CATOME: Carbonyls in tropospheric oxidation mechanisms

• Unité de recherche: PCRD EU
• Numéro de projet: 97.0126
• Titre du projet anglais: CATOME: Carbonyls in tropospheric oxidation mechanisms

Mots-clé (Anglais)

Ambient air; photochemistry; formation; C5-C10 carbonyls; identification; mass spectrometry

Autre Numéro de projet (Anglais)

EU project number: ENV4-CT97-0416

Programme de recherche (Anglais)

EU-programme: 4. Frame Research Programme - 3.1 Environment

Description succincte (Anglais)

See abstract

Partenaires et organisations internationales (Anglais)

Coordinator:Norwegian Institute for Air Research (NO)

Résumé des résultats (Abstract) (Anglais)

High performance liquid chromatography (HPLC) combined with multiple mass spectrometry (MSn) in an ion trap was applied to identify carbonyl compounds in ambient air after its transfer to 2,4-dinitrophenylhydrazones (DNPH) during sampling. A developed structure elucidation scheme based on MSn spectra and the synthesis of model carbonyl derivatives among them 18 C6 carbonyl derivatives and 30 15N2-isotope-labelled derivatives allowed to identify completely or partially the structures of C5 to C10 carbonyls. These compounds are important for our understanding of photochemical degradation in the atmosphere. It was possible to differentiate aldehydes from ketones, branched from straight chain structures, aromatic from a-unsaturated carbonyls, as well as to identify other substructures such as branching points in aliphatic ketones. This identification scheme was applied to real air sam-ples where some unusual C6 ketones could be unequivocally identified. In addition, it allowed to elucidate more than 90 % of the structures (around 40) formed during degradation of a-pinene in a reaction chamber and to control the postulated master reaction scheme. It could also be shown that by-products were formed during the standard sampling and on-line derivatisation procedure. As a result of this work a compact disc was generated with the MSn spectra of several hundreds of carbonyl DNPH compounds, which can be made available on request. In addition, quantities of 0.2 to 1 g of 60 hitherto not available reference compounds (e.g. 18 C6-carbonyls and 30 15N2-labelled carbonyls) are on stock at the University of Basel.

Finally, a quantitative method for the determination of such carbonyl derivatives by LC-MS was developed and validated in detail (control of blanks, linearity etc.). The isotope-labelled 15N2-2-butanone-2,4-dinitrohydrazone was synthesised and applied as internal standard. The HPLC-MS was compared during an intercomparison exercise with other techniques such as gas chromatography-MS and HPLC-UV detection. Ambient air samples from a background region were quantified and a satisfactory agreement between the different techniques found despite the low levels observed. For HPLC-MS, detection limits for a 750 l air sample were between 0.08 and 0.3 mg/m3 which is comparable to the other methods. The structure elucidation scheme has been published in Anal. Chem. 70, 1979-1985 (1998). In addition, a manuscript about structure identification of the degradation products of a-pinene has been submitted to Atmos. Environ. and a paper about quantification will follow.

In conclusion, it could be shown that HPLC-MSn is a very promising tool for the identification and quantification of carbonyls in ambient air and formed in reaction chamber experiments. This technique si now applied in related projects.

Références bases de données (Anglais)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 97.0126