Characterisation and optimisation of a sample preparation method for the detection and quantification of atmospherically relevant carbonyl compounds in aqueous medium

Abstract

Abstract. Carbonyl compounds are ubiquitous in the atmosphere and either emitted primarily from anthropogenic and biogenic sources or they are produced secondarily from the oxidation of volatile organic compounds. Despite a number of studies about the quantification of carbonyl compounds a comprehensive description of optimised methods is scarce for the quantification of atmospherically relevant carbonyl compounds. The method optimisation was conducted for seven atmospherically relevant carbonyl compounds including acrolein, benzaldehyde, glyoxal, methyl glyoxal, methacrolein, methyl vinyl ketone and 2,3-butanedione. O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) was used as derivatisation reagent and the formed oximes were detected by gas chromatography/mass spectrometry (GC/MS). With the present method quantification can be carried out for each carbonyl compound originating from fog, cloud and rain or sampled from the gas- and particle phase in water. Detection limits between 0.01 and 0.17 μmol L−1 were found, depending on carbonyl compounds. Furthermore, best results were found for the derivatisation with a PFBHA concentration of 0.43 mg mL−1 for 24 h followed by a subsequent extraction with dichloromethane for 30 min at pH = 1. The optimised method was evaluated in the present study by the OH radical initiated oxidation of 3-methylbutanone in the aqueous phase. Methyl glyoxal and 2,3-butanedione were found to be oxidation products in the samples with a yield of 2% for methyl glyoxal and 14% for 2,3-butanedione after a reaction time of 5 h.

A quantification method for heat-decomposable methylglyoxal oligomers and its application on 1,3,5-trimethylbenzene SOA

“…As this was observed for both types of samples, it appears that the pH influences the derivatisation and/or the oligomer decomposition. No influence of the pH on the PFBHA derivatisation reaction was reported by Rodigast et al (2015), indicating the effect of the pH is connected to thermal decomposition of the heatdecomposable oligomeric compounds. In summary, based on these results, pH = 1 was used.…”

“…The extract of one half of the filter was used for oligomer measurements (extract 1) and with the second one methylglyoxal monomers were quantified which were not a building block of oligomers (extract 2). A detailed description of the derivatisation procedure can be found in Rodigast et al (2015). Selected parameters given in bold.…”

“…The filters were prepared according to the method described by Rodigast et al (2015); thus, 300 µL of an aqueous PFBHA solution (5 mg mL −1 ) was added to the filter extracts. After a derivatisation time of 24 h at room temperature the derivatised methylglyoxal monomers were extracted.…”

“…After derivatisation of both filter extracts (extract 1 and 2), derivatised methylglyoxal was extracted at pH = 1 for 30 min with 250 µL of dichloromethane using an orbital shaker (1500 rpm; Rodigast et al, 2015). One microlitre of the organic phase was injected into GC/MS for analysis.…”

“…One filter extract was heated for 15 h and allowed to stand at room temperature for 9 h (sample A) to reach a total derivatisation time of 24 h (as it was optimised for PF-BHA derivatisation by Rodigast et al, 2015). To exclude reoligomerisation processes of methylglyoxal in sample A, one filter extract was heated for 15 h and measured directly after the heating process (sample B).…”