Simultaneous determination of trace concentrations of aldehydes and carboxylic acids in particulate matter.

Carboxylic acids and aldehydes are present in ambient air particulate matter (PM) originating from both primary emission and secondary production in air and may, due to their polarity have, an impact on formation of cloud condensation nuclei. Their simultaneous determination may provide improved understanding of atmospheric processes. We developed a new analytical method allowing for a single step determination of majority of carboxylic acids and aldehydes (+95 compounds). This sample preparation employed O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA·HCl) in methanol to yield oximes (for aldehydes) and methyl esters (for majority of acids); with the limits of detection of 0.02-1 ng per injection, corresponding to approximately 0.4-20 μg/g. Subsequent trimethylsilylation with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) was employed only for aromatic acids, which were not completely esterified, and for hydroxyl groups. Our method, in contrast to previous primarily qualitative studies, based on derivatization with an aqueous PFBHA followed by BSTFA derivatization, is less labor-intesive and reduces sample losses caused by an evaporation. The method was tested with a broad range of functionalized compounds (95), including monocarboxylic, dicarboxylic and aromatic acids, ketoacids, hydroxyacids and aldehydes. The developed protocol was applied to wood smoke (WS) and urban air standard reference material 1648b (UA) PM. The observed concentrations of aldehydes were 10-3000 μg/g in WS PM and 10-900 μg/g in UA PM, while those of acids were 20-1800 μg/g in WS PM and 15-1200 μg/g in UA PM. The most prominent aldehydes were syringaldehyde and vanillin in WS PM and glyoxal in UA PM. The most abundant acids in both PM samples were short-chain dicarboxylic acids (≤C). WS PM had a high abundance of hydroxyacids (vanillic and malic acids) as well as ketoacids (glutaric and oxalacetic) while UA PM also featured a high abundance of long-chain monocarboxylic acids (≥C).