polar property of columns HP-5ms, InertCap-17ms and DB-93
17ms originates from the presence of phenyl groups in the dimethylsiloxane (HP-5ms and 94
InertCap-17ms) or silarylene-siloxane polymer (DB-17ms) structure of the column coating. These 95
columns contain 5% or 50% phenyl groups. Phenyl groups have π electrons that have weak 96
hydrogen (H)-bond accepting properties. The DB-225ms column, with a coating of 50% 97
cyanopropylphenyl/50% dimethylsiloxane-equivalent silarylene-siloxane copolymer, contains a 98
polar nitrile group that acts as a H-bond acceptor. The polar property of the SolGel-WAX column 99
originates from the ether oxygen atoms in poly(ethylene glycol), which has strong H-bond 100
accepting properties. All columns had the dimension of 30 m 0.25 mm 0.25 μm. 101
102
Retention measurements 103
A program with linear oven temperature increase was applied on all columns until the 104
recommended maximum temperature was reached (240-300°C). Helium was used as carrier gas 105
and a flow rate of 1.2 mL/min was maintained throughout all measurements. Retention 106
measurements for SPB-Octyl, DB-17ms, DB-225ms, and SolGel-WAX were performed using cool 107
on-column injections on an Agilent 7890 GC, followed by atmospheric pressure chemical 108
ionization (APCI) and mass selective detection (Agilent 6530 QTOF-MS) (See Supplementary 109
Section S2 for the optimization of APCI-QTOF-MS parameters for CPs). An injection volume of 2 110
μL was used. The on-column injector temperature was kept at the initial oven temperature (60 111
or 70°C) for 0.1 min and increased with 100°C/min to the maximum oven temperature. The oven 112
temperature was kept at 60 or 70°C for 0.1 min and increased with 10°C/min to the maximum 113
temperature shown in Table 1. More details are stated in the Supplementary Section S2. 114
Retention measurements of SPB-Octyl and SolGel-WAX were also performed on a different 115
system (7890A/7000A triple quadrupole GC/MS, Agilent Technologies) and HP-5ms and InertCap-116
17ms only on this system because of its better availability in our laboratory. On the triple 117
quadrupole GC/MS system, splitless injection at 250°C and electron ionization (EI) were used. 118
Peak patterns were similar on both systems, and the retention indices (RIs; see below for the 119
definition) differed only by 7 on average and 20 in the worst case. In contrast to the EI-MS 120
detector, the APCI-QTOF-MS method allows for a detection of pseudo-molecular ions and thus 121
better identification of peaks that belong to the stated CP isomers. Therefore, if the 122
measurements were done on both systems, data from APCI-QTOF-MS were considered for the 123
latter discussions. Peak identifications for the EI-MS chromatograms of HP-5ms and InertCap-124
17ms were performed by using the APCI-TOF-MS chromatograms of SPB-Octyl and DB-17ms, 125
respectively, as reference, because the peak patterns were highly similar (see the results section). 126
127
Table 1. Polymer coating compositions of the GC columns and structures of the surrogate 128
molecules used in COSMOthermX. The circled parts (red) on the molecular fragments refer to the 129
groups that were disregarded using the weight string function in COSMOthermX. 130
GC system
Column Coating composition
according to
manufacturer
Manufacturer GC oven
temperature
program
GC system /
Detection
Fragments representing the polymer phase in
COSMOthermX
SPB-Octyl poly(50% n-octy/
50% dimethylsiloxane) Supelco
70 °C (1 min)
10 °C/min
280 °C (10 min)
Agilent 7890 GC /
Agilent 6530
QTOF-MS
HP-5ms poly(5% diphenyl/
95% dimethylsiloxane)
Agilent
Technologies
70 °C (0.1 min)
10 °C/min
280 °C (10 min)
Agilent 7890A GC/
Agilent 7000A
Triple Quad GC/MS
DB-17ms poly(50% phenyl/
50% dimethylsiloxane)1
Agilent
Technologies
60 °C (1 min)
10 °C/min
300 °C (10 min)
Agilent 7890 GC /
Agilent 6530
QTOF-MS
InertCap-17ms poly(50% diphenyl/
50% dimethylsiloxane) GL Sciences
70 °C (1 min)
20 °C/min
300 °C (10 min)
Agilent 7890A GC /
Agilent 7000A
Triple Quad GC/MS
DB-225ms
poly(50% cyano-
propylphenyl/ 50%
dimethylsiloxane) 1
Agilent
Technologies
70 °C (0.1 min)
10 °C/min
240 °C (15 min)
Agilent 7890 GC /
Agilent 6530
QTOF-MS
SolGel-WAX Polyethylene glycol SGE Analytical
Science
70 °C (1 min)
10 °C/min
280 °C (5 min)
Agilent 7890 GC /
Agilent 6530
QTOF-MS
1 Silarylene-siloxane copolymer; 2 Instead of 5 and 95% mole fractions, 5.3 and 94.7% was used as the liquid phase composition 131 for HP-5ms in COSMOthermX since the larger fragment contains not only diphenylsiloxane, but dimethylsiloxane as well. 132
133
RIs of CPs, n-alcohols, n-alkylmethyl esters, PAHs and n-alkanes were obtained using the 134
linear temperature-programmed retention index system (LTPRI). This system is used to establish 135
retention indices for retention times measured under a program with linear temperature 136
increase:13,14 137
138
1) 139
140
where Rti is the retention time of the analyte, Rtx is the retention time of the n-alkane eluting 141
directly before Rti, Rtx+1 is the retention time of the n-alkane eluting directly after Rti and RIx is 142
the retention index of the n-alkane that corresponds to Rtx. The retention indices of n-alkanes 143
are defined as its number of carbon atoms times a hundred. 144
145
ppLFER descriptors 146
ppLFERs are useful in characterizing interaction properties that determine partitioning 147
behavior of chemicals. ppLFERs are multiple linear regression models that use several solute 148
descriptors as independent variables for the calculation of partition coefficients.15 The most 149
frequently used ppLFER for the gas-condensed phase partitioning, established by Abraham et 150
al,16 has the general form: 151
152
log K = c + eE + sS + aA + bB + lL 2) 153
154
where log K is the logarithmic partition coefficient. The uppercase letters on the right-hand side 155
of the equation are the solute descriptors: E, excess molar refraction; S, dipolarity/polarizability 156
parameter; A, H-bond donating property; B, H-bond accepting property and L, logarithmic 157
hexadecane-air partition coefficient. The lowercase letters are the system parameters. Each term 158
quantitatively describes the energetic contribution of a molecular interaction to log K. Since none 159
of the columns from the current study has H-bond donating properties, the bB term can be 160
ignored. Solute descriptors S and A are both responsible for the polar interactions of the 161
chemical: S is related to the surface electrostatic property and is thought to represent polar 162
interactions that result in part from the partial charge distribution over the molecular surface.17 163
A reflects more specific interactions resulting from H-bond donating sites of the solute molecule. 164
The L solute descriptor describes the non-specific van der Waals interactions and also includes 165
the energy needed for cavity formation.15,18 The eE term also describes the van der Waals 166
interactions but usually has only minor contributions to log K. For more detailed explanations of 167
the equation, we refer to refs 13-15. 168
𝑅𝐼 =𝑅𝑡𝑖 − 𝑅𝑡𝑥𝑅𝑡𝑥+1 − 𝑅𝑡𝑥
× 100 + 𝑅𝐼𝑥
In this study, temperature-programmed RIs instead of log K are correlated with the 169
ppLFER descriptors. Because temperature-programmed RI is related but not directly proportional 170
to log K,19 the use of ppLFER for the RI is an approximation. For a more accurate investigation, 171
isothermal retention measurements would be better suited, although much more time-172
consuming than temperature-programmed measurements, as isothermal measurements must 173
be performed at many temperatures to cover diverse CP structures. The purpose of using 174
ppLFERs in the current work is to compare semi-quantitatively the polar interaction properties of 175
CP congeners with varying structures and not to derive accurate solute descriptors that could be 176
used for later predictions. 177
178
Prediction of RI with COSMOthermX 179
COSMOthermX software is based on the COSMO-RS theory, which uses quantum 180
mechanics and statistical thermodynamics calculations to determine the chemical potential of a 181
solute in solution and can thereby predict partition coefficients. Gas-GC coating (i.e., air-polymer) 182
partition coefficients were predicted following the method by Goss (2011).20 Molecular 183
structures of CPs, reference compounds and polymer coatings were expressed with SMILES 184
strings, which were then converted to SDF files. Quantum chemical calculations and conformer 185
selection were performed using COSMOconfX (version 4.3, COSMOlogic) with TURBOMOL 7.3, 186
