Transcript DBU Seminar 2007 - Paul Scherrer Institut

Determination of carbonyl compounds from
monoterpene oxidation using the IfT chamber
Ariane Kahnt
23.06.2008
Leibniz-Institut für Troposphärenforschung
Permoserstr. 15
04318 Leipzig, Germany
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
-
-
b-pinene
limonene
3-carene
camphene
sabinene
Act as repellent, Pheromone for insects
Most abundant monoterpenes emitted are -pinene, b-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 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
Benzaldehyde-DNPH
Structure
M [g/mol]
286
C13H10N4O4
Campholenic aldehydeDNPH
332
C16H20N4O4
Endolim-di-DNPH
528
C22H24N8O8
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Method development for carbonyl analysis
Hydrazone standard
Nopinon-DNPH
Structure
M [g/mol]
318
C15H18N4O4
Pinonaldehyde-diDNPH
528
C22H24N8O8
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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
R2
[min]
LOD
RSD
[mg/ml]
[%]
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
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First compound: campholenic aldehyde
Chamber experiments with different concentration of campholenic
aldehyde
injected concentration [ppb]
10
40
80
160
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Sampling with the DNPH-coated denuder
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Denuder extraction
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Analysis with the developed HPLC/ESI-TOFMS method
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In-situ derivatisation of carbonyl compounds on DNPH-coated denuders
Gas-phase calibration of campholenic aldehyde on DNPH-coated denuders
70000
60000
area
50000
40000
2
y = -2.3119x + 790.87x - 5040.1
30000
R2 = 0.9971
20000
10000
0
0
50
100
150
200
injected amount [ppb]
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Cleaning procedure is necessary to remove the acid
-
Should be done directly after the experiment
SPE (solid phase extraction)
Oasis® HLB cartridges
with a Hydrophilic-Lipophilic-Balanced sorbent
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Reversed phase polymer sorbent
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First results from gas- and particlephase analysis
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Results from gas- and particle-phase analysis
Chamber experiment
-pinene
Initial HC concentration
[ppb]
O3
100
RH [%]
~ 50
T [°C]
21±1
Reaction time [h]
2.5
Sampling time [h]
1
Seed particle
NH4HSO4
60
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Results from gas- and particle-phase analysis
Filter Extract: particle-phase products
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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
Pinonaldehyde
Yield by mass
References
Gas-phase: 0.24
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)
Particle-phase: 0.01
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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)
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SPE method (recovery)
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More standards need to be prepared
(HCHO, acetone etc...)
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Summary
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An HPLC-ESI-TOFMS method was developed for some first
generation monoterpene oxidation products
(endolim, nopinon, pinonaldehyde)
-
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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
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Organiser of the summer school
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EUCAARI
(European Commission grant number 036833)
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IfT chamber team
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End
Thank You
very much
for your attention!
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Derivatisation with 2.4-Dinitrophenylhydrazine
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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 the
beginning of analysis
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