Determination of carbonyl compounds from Determination of carbonyl compounds from monoterpene oxidation using the IfT chambermonoterpene oxidation using the IfT chamber
Ariane Kahnt
23.06.2008
Leibniz-Institut für Troposphärenforschung
Permoserstr. 15
04318 Leipzig, Germany
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Content
1. Introduction
2. Experimental
3. Method development for carbonyl compound analysis
4. In-situ derivatisation of carbonyl compounds on DNPH-
coated denuders
5. First results from gas- and particle-phase analysis
6. Further improvement
7. Summary
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Introduction
- Monoterpenes are biogenic volatile organic compounds (BVOC)
- Emission from various plants and coniferyl trees
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Introduction
- Estimated global emission of volatile organic compounds (VOC): 1150 Tg C/year (Guenther et al. 1995): comprised of
- 44 % isoprene
- 11 % monoterpenes
- BVOC emission exceed those of anthropogenic compounds by a factor of ~10.
- Most BVOCs are more reactive than many anthropogenic non-methane volatile organic compounds (NMVOC)
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Introduction
Monoterpenes
- C10H16-skeleton
-pinene -pinene limonene 3-carene camphene sabinene
- Act as repellent, Pheromone for insects
- Most abundant monoterpenes emitted are -pinene, -pinene and limonene
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Introduction
- Atmospheric degradation of monoterpenes includes reactions with NO3, OH radicals and O3
- Oxidation leads to multifunctional oxidation products with low vapour pressure
- Their condensation and coagulation-processes lead to particle formation / growth (formation of secondary organic aerosol = SOA)
- SOA scatters solar radiation and can act as cloud condensation nuclei
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Introduction
Challenge:
- SOA formation is complex and not well known
- Composition of SOA is largely unknown
Motivation:
- Emission of BVOC is driven by climate (temperature, light)- Atmospheric oxidation leads to products that effect climate - Get more information about the oxidative decomposition of
monoterpenes
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Introduction
- Monoterpene oxidation produces semivolatiles and (or) multifunctional compounds such as carbonyl compounds and caboxylic acids
- Carbonyls play an important role in photochemical reactions
- Carbonyl compounds undergo photolysis and react with OH and NO3
radicals
- Some of them partition between the gas- and particle-phases
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Introduction
Mainly first oxidation products from monoterpenes are oxo-compounds(aldheydes and ketones)
Their reactions are not well characterised
- What are the next oxidation products?- What are their yields?- What are the mechanisms?
The challenge is:
- Carbonyl compounds are hard to sample and analyse
- Not all reaction products are available for positive identification and quantification
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Introduction
Examples of aldehydes originating from monoterpenesExamples of aldehydes originating from monoterpenes
Campholenic aldehyde
Endolim (from limonene)
Nopinon (from β-pinene)
Pinonaldehyde (from -pinene)
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Experimental
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Experimental
Aerosol chamber at the IfT (LEAK – „Leipziger Aerosol Kammer“)
- Overall chemistry in the atmosphere is far complex- Chamber studies provide a better understanding of atmospheric
reactions - Controlled parameters
LEAK („Leipziger Aerosol Kammer“ at the IfT)
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Experimental
Characteristics of the IfT chamber
- Made of Teflon® foil
- Cylindrical geometry
- Volume: 19 m3
- Surface/volume ratio: 2.1 m-1
- 60 UV-lamps
- Thermostat
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Experimental
Analysis of carbonyl compounds
- Polar carbonyl group
- Some carbonyls can partially or completely pass the sampling or analytical technique
- Derivatisation is necessary: e.g. with 2,4-Dinitrophenylhydrazine (DNPH)
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Experimental
- DNPH is a derivatisation reagent for aldehyde- and keto-groups
- Precipitation reagent
- Well known method for the identification of aldehydes and ketons by the melting points of the formed hydrazones (Brady 1931; Allen 1937)
- The formed hydrazones are:
- Coloured. This makes them detectable with UV-spectroscopy
- Easily ionisable using electrospray ionisation (ESI). This makes them detectable with HPLC/ESI-MS.