which yield a complete set of relevant conformations with full geometry optimization in the gas 187
phase and in the conductor reference state. The gas phase energy and COSMO files of the CPs 188
and reference compounds were then used in the COSMOthermX software (version 19.04; 189
parameterization: BP_TZVPD_FINE_19) to calculate air-polymer partition coefficients (Kair-polymer). 190
To represent the molecular structure of polymer coating, monomers or oligomers of the coating 191
polymer structure provided by the manufacturer were used. For the quantum chemical 192
calculations performed by COSMOconfX, the end groups of these monomer or oligomer were 193
end-capped with CH3 groups. The CH3 groups were later disregarded during COSMOthermX 194
calculations by giving a weighting factor of 0, following the approach by Goss (2011).20 All these 195
surrogate structures used for coating polymers are shown in Table 1. The polymer structure of 196
the HP-5ms column consists of 5% diphenylsiloxane and 95% dimethylsiloxane and we 197
represented this structure with a mixture of diphenylsiloxane and dimethylsiloxane in the 198
respective mole fractions (see Table 1) in the COSMOthermX calculations. For the SolGel-WAX 199
column, an end-capped trimer of ethylene glycol was used, as in ref 17. 200
All calculations in COSMOthermX were performed with the combinatorial term switched 201
off, as is recommended for polymer by the COSMOthermX user guide.22,23 All conformers 202
generated by COSMOconfX of the target chemicals were used for the calculation of air-polymer 203
partition coefficients. However, to reduce calculation times, only the top 5 low-energy 204
conformers returned by COSMOconfX (_c0 to _c4 suffixes) were selected to represent the 205
polymer phases. For some CPs, COSMOconfX returned conformers with R or S configurations that 206
were inconsistent with the input structure. This problem did not occur when we turned off RDKit 207
and only used Balloon for the generation initial conformers on the Windows version of 208
COSMOconfX. 209
For each chemical and coating phase, Kair-polymer was predicted at 5 temperature steps 210
between 373.15 and 573.15 K. Then, linear regression between log Kair-polymer and 1/T was 211
established, and a hypothetical eluting temperature was interpolated at a column-specific, 212
characteristic Kair-polymer value that is derived from experimental data. This eluting temperature 213
was considered analogous to the retention time and used to derive RI, following eq 2. A more 214
detailed explanation about how RI values were predicted from COSMOthermX calculations is 215
presented in the Supplementary Section S1. 216
Because the stereometric structure of the isomers present in the CP standards is unknown, 217
partition coefficients were calculated for all possible diastereomers using COSMOthermX. A pair 218
of enantiomers was represented by a single structure in the COSMOthermX calculation, because 219
partition coefficients of enantiomers are the same in isotropic phases. The predictability of the 220
COSMOthermX program was tested by comparing the mean of predicted RIs for all possible 221
diastereomers and the weighted mean of the measured RI values of the CP standards from the 222
GC system. RI values of PAHs were calculated but not used in testing the predictability of 223
COSMOthermX, as their predicted RI values were systematically deviated from the measured 224
values (see Supplementary Table S4). 225
226
227
Results and discussion 228
Determination of GC retention times and RI 229
Retention measurements showed the presence of multiple peaks in most of the CP 230
analytical standards. Generally, CP congeners with a high number of possible diastereomers given 231
their molecular structure showed multiple peaks with a substantial peak area of the same 232
(pseudo)molecular ion. For example, on the SPB-Octyl column, 10 peaks within a minute of 233
retention time were found for 1,2,3,4,5,6-C11Cl6, which has 10 possible diastereomers (a pair of 234
enantiomers are considered one structure). In contrast, 1,1,1,3,9,10-C10Cl6 (2 possible 235
diastereomers) only showed one peak (Supplementary Fig. S1A and S1B). For one standard, 236
2,5,6,9-C10Cl4 (6 possible diastereomers), the manufacturer-provided certificate of analysis 237
stated the presence of three diastereomers without details on the exact stereometric structure 238
(e.g., S and R notation). While we indeed observed three peaks on the nonpolar SPB-Octyl column, 239
7 peaks were found on the most polar SolGel-WAX column (Fig. 1), showing increased separation 240
through polar interactions. As exceptional cases, 1,2,5,6,9,10-C10Cl6 (6 possible diastereomers) 241
only showed one peak on all columns (Supplementary Fig. S1C) and 2,3,4,5,6,7,8,9-C10Cl8 (72 242
possible diastereomers) showed 3 peaks on the SPB-Octyl column, and only 1 peak on the SolGel-243
WAX (Supplementary Fig. S1D). These standards likely contain a limited number of diastereomers. 244
Some CP standards with only few or no possible diastereomers resulted in a higher number of 245
peaks. For example, 1,1,1,3-C10Cl4 (no diastereomer) showed 5 peaks over 3 minutes of retention 246
time on the SPB-Octyl column (Supplementary Fig. S1E) and 4 peaks over 5 minutes of retention 247
time on the SolGel-WAX column. Most of the peaks in these chromatograms were small and are 248
likely constitutional isomers (i.e., impurities). 249
250
251 Figure 1. The Chromatogram of 2,3,6,9-C10Cl4 measured on the SolGel-WAX column. The 252
manufacturer-provided certificate of analysis of this analytical standard stated the presence of 253
three diastereomers. 254
255
As a representative RI value for a CP congener with multiple peaks, the mean of the RI 256
values weighted by the peak areas was calculated and used in the following discussions. While 257
we are aware that peak areas do not always reflect the relative abundance of CP isomers 258
present,24 this approach deemed better than simply calculating the mean of RIs for all peaks 259
without weighting, particularly in cases where one or a few major peaks appear with many small 260
peaks. 261
We note that no retention times of 1,1,1,3,11,12-C12Cl6, 1,1,1,3,9,10,10,10-C10Cl8 and 262
1,5,5,6,6,10-C10Cl6 could be determined on the SolGel-WAX column, as their peaks were broad 263
and the response was low (Supplementary Fig. S1F). This peak broadening is probably because of 264
thermal degradation, as a high temperature (280°C) was needed to elute these congeners. 265
Indeed, 1,5,5,6,6,10-C10Cl6 and 1,1,1,3,9,10,10,10-C10Cl8 were detected on the other highly polar 266
column DB-225ms, for which a lower temperature (240°C) for elution was applied. 267
268
Comparison of RIs on polar and nonpolar columns 269
Since polar compounds are retained more by polar coatings, comparing RI values between 270
columns of different polarity allows for the characterization of the polar interaction properties 271
of CP molecules and substructures. RIs of CPs on polar columns were always higher than those 272
on the nonpolar SPB-Octyl column, showing the significance of polar interaction properties for 273
all CP standards (Fig. 2). The range of RIs (or separation of diastereomer/constitutional isomer 274
peaks) for each CP standard was usually greater on polar columns, meaning that the isomers are 275
better separated with polar retention mechanisms instead of van der Waals interactions only. 276
A series of CP congeners with -CH2- increments show that RI on all columns increased with 277
102 to 119 per addition of -CH2- to the alkyl chain. These values are similar to the RI values of n-278
alcohols (102–107 per methylene) and n-alkylmethyl esters (100–105 per methylene, see 279
Supplementary Fig. S2). 280
Chlorine substitution on the alkyl chain generally increased RI to an extent depending on 281
the column polarity and the position of Cl. For example, the RI of 1,2,9,10-C10Cl4 on the SPB-Octyl 282
column is greater by 229 than that of a constitutional isomer 1,1,1,3-C10Cl4. The retention on the 283
SPB-Octyl column is driven by van der Waals interactions, which are correlated to the molecular 284
surface area of the molecule.25 The four Cl atoms of 1,2,9,10-C10Cl4 are distributed over the alkyl 285
chain and increase the molecular surface area more than the four Cl atoms of 1,1,1,3-C10Cl4 that 286
are shifted on one side. 287
Figure 2B shows ΔRI, defined as the RI of a column subtracted by the RI of SPB-Octyl to 288
