Monoterpene and sesquiterpene synthases and the origin of ...
Determination of carbonyl compounds from monoterpene oxidation using the IfT chamber Ariane Kahnt...
-
Upload
annabella-kelley -
Category
Documents
-
view
228 -
download
0
Transcript of Determination of carbonyl compounds from monoterpene oxidation using the IfT chamber Ariane Kahnt...
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
2/38
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
3/38
Introduction
- Monoterpenes are biogenic volatile organic compounds (BVOC)
- Emission from various plants and coniferyl trees
4/38
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)
5/38
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
6/38
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
7/38
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
8/38
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
9/38
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
10/38
Introduction
Examples of aldehydes originating from monoterpenesExamples of aldehydes originating from monoterpenes
Campholenic aldehyde
Endolim (from limonene)
Nopinon (from β-pinene)
Pinonaldehyde (from -pinene)
11/38
Experimental
12/38
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)
13/38
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
14/38
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)
15/38
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
16/38
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
17/38
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
18/38
Results from the method development of
carbonyl compound analysis
19/38
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
20/38
Method development for carbonyl analysis
Hydrazone standard Structure M [g/mol]
Nopinon-DNPH
C15H18N4O4
318
Pinonaldehyde-di-DNPH
C22H24N8O8
528
21/38
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)
22/38
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
23/38
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
24/38
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
25/38
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
26/38
In-situ derivatisation of carbonyl compounds on DNPH-coated denuders
27/38
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
28/38
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
29/38
- 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
30/38
First results from gas- and particle-
phase analysis
31/38
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
32/38
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)
33/38
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)
34/38
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)
35/38
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...)
36/38
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
37/38
Acknowledgements
- Organiser of the summer school
- EUCAARI
(European Commission grant number 036833)
- IfT chamber team
38/38
End
Thank You
very much
for your attention!
39/38
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)
40/38
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
41/38
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