Determination of low-molecular-weight dicarboxylic acids in atmospheric aerosols: comparison between silylation and esterification derivatization procedures for GC-MS analysis

This paper is focused on the determination of LMW dicarboxylic acids (C3-C10): the most widely used procedures, i.e., esterification with butyl alcohol and BF3 like catalyst and a silylation with N,O-bis-(Trimethylsilyl)trifluoroacetamide (BSTFA) and trimethylchlorosilane (TMCS), were investigated. For each method, the effect of various experimental parameters on the reaction yield has been investigated and optimized: time and temperature, or amount of reagents. The better procedure was searched for the faster one-step derivatization to determine C3-C10 dicarboxylic acids as target compounds. The advantages and drawbacks of the methods are investigated and compared in terms of precision and accuracy of the obtained results, sensitivity and detection limit of the procedure. The obtained results show that the silylation procedure is the method more compatible with application to chemical analysis in PM samples: satisfactory precision and accuracy are obtained for all the studied acids at the sub-nmol level at which the dicarboxylic acids are expected to be present in trace levels. Butyl esters of low molecular weight dicarboxylic acids are too volatile to yield evaporative losses and too unstable to be accurately quantified so that quantification was possible for the dicarboxylic acids. The precision and accuracy were investigated by comparing results obtained by the two procedures from the simultaneous analysis of dicarboxylic acids in the same PM2.5 and PM10 samples.