clarify the contributions of polar interactions to the retention. Larger ΔRI values are observed 289
with increasing column polarity, while the trends of ΔRI over different congeners are similar for 290
all columns. Generally, a single Cl substitution on -CH2- to -CHCl- increases the polarity of CPs. 291
However, actual contributions appear to depend strongly on the neighboring structure of the -292
CHCl- group. A vicinal substitution pattern (-CHCl-CHCl-) does not increase the polarity so much 293
as an isolated -CHCl-. This is clearly shown with 2,3,4,5,6,7,8,9-C10Cl8, which shows only an 294
intermediate ΔRI although having the highest number of -CHCl- units. In a vicinal substitution 295
pattern, the proximity of -CHCl- groups might interfere with, and lower, the polarity and/or H-296
bond properties of a neighboring -CHCl- group. In contrast, a single Cl substitution on a terminal 297
carbon (-CH3) is less influenced by Cl on the neighboring carbon. Comparison of the 5 tetrachloro 298
(Cl4) congeners is illustrative for these trends: 2,5,6,9-C10Cl4 (2 isolated Cl and a pair of vicinal Cl) 299
and 1,2,9,10-C10Cl4 (2 pairs of vicinal Cl at the ends) show the highest ΔRI, followed by 4,5,7,8- 300
C11Cl4 (2 pairs of vicinal Cl) and 2,3,4,5-C10Cl4 (4 consecutive, vicinal Cl). 1,1,1,3-C10Cl4 is the least 301
polar of the measured CPs even though it contains one isolated -CHCl- group. This shows that 302
CCl3 has a much smaller contribution to polarity than 3 -CHCl-. It is interesting to note that ΔRI 303
of 1,1,1,3-C10Cl4 is about half that of 1,1,1,3,9,10,10,10-C10Cl8. As the latter has double the CCl3-304
CH2-CHCl- substitution pattern, this observation suggests that the additivity principle may hold 305
for the polarity of CPs, provided that the two structural units are far enough apart. The highest 306
ΔRI was observed for 1,2,5,6,9,10-C10Cl6 (3 pairs of vicinal Cl, of which 2 pairs at the ends). 307
1,5,5,6,6,10-C10Cl6 is the only CP standard with double chlorinated carbons and shows the second 308
highest ΔRI. Comparison to 1,2,5,6,9,10-C10Cl6 suggests that -CCl2-CCl2- may be less polar than 4 309
chlorines all as vicinal -CHCl- groups. Overall, the total number of -CHCl- groups is not decisive for 310
the polarity of CPs and the chlorination pattern needs to be considered. 311
312
313 Figure 2. The measured RI on GC columns (A), the measured RIs subtracted by the measured RI 314
on the SPB-Octyl column (ΔRI) (B), and RI values predicted by COSMOthermX subtracted by 315
predicted RI values of the SPB-Octyl column (C) for a selection of CP standards. The compounds 316
are ordered according to the ΔRI for DB-225ms (polar column with data available for most CPs). 317
The vertical error bars in panels A and B show the range of measured RIs for multiple peaks, 318
while the vertical error bars in panel C show the range of predicted RI values for CPs with 319
multiple diastereomers. Corrections were applied to predicted RIs (see text). 320
321
Describing polarity using ppLFERs 322
To investigate the types and the extent of polar interactions with CPs, ppLFER solute 323
descriptors were derived. The A and S descriptors describe the polarity of the CPs relevant for GC 324
retention times. First, the E values of CPs were obtained using the structure based estimation 325
method from the UFZ-LSER database,26 because E has been considered a simple additive 326
property.16 The E values obtained are presented in Supplementary Table S3a. Second, L values 327
were determined from SPB-Octyl data. The SPB-Octyl column exerts minimal polar interactions, 328
and system parameters s and a were therefore set to 0. Thus, 329
330
RI = c + eE + lL 3) 331
332
Here, the measured RI values and the solute descriptors (E, L) of n-alcohols, n-alkylmethyl esters, 333
n-alkanes and PAHs (Table 2b) were used to calibrate system parameters (c, e, l) for SPB-Octyl by 334
least-square multiple linear regression. The result is given in Supplementary Table S2. The solute 335
descriptors for these chemicals were obtained from the UFZ-LSER database.26 Then, from the 336
system parameters and E and RI values of CPs, L values were calculated (Supplementary Table 337
S3a): 338
339
L = (RI – c – eE)/l 4) 340
341
The A and S solute descriptors of CPs were calculated from the rest of the data. The 342
ppLFER model fit the calibration data well with R2 of 0.995-0.997 and the standard deviation (SD) 343
of 36-59. System parameters for all columns were qualitatively in good agreement with those 344
reported by Poole et al. using isothermal measurements (Supplementary Table S2). The a and s 345
system parameters are in the order of the expected polarity of the columns: SPB-Octyl < HP-5ms 346
<< DB-17ms < InertCap-17ms << DB-225ms < SolGel-WAX. The ppLFER equations for the columns 347
were transformed into: 348
349
RI – c – eE – lL = sS + aA 5) 350
351
S and A were determined from multiple linear regression with 0 intercept. The results are given 352
in Supplementary Fig. S3. The standard errors of S and A were relatively high. This can be 353
because of the incompatible results for the two most polar columns, DB-225ms and SolGel-354
WAX. As the e, a and s system parameters of the SolGel-WAX column are higher than those of 355
the DB-225ms column, one would expect that RIs on the SolGel-WAX column would also be 356
higher for all CPs. However, as Fig. 2 shows, RIs for SolGel-WAX were just as much as or even 357
lower than those for DB-225ms. These conflicting results may cause a relatively large error in A 358
and S. 359
As an attempt, we obtained A and S with the RI data for all but the SolGel-WAX column 360
and for all but the DB-225ms column. While the resulting A and S descriptor values differ (on 361
average 0.40 and 0.16, respectively), the trend across CP congeners remains the same between 362
the two approaches (Fig. 3). The S descriptor generally increased with the number of chlorinated 363
carbons. The lowest values were found for 1,1,1,3-C10Cl4 and highest for 1,2,5,6,9,10-C10Cl6 and 364
2,3,4,5,6,7,8,9-C10Cl8 (Fig. 3 and Supplementary Table S2). The A solute descriptor values were 365
not related to the number of chlorines but rather to specific chlorination patterns. Substructures 366
-CH2Cl and -CHCl- tend to increase A, but with the striking exception that compounds with 367
consecutive -CHCl- structures (i.e., 2,3,4,5-C10Cl4 and 2,3,4,5,6,7,8,9-C10Cl8) had lower A 368
descriptor values compared to CPs with the same number but a more distributed chlorination 369
pattern (i.e., 4,5,7,8-C11Cl4, 2,5,6,9-C10Cl4 and 1,2,5,6,9,10-C10Cl6). The differences in ΔRI between 370
constitutional isomers observed in the previous section are thus more related to H-bond 371
donating properties (A) of the isomers. 372
The polar property of chlorinated carbon moieties stems from the high electronegativity 373
of the Cl atom compared to that of the C atom. In a -CHCl- structure, the relatively high electron 374
affinity of Cl has an inductive effect on C which results in a positive partial charge on the H atom. 375
This makes the -CHCl- structure polar (positive S) and the H atom is then prone to act as a H-bond 376
donor (positive A). Such an inductive effect of Cl and the resulting H-bond donor property are 377
well known for small chloroalkanes such as dichloromethane (A = 0.1) and chloroform (A = 0.15). 378
However, in CP structures with vicinal -CHCl-, the Cl atom is often in proximity of the H atom of 379
the neighboring -CHCl- structure which appear to diminish the ability of the H to fully act as a H-380
bond donor. Having 4 or more consecutive -CHCl- structures put each H atom in an even more 381
crowded environment and brings back A to near 0 (Fig. 3). This interpretation is consistent with 382
the existing knowledge on A for hexachlorocyclohexane (HCH) isomers. A values for α- and γ-383
HCHs are 0, whereas β-HCH poses a significant A value (0.12).27 Because of the different 384
rotational configurations of the six -CHCl- units, β-HCH can take a conformation that maximizes 385
the exposition of H atoms to the surrounding, whereas α- and γ-HCHs cannot do so. 386
A CCl3-CH2-CHCl- structure in 1,1,1,3-C10Cl4 has a minimal H-bonding property (see Fig. 3), 387
which may be only attributable to the single -CHCl-. The -CCl3 group has no H-bond donor site 388
and does not appear to make the neighboring -CH2- acidic (similar case for 1,1,1-trichloroethane 389
with A = 0). However, a single Cl on the terminal carbon in a CH2Cl-CHCl- structure adds to H-390
bond donating properties of the CP (see A of 1,1,1,3-C10Cl4 < 1,1,1,3,9,10-C10Cl6). 1,2,3,4,5,6-391