solution of DNPH addition of a carbonyl compound
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Experimental
Analysis of the hydrazones:
HPLC-UV coupled with ESI-TOFMS
HPLC (high performance liquid chromatography):
- Separation of compounds based on their distribution between a stationary phase (column) and a mobile phase (eluent)
- Depending on their affinity to the phases. The compounds are eluted at certain time
ESI-TOFMS (Electrospray Ionisation Time-Of-Flight Mass Spectrometry) - Ionisation of the compounds by electrospray- Formed ions are accelerated in an electric field - The velocity of ions depends on mass to charge ratios (m/z); hence the
mass to charge ratios of the analyte ions can be calculated from the time required for the ions to reach a detector
- TOF-MS is a high resolution mass spectrometer
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Experimental
First Step
Method development for standard compounds
- Available or synthesised monoterpene oxidation products were derivatised:
- Campholenic aldehyde- Endolim- Nopinone- Pinonaldehyde
to form the respective hydrazone
- Analysis and characterisation with HPLC/ESI-TOFMS
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Results from the method development of
carbonyl compound analysis
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Method development for carbonyl analysis
Hydrazone standard Structure M [g/mol]
Benzaldehyde-DNPH
C13H10N4O4
286
Campholenic aldehyde-DNPH
C16H20N4O4
332
Endolim-di-DNPH
C22H24N8O8
528
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Method development for carbonyl analysis
Hydrazone standard Structure M [g/mol]
Nopinon-DNPH
C15H18N4O4
318
Pinonaldehyde-di-DNPH
C22H24N8O8
528
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Method development for carbonyl analysis
Standard-Hydrazone-Mix
Benzaldehyde (m/z 285), Pinonaldehyde (m/z 527)
Nopinon (m/z 317), Campholenic aldehyde (m/z 331), Endolim (m/z 527)
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Method development for carbonyl analysis
Characterisation of the analytical method
Hydrazone standard RT
[min]
R2 LOD
[g/ml]
RSD
[%]
Benzaldehyde 11.4 0.9979 0.012 2.49
Campholenic aldehyde
14.2 0.9970 0.024 3.56
Endolim 15.1 0.9956 0.097 9.53
Nopinon 13.5 0.9993 0.072 2.87
Pinonaldehyde 15.1 0.9943 0.005 8.71
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Method development for carbonyl analysis
Suitable method regarding:
- chromatographic separation
(except the isobaric hydrazones of endolim and pinonaldehyde)- sensitivity
- stability
TOFMS allows the determination of exact chemical formula also for
unknown compounds due to its high sensitivity
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Method development for carbonyl analysis
- To collect also small carbonyl compounds which can not be collected with resin based denuder-sampling, on-tube derivatisation is performed
Use of annular denuders:
Advantages:
- Larger sampling capacity
- Operate at higher sample flow rates
Disadvantage:
- Diffusion equation not
characterised
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Method development for carbonyl analysis
Coated Denuders
- With the adsorbent XAD-4 as a collection surface
- Additional with DNPH + H3PO4 for the on-tube conversion of carbonyl compounds
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In-situ derivatisation of carbonyl compounds on DNPH-coated denuders
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In-situ derivatisation of carbonyl compounds on DNPH-coated denuders
- First compound: campholenic aldehyde
- Chamber experiments with different concentration of campholenic aldehyde
- Sampling with the DNPH-coated denuder
- Denuder extraction
- Analysis with the developed HPLC/ESI-TOFMS method
injected concentration [ppb]
10
40
80
160
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In-situ derivatisation of carbonyl compounds on DNPH-coated denuders
Gas-phase calibration of campholenic aldehyde on DNPH-coated denudersGas-phase calibration of campholenic aldehyde on DNPH-coated denuders
y = -2.3119x2 + 790.87x - 5040.1
R2 = 0.9971
0
10000
20000
30000
40000
50000
60000
70000
0 50 100 150 200
injected amount [ppb]
area
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- Cleaning procedure is necessary to remove the acid
- Should be done directly after the experiment
SPE (solid phase extraction)
OasisOasis®® HLB cartridges HLB cartridges
with a Hydrophilic-Lipophilic-Balanced sorbent
- Reversed phase polymer sorbent
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First results from gas- and particle-
phase analysis
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Results from gas- and particle-phase analysis
Chamber experiment -pinene
Initial HC concentration [ppb]
100
O3 60
RH [%] ~ 50
T [°C] 21±1
Reaction time [h] 2.5
Sampling time [h] 1
Seed particle NH4HSO4
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Results from gas- and particle-phase analysis
Filter Extract: particle-phase products
- Identification of the hydrazones from formaldehyde (m/z 209)
and pinonaldehyde (m/z 527)
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Results from gas- and particle-phase analysis
Denuder Extract: gas-phase products
- Identification of the hydrazones from formaldehyde (m/z 209), acetone (m/z 237) and pinonaldehyd (m/z 527)
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Results from gas- and particle-phase analysis
Preliminary quantitative result
Yield by mass References
Pinonaldehyde Gas-phase: 0.24
Particle-phase: 0.01
0.51±0.06 Hatakeyama et al. (1989)
0.19±0.04 Hakola et al. (1994)
0.06±0.19 Yu et al. (1999)
0.164±0.029 Baker et al. (2002)
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Further improvement
Further characterisation of in-situ derivatisation on denuders has to be
done to improve quantification:
- Denuder properties (e.g. variation between duty cycle, variability between different denuders)
- SPE method (recovery)
- More standards need to be prepared (HCHO, acetone etc...)
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Summary
- An HPLC-ESI-TOFMS method was developed for some first generation monoterpene oxidation products
(endolim, nopinon, pinonaldehyde)
- In-situ derivatistion on DNPH-coated denuders with campholenic aldehyde was performed and show a very good collection efficiency
- From the ozonolysis experiment of -pinene several carbonyl compounds were identified.
The yield of pinonaldehyde in the gas- and particle-phase was determined
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Acknowledgements
- Organiser of the summer school
- EUCAARI
(European Commission grant number 036833)
- IfT chamber team
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End
Thank You
very much
for your attention!
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Derivatisation with 2.4-Dinitrophenylhydrazine
- Gives coloured hydrazones (UV detection possible!)
- Detection at the wavelength near the absorption maxima of the respective hydrazone (360 nm)
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Oasis® HLB cartridges
- Contain a reversed phase sorbent (Hydrophilic-Lipophilic-Balanced)- Copolymer with aligned ratio of hydrophilic (N-Vinylpyrrolidone) and
lipophilic compound (Divinylbenzene)- Robust (pH)
General procedure:
- Coloumn solvation with methanol. water. acetonitrile- Coloumn conditioning with the sample medium- Sample loading- Coloumn washing with water- Target compound elution with acetonitrile
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Conditions for HPLC-UV-ESI-TOFMS analysis
Column Phenomenex® Gemini C6 Phenyl (3.5 µm.150 x 2 mm)
Eluents 0.2 % acetic acid in water (A)and 0.2 % acetic acid in acetonitrile (B) (programme: 70% A to 10% in 15 min)
Flow rate 0.5 ml/min
Sample injection 10 µl
Mass calibration 0.2 % acetic acid/5 mM NaOH in 50/50 (v/v %) in water/i-propanol solution at thebeginning of analysis
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