Cl10Cl6 also contains this substructure although A is low, possibly due to steric effects or 392
interference from the neighboring consecutive CHCl structure. 393
The inconsistent results for SolGel-WAX and DB-225ms can have several causes. For 394
example, n-alkanes might undergo interfacial adsorption and can be retained under a mixed-395
mode retention mechanism on polar columns, which makes n-alkanes less suitable as reference 396
compounds for determining RI values.28 The exact reason is however difficult to conclude from 397
the current data. 398
399
400 Figure 3. Solute descriptors E, A, S and L for a selection of CPs. S and A descriptors were 401
determined using RI values from all columns while omitting either the SolGel-WAX or the DB-402
225ms column. Doing so has no influence on the determined E and L descriptor values. 403
404
COSMOthermX predictions 405
The COSMOthermX-predicted RIs correlated well with the measured RIs of CPs with an R2 406
between 0.975 and 0.995 (Supplementary Fig. S4). There is even high 1:1 agreement between 407
predicted and measured RIs for SPB-Octyl, HP-5ms, and SolGel-WAX (RMSE: 44-72). The 408
agreement, however, was lower for the columns DB-17ms, InertCap-17ms and DB-225ms (RMSE: 409
222-280). The CP group shows a trend that is not parallel to n-alkanes for these three columns 410
(Supplementary Fig. S4), and thus the discrepancy increases with increasing RI value. The polymer 411
coating of these columns contains a high proportion of phenyl groups (50% phenyl or diphenyl 412
groups) and, apparently, the interaction properties of these groups with the CP structures is not 413
fully captured by COSMOthermX. To make use of the high correlations between predicted and 414
measured RIs, we applied an empirical correction to the predicted RI values by using the 415
regression formula of predicted vs measured RI values for CPs (Supplementary Fig. S5). The 416
results are shown in Fig. 4 and Supplementary Fig. S5. The RSME values after correction were 417
between 21 and 75. 418
ΔRI values were calculated using the predicted RIs to test whether COSMOthermX can 419
capture differences in polarity between CP congeners (Fig. 2C). Comparing Fig. 2B and 2C 420
indicates that the overall trend agrees well with the experimentally observed ΔRIs. Thus, 421
COSMOthermX correctly reflects polarity differences between CPs with differing chlorination 422
patterns. The only discrepancy appears that COSMOthermX slightly overestimates the ΔRI values 423
of CPs with many consecutive -CHCl- groups (i.e., 1,2,3,4,5,6-C11Cl6 and 2,3,4,5,6,7,8,9-C10Cl8). 424
This statement however is conditional, because these two congeners have many possible 425
diastereomers (16 and 70, respectively), for which COSMOthermX calculated a relatively wide 426
range of ΔRIs. Currently, we do not know which diastereomers are present in the analytical 427
standards. 428
429
430 Figure 4. The RI values for CP congeners predicted by COSMOthermX for all columns in this 431
study against the measured RI values from the GC system. Empirical corrections were applied to 432
RI predictions (see text). 433
434
Effects of diastereomerism 435
The range of predicted RI values by COSMOthermX shown in Supplementary Fig. S4 and 436
S5 indicates the potential effects of diastereomerism of the CP on the partition properties (e.g., 437
2,3,4,5,6,7,8,9-C10Cl8). COSMOthermX predicts an increasing range of RI with increasing polarity 438
of the polymer phase, which was also observed in the retention measurements on the GC 439
systems. While CPs with many possible diastereomers usually showed a wide range in measured 440
0
1000
2000
3000
4000
0
1000
2000
3000
4000
Measured RI
Pre
dic
ted
RI
HP-5msDB-17msInertCap-17msDB-225ms
SPB-Octyl
SolGel-WAX
RI values, predicted RI values often span over an even wider range, suggesting that not all 441
possible diastereomers are present in the CP standards. Comparing the two diastereomers of 442
2,3,4,5,6,7,8,9-C10Cl8, with the highest and lowest predicted RI values on the DB-225ms column 443
((2R,3S,4S,5S,6S,7S,8S,9R)-2,3,4,5,6,7,8,9-C10Cl8 and (2R,3R,4S,5S,6S,7S,8R,9R)-2,3,4,5,6,7,8,9-444
C10Cl8, predicted RI of 2721 and 2304, respectively), we can see that a difference in rotational 445
configurations around the chiral carbons can result in distinctly different three-dimensional 446
shapes (Fig. 5). Overall, according to the results from COSMOthermX, the difference between 447
diastereomers can greatly affect the 3D-structure of the CP molecules, which, in turn, affects the 448
interaction properties of the molecule and its partition behavior. 449
450
451 452
Figure 5. The lowest-energy conformers (_c0 suffix) of (2R,3S,4S,5S,6S,7S,8S,9R)-2,3,4,5,6,7,8,9-453
C10Cl8 (A) and (2R,3R,4S,5S,6S,7S,8R,9R)-2,3,4,5,6,7,8,9-C10Cl8 (B), generated by COSMOconfX. 454
Both are diastereomers of 2,3,4,5,6,7,8,9-C10Cl8. 455
456
Conclusions 457
Inspection of RI values of CPs from GC columns with different polarity shows that the 458
chlorination pattern plays an important role in determining polar interactions of CPs. Isolated -459
CHCl- groups or a pair of two vicinal -CHCl- are more polar than patterns with three or more 460
consecutive -CHCl- groups. Polarity is also increased when a single Cl atom is present at the 461
terminal carbon (e.g., -CH2Cl), whereas three Cl atoms at the terminal (-CCl3) add least to polarity 462
of the CP molecules. 463
Determining ppLFER descriptors for CPs shows that polarity differs significantly between 464
CP chlorination patterns and confirm the importance of Cl positioning to the H-bond donating 465
properties (A) of CPs. The calculated solute descriptors show that H-bond interactions are lower 466
for CPs with many consecutive -CHCl- groups than for CPs with a more distributed chlorination 467
pattern. 468
Predictions from COSMOthermX show that the quantum chemically based modelling 469
approach is capable of predicting RI values and can reflect the effect of variations in chlorination 470
pattern on the interaction properties of CPs. This result supports the general accuracy of 471
COSMOthermX to predict partition coefficients of CPs. As future work, retention time predictions 472
by COSMOthermX for a diverse set of congeners could be compared to measured chromatograms 473
of CPs in environmental samples or in complex technical mixtures to infer the congener 474
compositions present. 475
476
Data availability 477
The authors declare that all data supporting the findings of this study are available 478
within the article and its supplementary information file. 479
480
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545
Author information 546
Corresponding author 547
Jort Hammer 548
ORCID: 0000-0002-1403-2631 550
551
552
Additional information 553
The authors declare no competing financial interest. 554
Supplementary information is available for this paper at... 555
556
Author contributions 557
Study design: JH, SE. GC-MS measurements: JH, HM. COSMO-RS calculations: JH. Data 558
evaluation: JH, SE. Drafting of manuscript: JH. Revising of manuscript: JH, SE, HM. 559
560
Acknowledgements 561
This research was supported by the Environment Research and Technology Development 562
Fund SII-3-1 (JPMEERF18S20300) of the Environmental Restoration and Conservation Agency, 563
Japan. COSMOconfX and TURBOMOL calculations were performed with the NIES supercomputer 564
system. We thank Kai-Uwe Goss for their valuable comments on the manuscript, and Yoshinori 565
Fujimine (Otsuka Pharmaceutical Co., Ltd.) for donating the standard solution of 1,5,5,6,6,10-566
C10Cl6. 567
568
download fileview on ChemRxiv20200803-CPs_GC-COSMO_Hammer-Endo.pdf (1.27 MiB)
Congener-specific partition properties of chlorinated paraffins
evaluated with COSMOtherm and gas chromatographic retention
indices
Jort Hammer*, Hidenori Matsukami, Satoshi Endo
National Institute for Environmental Studies (NIES), Center for Health and Environmental Risk
Research, Onogawa 16-2, 305-8506 Tsukuba, Ibaraki, Japan
*Corresponding author
Supporting Information
Section S1: Prediction of RI using COSMOthermX
The surrogate molecules of the column coatings used consisted of a monomer or an oligomer from the
polymer structure (see Table 1 in the manuscript). For the quantum-mechanical calculations performed
by COSMOconfX, these surrogate molecules were end-capped with CH3 groups. Later, for the calculation
of partition coefficients, these groups were disregarded using the weight string function in COSMOthermX.
Since the combinatorial term in the free energy of partitioning is not well defined for polymers, all
calculations were performed with the combinatorial term turned off. To predict RI values of all compounds,
the calculated air-polymer partition coefficients (Kair/polymer) from COSMOthermX need to be converted to
RIs. While temperature-programmed RI is related but not directly proportional to Kair/polymer,1 we opted a
simple empirical approach for this conversion as described below.
As the GC measurements were performed under a program with linear temperature increase, the
retention time corresponds to the elution temperature of each compound. In COSMOthermX, a linear
relationship between log Kair/polymer and the reciprocal of temperature (1/T) was obtained for each
compound by calculating partition coefficients at 5 different temperatures (Fig. S6). Using this linear
relationship, the experimentally obtained elution temperatures for reference compounds (n-alkanes, n-
alcohols, n-alkylmethylesters) were converted to log Kair/polymer values (Fig. S6A). The resulting log Kair/polymer
values were specific to the column and were similar across the reference compounds (average SD = 0.15
in the current study). Note that compounds that eluted after the maximum temperature of the GC
program was reached were removed from consideration. The mean of these “elution” log Kair/polymer values
for reference compounds was calculated and was used to back-calculate the predicted elution
temperatures for all compounds including CPs (Figure S6B). Finally, RI values were computed from these
calculated elution temperatures using a modified version of equation 1 (i.e., where retention times were
replaced by elution temperatures). Note that log Kair/polymer of long alkanes (> C26) were extrapolated from
shorter alkanes because COMSOconfX calculation times were too long (> 5 days).
Section S2: GC-APCI-QTOF-MS parameter optimization
The APCI-QTOF-MS parameters were optimized for the identification of CP isomers, which were
detected by APCI in positive mode. Intense pseudo-molecular ions of the CP isomers were observed
corresponding to the dechlorinated and deprotonated molecules (Figs. S7a and S7b). Fragmentor
voltage, capillary voltage, corona current and gas temperature for enhancing ionization (Fig. 8) were
optimized and set to 150 V, 2500 V, 1.0 μA, and 350 °C, respectively.
Table S1. The analytical standards of CP isomers used in this study. (N.A., not available)
Supplier Cat No. Compound name Concentration
(μg/mL)
Purity
(%)
Dr Ehrenstorfer GmbH DRE-LA17356500CY 2,5,6,9-Tetrachlorodecane 10 98.3 Dr Ehrenstorfer GmbH DRE-LA14171500CY 1,2,5,6,9,10-Hexachlorodecane 10 99.9 Dr Ehrenstorfer GmbH DRE-ZA15705000CY 2,3,4,5,6,7,8,9-Octachlorodecane 1 99.9 Chiron AS 1662.10-100-IO 1,1,1,3-Tetrachlorodecane 100 99.9 Chiron AS 1649.11-100-IO 1,1,1,3-Tetrachloroundecane 100 97.3 Chiron AS 1651.12-100-IO 1,1,1,3-Tetrachlorododecane 100 94.5 Chiron AS 1653.13-100-IO 1,1,1,3-Tetrachlorotridecane 100 97.1 Chiron AS 1676.14-K-IO 1,1,1,3-Tetrachlorotetradecane 1000 N.A. Chiron AS 1622.10-100-IO 1,1,1,3,8,10,10,10-Octachlorodecane 100 96.4 Chiron AS 1623.11-100-IO 1,1,1,3,9,11,11,11-Octachloroundecane 100 99.9 Chiron AS 1624.12-100-IO 1,1,1,3,10,12,12,12-Octachlorododecane 100 97.7 Chiron AS 1625.13-100-IO 1,1,1,3,11,13,13,13-Octachlorotridecane 100 99.9 Chiron AS 1678.14-K-IO 1,1,1,3,12,14,14,14-Octachlorotetradecane 1000 N.A. Chiron AS 1671.10-100-IO 1,2,9,10-Tetrachlorodecane 100 95.4 Chiron AS 1674.11-100-IO 1,2,10,11-Tetrachloroundecane 100 N.A. Chiron AS 1677.14-K-IO 1,2,13,14-Tetrachlorotetradecane 1000 N.A. Chiron AS 12285.11-100-IO 1,2,3,4,5,6-Hexachloroundecane 100 62.5 Chiron AS 12728.11-100-IO 4,5,7,8- Tetrachloroundecane 100 89.4 Chiron AS 12590.10-100-IO 2,3,4,5-Tetrachlorodecane 100 71.6 Chiron AS 12425.12-100-IO 2,3,4,5-Tetrachlorododecane 100 67.1 CIL CIL-ULM-8917-1.2 1,5,5,6,6,10-Hexachlorodecane 100 95 Chiron AS 1659.10-100-IO 1,1,1,3,9,10-Hexachlorodecane 100 96.3 Chiron AS 1650.11-100-IO 1,1,1,3,10,11-Hexachloroundecane 100 99.9 Chiron AS 1652.12-100-IO 1,1,1,3,11,12-Hexachlorododecane 100 99.9 Chiron AS 1654.13-100-IO 1,1,1,3,12,13-Hexachlorotridecane 100 95
Table S2. System parameters e, a, s, l and c, and SD and R2 for the columns in this study calculated using
reference compounds. Values in parentheses are standard errors.
System parameters
Compounds e a s l c SD R2
SPB-Octyl 126 (±8) 0 0 202 (±1) 60 (±21) 36 0.997
HP-5ms 8 (±16) 212 (±27) 73 (±48) 203 (±1) 7 (±21) 39 0.996
DB-17ms 113 (±23) 401 (±40) 155 (±72) 205 (±2) -15 (±29) 59 0.994
InertCap-17ms 123 (±26) 438 (±46) 175 (±84) 205 (±2) -33 (±35) 62 0.993
DB-225ms 81 (±20) 644 (±31) 507 (±55) 206 (±2) -11 (±27) 44 0.994
SolGel-WAX 143 (±18) 691 (±29) 779 (±52) 203 (±2) 14 (±24) 41 0.995
Table S3a. The ppLFER solute descriptors for CPs whereof data was available from all columns (with an exception for 1,5,5,6,6,10-C10Cl6, which
was not detected on the SolGel-WAX). E values for CPs were obtained from the UFZ database and L was calculated using the SPB-Octyl column. A
and S values were calculated using either all columns without the DB-225ms column or without the SolGel-WAX column (see text for more
details). E, A, S and L values for n-alcohols, n-alkylmethyl esters, n-alkanes and PAHs were obtained from the UFZ database. (N.A., not available)
Compounds E A
(without SolGel-WAX) A
(without DB-225ms) S
(without SolGel-WAX) S
(without DB-225ms) L
1,1,1,3,10,11-C11Cl6 0.85 1.062 (±0.148) 0.353 (±0.091) 0.417 (±0.092) 0.692 (±0.080) 10.104
1,1,1,3,11,12-C12Cl6 0.85 1.092 (±0.139) -1.10 (±0.119) 0.392 (±0.086) 1.241 (±0.104) 10.674
1,1,1,3,12,13-C13Cl6 0.85 1.086 (±0.198) -1.11 (±0.150) 0.404 (±0.124) 1.256 (±0.131) 11.190
1,1,1,3,8,10,10,10-C10Cl8 1.04 1.124 (±0.165) -1.08 (±0.136) 0.370 (±0.103) 1.227 (±0.119) 10.679
1,1,1,3,9,10-C10Cl6 0.85 1.119 (±0.130) 0.391 (±0.083) 0.393 (±0.081) 0.676 (±0.073) 9.558
1,1,1,3-C10Cl4 0.52 0.267 (±0.026) 0.055 (±0.018) 0.323 (±0.016) 0.406 (±0.016) 7.483
1,1,1,3-C11Cl4 0.52 0.231 (±0.019) 0.040 (±0.014) 0.357 (±0.011) 0.432 (±0.012) 7.975
1,1,1,3-C12Cl4 0.52 0.297 (±0.032) 0.060 (±0.022) 0.315 (±0.020) 0.407 (±0.019) 8.524
1,1,1,3-C13Cl4 0.52 0.337 (±0.070) 0.079 (±0.039) 0.290 (±0.043) 0.390 (±0.034) 9.030
1,2,10,11-C11Cl4 0.65 1.079 (±0.086) 0.405 (±0.059) 0.413 (±0.054) 0.675 (±0.051) 8.978
1,2,3,4,5,6-C11Cl6 1.14 0.725 (±0.062) -0.03 (±0.015) 0.565 (±0.039) 0.858 (±0.013) 9.338
1,2,5,6,9,10-C10Cl6 0.99 1.787 (±0.107) 0.656 (±0.080) 0.455 (±0.067) 0.893 (±0.069) 9.898
1,2,9,10-C10Cl4 0.65 1.049 (±0.077) 0.411 (±0.054) 0.429 (±0.048) 0.677 (±0.047) 8.424
1,5,5,6,6,10-C10Cl6 0.81 1.045 (±0.000) N.A. 0.647 (±0.000) N.A. 10.054
2,3,4,5,6,7,8,9-C10Cl8 1.56 0.373 (±0.202) -0.11 (±0.098) 0.782 (±0.126) 0.968 (±0.085) 9.551
2,3,4,5-C10Cl4 0.74 0.398 (±0.084) 0.042 (±0.036) 0.454 (±0.052) 0.590 (±0.031) 7.433
2,3,4,5-C12Cl4 0.74 0.381 (±0.085) 0.028 (±0.038) 0.454 (±0.053) 0.590 (±0.033) 8.490
2,5,6,9-C10Cl4 0.59 1.092 (±0.051) 0.333 (±0.715) 0.420 (±0.031) 0.714 (±0.037) 7.930
4,5,7,8-C11Cl4 0.65 0.720 (±0.088) 0.129 (±0.038) 0.347 (±0.055) 0.575 (±0.033) 7.946
Table S3b. The solute descriptors E, A, S and L for the reference compounds used for the determination of system parameters for the GC-
columns in this study. Compound E A S L Compound E A S L
C8OH 0.2 0.37 0.42 4.619 C6OOC 0.08 0 0.6 3.874
C10OH 0.19 0.37 0.42 5.628 C8OOC 0.07 0 0.6 4.838
C12OH 0.18 0.37 0.42 6.62 C10OOC 0.05 0 0.6 5.803
C16OH 0.15 0.37 0.42 8.654 C12OOC 0.04 0 0.6 6.767
C18OH 0.15 0.37 0.42 9.662 C14OOC 0.03 0 0.6 7.731
C20OH 0.14 0.37 0.42 10.667 C16OOC 0.02 0 0.6 8.695
Decane 0 0 0 4.686 C18OOC 0.01 0 0.6 9.659
Undecane 0 0 0 5.191 C20OOC 0 0 0.6 10.75
Dodecane 0 0 0 5.696 C22OOC 0.05 0 0.6 11.82
Tridecane 0 0 0 6.2 C24OOC 0.05 0 0.6 12.824
Tetradecane 0 0 0 6.705 Naphthalene 1.23 0 0.91 5.157
Pentadecane 0 0 0 7.209 Acenaphthylene 1.55 0 1.13 6.395
Hexadecane 0 0 0 7.714 Acenaphthene 1.45 0 0.95 6.709
Heptadecane 0 0 0 8.218 Fluorene 1.66 0 1.1 6.948
Octadecane 0 0 0 8.722 Phenanthrene 1.92 0 1.28 7.712
Nonadecane 0 0 0 9.226 Anthracene 1.98 0 1.28 7.735
Eicosane 0 0 0 9.731 Fluoranthene 2.35 0 1.48 8.733
Henicosane 0 0 0 10.236 Pyrene 2.24 0 1.48 8.974
Docosane 0 0 0 10.74 Benz[a]anthracene 2.74 0 1.68 10.124
Tricosane 0 0 0 11.252 Chrysene 2.65 0 1.67 10.123
Tetracosane 0 0 0 11.758 Benzo[b]fluoranthene 3.19 0 1.82 11.632
Pentacosane 0 0 0 12.264 Benzo[k]fluoranthene 3.19 0 1.91 11.607
Hexacosane 0 0 0 12.77 Benzo[a]pyrene 3.02 0 1.85 11.54
Heptacosane 0 0 0 13.276
Octacosane 0 0 0 13.78
Nonacosane 0 0 0 14.291
Triacontane 0 0 0 14.794
Table S4. Weighted mean and range of RI values of n-alcohols, n-alkylmethyl esters, PAHs and CPs for SPB-Octyl, HP-5ms, DB-17ms, InertCap-
17ms, DB-225ms and SolGel-WAX colums. (N.A., not available) Compounds (number of possible diastereomers)
SPB-Octyl HP-5ms DB-17ms InertCap-17ms DB-225ms SolGel-WAX
Measured RI Predicted RI Measured RI Predicted RI Measured RI Predicted RI Measured RI Predicted RI Measured RI Predicted RI Measured RI Predicted RI
C8OH 1015 1113 1068 1073 1174 1120 1106 1392 1205 1551 1413
C10OH 1220 1305 1272 1276 1382 1314 1388 1304 1604 1424 1755 1658
C12OH 1425 1496 1474 1474 1587 1508 1595 1507 1817 1633 1958 1863
C16OH 1836 1895 1882 1881 2000 1909 2009 1920 2247 2040 2370 2294
C18OH 2041 2104 2085 2087 2207 2119 2218 2136 2459 2245 2577 2486
C20OH 2245 2295 2289 2287 2410 2312 2434 2329 2673 2499 2786 2674
C8OOC 1071 1124 1123 1121 1226 1158 1229 1180 1347 1228 1393 1351
C10OOC 1273 1301 1324 1306 1427 1341 1446 1360 1556 1437 1596 1534
C12OOC 1474 1511 1525 1514 1628 1553 1644 1574 1765 1659 1802 1762
C14OOC 1675 1741 1726 1734 1836 1771 1847 1792 1975 1864 2008 1981
C16OOC 1876 1927 1927 1927 2040 1964 2050 1984 2186 2080 2215 2214
C18OOC 2076 2130 2128 2127 2243 2167 2254 2187 2397 2268 2421 2385
C20OOC 2277 2317 2330 2318 2447 2351 2458 2367 2607 2562 2630 2612
C22OOC 2477 2514 2531 2522 2652 2571 2662 2597 2816 2664 2838 2798
C24OOC 2678 2686 2733 2697 2856 2728 2868 2739 3023 2943 3043 2985
Naphthalene 1206 1198 1193 1156 1420 1420 1431 1214 1615 1288 1754 1469
Acenaphthylene 1489 1457 1463 1403 1767 1455 1795 1482 2048 1643 2209 1878
Acenaphthene 1529 1436 1498 1385 1796 1431 1827 1459 2027 1577 2156 1769
Fluorene 1630 1553 1598 1488 1914 1542 1951 1577 2196 1687 2353 1931
Phenanthrene 1854 1830 1800 1746 2192 1816 2247 1852 2571 2040 2747 2381
Anthracene 1865 1815 1810 1733 2206 1802 2257 1837 2578 2012 2752 2347
Fluoranthene 2163 2057 2087 1950 2569 2036 2644 2091 3010 2299 3221 2704
Pyrene 2236 2052 2143 1940 2667 2027 2749 2082 3090 2290 3319 2694
Benz[a]anthracene N.A. 2316 2486 2255 3088 2337 3186 2391 N.A. 2596 N.A. 3000
Chrysene N.A. 2426 2497 2304 3127 2396 3216 2458 N.A. 2713 N.A. 3253
Benzo[b]fluoranthene N.A. 2543 2812 2392 3499 2488 3587 2564 N.A. 2718 N.A. 3294
Benzo[k]fluoranthene N.A. 2528 2820 2387 3513 2480 3596 2552 N.A. 2750 N.A. 3267
Benzo[a]pyrene N.A. 2550 2906 2392 3647 2490 3724 2569 N.A. 2721 N.A. 3302
Dibenzo[ah]anthracene N.A. 2896 3224 2798 N.A. 2908 4072 2969 N.A. 3229 N.A. 3839
Indeno[1,2,3-cd]pyrene N.A. 2729 3232 2675 N.A. 2770 N.A. 2831 N.A. 3074 N.A. 3572
Benzo[ghi]perylene N.A. 2753 3290 2695 N.A. 2795 4179 2859 N.A. 3105 N.A. 3613
Table S4. (Continued)
Compounds (nmber of diastereomers)
SPB-Octyl HP-5ms DB-17ms InertCap-17ms DB-225ms SolGel-WAX
Measured RI Predicted RI Measured RI Predicted RI Measured RI Predicted RI Measured RI Predicted RI Measured RI Predicted RI Measured RI Predicted RI
1,1,1,3,9,10-C10Cl6 (4) 2089
(2089 - 2089) 2143
(2104 - 2161) 2091
(2091 - 2091) 2115
(2078 - 2132) 2370
(2286 - 2396) 2389
(2342 - 2410) 2406
(2406 - 2406) 2427
(2377 - 2450) 2838
(2838 - 2838) 2796
(2732 - 2826) 2838
(2838 - 2839) 2868
(2808 - 2895)
1,1,1,3,10,11-C11Cl6 (4) 2199
(2148 - 2204) 2247
(2213 - 2272) 2199
(2146 - 2202) 2236
(2200 - 2264) 2488
(2404 - 2488) 2508
(2467 - 2541) 2516
(2443 - 2522) 2546
(2502 - 2582) 2937
(2846 - 2950) 2947
(2858 - 3011) 2931
(2830 - 2949) 2973
(2900 - 3034)
1,1,1,3,11,12-C12Cl6 (4) 2314
(2260 - 2315) 2319
(2302 - 2358) 2314
(2314 - 2314) 2322
(2309 - 2357) 2595
(2493 - 2631) 2593
(2571 - 2641) 2630
(2354 - 2636) 2632
(2608 - 2685) 3053
(2959 - 3057) 3030
(2999 - 3089) N.A.
3031 (2981 - 3117)
1,1,1,3,12,13-C13Cl6 (4) 2418
(2369 - 2421) 2415
(2400 - 2457) 2407
(2163 - 2423) 2420
(2407 - 2456) 2709
(2562 - 2743) 2706
(2687 - 2757) 2743
(2628 - 2751) 2751
(2730 - 2801) 3163
(3067 - 3168) 3126
(3103 - 3188) N.A.
3134 (3106 - 3207)
1,1,1,3,14,15-C15Cl6 (4) 2633
(2633 - 2633) 2639
(2625 - 2664) 2627
(2376 - 2663) 2638
(2612 - 2683) 2930
(2858 - 2969) 2961
(2942 - 2993) 2976
(2850 - 3020) 3002
(2983 - 3036) N.A.
3352 (3317 - 3413)
N.A. 3332
(3295 - 3399)
1,1,1,3,8,10,10,10-C10Cl8 (3) 2322
(2322 - 2322) 2327
(2305 - 2340) 2309
(2309 - 2324) 2312
(2293 - 2324) 2590
(2381 - 2627) 2593
(2569 - 2607) 2644
(2644 - 2644) 2621
(2596 - 2637) 3061
(3061 - 3061) 3050
(3026 - 3064) N.A.
3097 (3066 - 3116)
1,1,1,3,9,11,11,11-C11Cl8 (3) 2437
(2437 - 2437) 2403
(2393 - 2419) 2425
(2409 - 2443) 2393
(2384 - 2410) 2715
(2499 - 2752) 2683
(2672 - 2704) 2758
(2585 - 2808) 2719
(2707 - 2739) N.A.
3126 (3112 - 3144)
N.A. 3177
(3159 - 3195)
1,1,1,3,10,12,12,12-C12Cl8 (3) 2546
(2546 - 2546) 2545
(2512 - 2564) 2526
(2272 - 2540) 2523
(2502 - 2536) 2763
(2763 - 2763) 2858
(2828 - 2875) 2883
(2693 - 2889) 2911
(2878 - 2931) N.A.
3285 (3262 - 3297)
N.A. 3319
(3298 - 3331)
1,1,1,3,11,13,13,13-C13Cl8 (3) 2654
(2654 - 2654) 2652
(2648 - 2655) 2620
(2381 - 2651) 2639
(2633 - 2646) 2955
(2927 - 3009) 2971
(2967 - 2976) 2958
(2686 - 3046) 3009
(3004 - 3013) N.A.
3396 (3388 - 3402)
N.A. 3414
(3408 - 3420)
1,1,1,3,12,14,14,14-C14Cl8 (3) 2764
(2764 - 2764) 2751
(2718 - 2793) 2746
(2490 - 2762) 2774
(2747 - 2807) 3065
(2780 - 3108) 3100
(3060 - 3148) 3116
(2994 - 3160) 3142
(3101 - 3192) N.A.
3554 (3507 - 3611)
N.A. 3552
(3509 - 3607)
1,1,1,3-C10Cl4 (2) 1622
(1606 - 1856) 1606
(1606 - 1606) 1615
(1615 - 1615) 1615
(1615 - 1615) 1734
(1734 - 1849) 1748
(1748 - 1748) 1749
(1749 - 1749) 1760
(1760 - 1760) 1906
(1828 - 2094) 1918
(1918 - 1918) 1916
(1908 - 1917) 1866
(1866 - 1866)
1,1,1,3-C11Cl4 (2) 1721
(1651 - 1723) 1723
(1723 - 1723) 1721
(1721 - 1721) 1734
(1734 - 1734) 1844
(1763 - 1844) 1885
(1885 - 1885) 1856
(1856 - 1856) 1899
(1899 - 1899) 2011
(1930 - 2012) 2054
(2054 - 2054) 2022
(1994 - 2024) 2010
(2010 - 2010)
1,1,1,3-C12Cl4 (2) 1832
(1800 - 1896) 1819
(1819 - 1820) 1826
(1826 - 1826) 1843
(1842 - 1844) 1948
(1755 - 2063) 1999
(1998 - 2000) 1965
(1939 - 2036) 2012
(2010 - 2013) 2130
(2053 - 2315) 2183
(2180 - 2186) 2132
(2132 - 2132) 2132
(2128 - 2136)
1,1,1,3-C13Cl4 (2) 1934
(1913 - 1935) 1908
(1908 - 1908) 1932
(1932 - 1932) 1934
(1934 - 1934) 2036
(1955 - 2036) 2106
(2106 - 2106) 2072
(2072 - 2072) 2122
(2122 - 2122) 2238
(2220 - 2239) 2319
(2319 - 2319) 2237
(2208 - 2240) 2232
(2232 - 2232)
1,1,1,3-C14Cl4 (2) 2042
(2042 - 2042) 2029
(2025 - 2032) 2038
(1941 - 2111) 2051
(2048 - 2053) 2162
(1966 - 2264) 2245
(2242 - 2248) 2183
(1979 - 2291) 2266
(2263 - 2269) N.A.
2468 (2464 - 2472)
N.A. 2333
(2330 - 2337)
1,2,9,10-C10Cl4 2) 1853
(1802 - 1855) 1890
(1887 - 1893) 1876
(1876 - 1876) 1894
(1893 - 1896) 2132
(2065 - 2132) 2105
(2101 - 2109) 2167
(2167 - 2167) 2141
(2138 - 2145) 2590
(2314 - 2601) 2500
(2492 - 2509) 2617
(2507 - 2621) 2558
(2542 - 2574)
Table S4. (Continued) Compounds SPB-octyl HP5 DB17 Inert17 DB225 WAX Measured RI Predicted RI Measured RI Predicted RI Measured RI Predicted RI Measured RI Predicted RI Measured RI Predicted RI Measured RI Predicted RI
1,2,10,11-C11Cl4 (2) 1965
(1918 - 1987) 2014
(2007 - 2020) 1985
(1931 - 2158) 2008
(2002 - 2014) 2247
(2177 - 2283) 2248
(2240 - 2257) 2277
(2277 - 2277) 2291
(2282 - 2299) 2708
(2615 - 2787) 2624
(2614 - 2634) 2724
(2620 - 2785) 2664
(2653 - 2675)
1,2,13,14-C14Cl4(2) 2296
(2296 - 2296) 2282
(2278 - 2286) 2312
(2309 - 2485) 2304
(2300 - 2308) 2578
(2578 - 2809) 2551
(2546 - 2557) 2645
(2388 - 2857) 2590
(2583 - 2597) N.A.
2921 (2907 - 2935)
N.A. 2883
(2874 - 2891)
2,5,6,9-C10Cl4 (6) 1740
(1734 - 1745) 1748
(1639 - 1820) 1782
(1769 - 1787) 1754
(1645 - 1825) 2022
(2014 - 2031) 1958
(1839 - 2035) 2053
(2043 - 2059) 1992
(1874 - 2068) 2495
(2437 - 2511) 2343
(2196 - 2456) 2467
(2421 - 2482) 2421
(2306 - 2537)
4,5,7,8-C11Cl4 (6) 1757
(1738 - 1761) 1741
(1678 - 1778) 1774
(1749 - 1782) 1751
(1698 - 1787) 1934
(1908 - 1954) 1931
(1869 - 1969) 1970
(1962 - 1981) 1955
(1895 - 1992) 2272
(2212 - 2290) 2197
(2117 - 2251) 2231
(2165 - 2256) 2250
(2187 - 2291)
1,2,5,6,9,10-C10Cl6 (6) 2199
(2199 - 2200) 2274
(2229 - 2300) 2231
(2229 - 2231) 2243
(2196 - 2282) 2605
(2598 - 2605) 2560
(2501 - 2594) 2659
(2659 - 2659) 2597
(2532 - 2640) 3314
(3314 - 3314) 3140
(3053 - 3185) 3312
(3311 - 3313) 3267
(3167 - 3322)
2,3,4,5,6,7,8,9-C10Cl8 (72) 2181
(2177 - 2199) 2153
(2031 - 2307) 2201
(2199 - 2213) 2171
(2041 - 2335) 2461
(2461 - 2461) 2419
(2263 - 2610) 2525
(2525 - 2525) 2480
(2293 - 2692) 2773
(2769 - 2817) 2851
(2587 - 3127) 2756
(2754 - 2770) 2956
(2622 - 3300)
1,2,3,4,5,6-C11Cl6 (16) 2088
(2030 - 2114) 2006
(1936 - 2109) 2101
(1918 - 2253) 2040
(1961 - 2104) 2366
(2245 - 2391) 2254
(2150 - 2348) 2391
(2339 - 2431) 2308
(2181 - 2389) 2734
(2587 - 2842) 2609
(2454 - 2695) 2639
(2500 - 2733) 2665
(2447 - 2780)
2,3,4,5-C10Cl4 (6) 1656
(1612 - 1677) 1654
(1539 - 1704) 1667
(1619 - 1692) 1662
(1557 - 1699) 1841
(1750 - 1856) 1820
(1680 - 1878) 1844
(1773 - 1884) 1841
(1694 - 1893) 2075
(1915 - 2162) 2042
(1847 - 2119) 2074
(1925 - 2148) 2092
(1819 - 2203)
2,3,4,5-C12Cl4 (6) 1868
(1827 - 1890) 1842
(1757 - 1891) 1875
(1831 - 1900) 1868
(1783 - 1905) 2060
(1962 - 2060) 2041
(1930 - 2103) 2055
(1987 - 2095) 2062
(1946 - 2121) 2283
(2142 - 2387) 2298
(2089 - 2401) 2276
(2141 - 2355) 2292
(2054 - 2418)
1,5,5,6,6,10-C10Cl6 (1) 2190
(2190 - 2190) 2226
(2226 - 2226) 2214
(2214 - 2214) 2209
(2209 - 2209) 2566
(2566 - 2566) 2489
(2489 - 2489) 2619
(2619 - 2619) 2544
(2544 - 2544) 3065
(3065 - 3065) 2965
(2965 - 2965) N.A.
2998 (2998 - 2998)
Figure S1. Chromatograms of several CP standards on the SPB-Octyl column (A,B,D,E) and the SolGel-WAX column (C,F).
Figure S2. RI values against carbon chain length for n-alcohols, n-alkylmethyl esters and 4 groups of CPs
with different chlorination patterns.
Figure S3. Solute descriptors for a selection of CPs calculated using measured RI values from all columns
in this study (including both DB-225ms and SolGel-WAX). Error bars indicate the standard errors from
multiple linear regression analysis.
1,1,
1,3-
C 10Cl 4
2,3,
4,5-
C 10Cl 4
4,5,
7,8-
C 11Cl 4
2,5,
6,9-
C 10Cl 4
1,2,
9,10
-C10Cl 4
1,2,
3,4,
5,6-
C 11Cl 6
2,3,
4,5,
6,7,
8,9-
C 10Cl 8
1,1,
1,3,
9,10
-C10Cl 6
1,2,
5,6,
9,10
-C10Cl 6
-0.5
0.0
0.5
1.0
1.5
2.0
7
8
9
10
11
Des
cri
pto
r v
alu
e (
E,
A a
nd
S
)D
es
crip
tor v
alu
e (L
)
E descriptor
A descriptor
L descriptor
S descriptor
Figure S4. Predicted RI values from COSMO-RS vs measured RI values for all compounds. The vertical
and horizontal error bars show the range of measured RIs for multiple peaks.
Figure S5. Predicted RI values with corrections vs measured RI values for CPs. The vertical and horizontal
error bars show the range of measured RIs for multiple peaks.
Figure S6. Calculated log Kair/polymer partition coefficients from COSMOthermX versus the elution
temperature. Panel A shows how the elution temperatures obtained from the retention time and the
applied GC temperature program were used to derive the partition coefficient for the reference
compounds. Panel B shows how the average Kair/polymer partition coefficient is used to back-calculate the
elution temperature for each compound.
Figure S7a. Mass spectra of (A) 1,1,1,3-C10Cl4, (B) 2,5,6,9-C10Cl4, (C) 1,2,9,10-C10Cl4, and (D) 1,1,1,3,9,10-
C10Cl6 obtained by GC-APCI-TOF-MS analysis.
m/z
m/z
m/z
m/z
[M-Cl]+
[M-2H-2Cl]+
[M-2H-3Cl]+
[M-H-Cl]+[M-2H-2Cl]+
[M-2H-3Cl]+
[M-Cl]+
[M-2H-2Cl]+[M-2H-3Cl]+
[M+H3O]+
[M-H-Cl]+[M-H-2Cl]+
[M-2H-3Cl]+
[M-3H-4Cl]+
A
B
C
D
Figure S7b. Mass spectra of (E) 1,2,5,6,9,10-C10Cl6, (F) 1,5,5,6,6,10-C10Cl6, (G) 1,1,1,3,8,10,10,10-C10Cl8,
and (H) 2,3,4,5,6,7,8,9-C10Cl8 obtained by GC-APCI-TOF-MS analysis.
m/z
m/z
m/z
m/z
[M-H-Cl]+
[M-H-2Cl]+[M-2H-3Cl]+
[M-H-Cl]+
[M-H-2Cl]+
[M-2H-3Cl]+
[M-3H-4Cl]+
[M-H-Cl]+[M-2H-2Cl]+
[M-2H-3Cl]+
[M-3H-4Cl]+
[M-H-Cl]+
[M-H-2Cl]+
[M-2H-3Cl]+
E
F
G
H
Figure S8. Relationship between abundances of CP isomer peaks and values of (A) fragmentor voltage,
(B) capillary voltage, (C) corona current, and (D) gas temperature of APCI-TOF-MS system.
0
2000
4000
6000
8000
10000A
bu
nd
ance
Fragmentor (V)
A
0
2000
4000
6000
8000
10000
Ab
un
dan
ce
Capillary voltage (V)
B
0
2000
4000
6000
8000
10000
12000
Ab
un
dan
ce
Corona current (μA)
C
0
2000
4000
6000
8000
10000
12000
14000
16000
Ab
un
dan
ce
Gas temperature (°C)
D
1,1,1,3-C10Cl4
2,5,6,9-C10Cl4
1,2,9,10-C10Cl4
1,1,1,3,9,10-C10Cl6
1,2,5,6,9,10-C10Cl6
1,5,5,6,6,10-C10Cl6
1,1,1,3,8,10,10,10-C10Cl8
Reference
1. Curvers, J., Rijks, J., Cramers, C., Knauss, K. & Larson, P. Temperature programmed retention indices:
Calculation from isothermal data. Part 1: Theory. J. High Resolut. Chromatogr. 8, 607–610 (1985).
download fileview on ChemRxiv20200803-CPs_GC-COSMO_Hammer-Endo_SI.pdf (1.50 MiB)
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