Determination of medium- and long-chain perfluorocarboxylic acids in water by catalytic methylation with trimethylsilyl diazomethane and gas chromatography - Mass spectrometry analysis

Perfluorocarboxylic acids (PFCAs) have received wide public concern, due to their biotoxicity and universality. However, the current LC-MS method suffers from the background interference originating from the instrumental system and the time-consuming procedure in analyzing long-chain PFCAs. In this work, we established a rapid method for the determination of medium- and long-chain PFCAs based on derivatization with trimethylsilyl diazomethane (TMSD) and GC-MS analysis. Under the catalysis of trimethylchlorosilane, methylation of trace PFCAs with TMSD was fully achieved within only 2 min, which represents inaugural efficient methylation of carboxylic acid. The methylated products of 9 PFCAs (C7–C18 except C15 and C17) were determined by GC-MS/MS within a GC run of 13 min. Moreover, this method successfully avoided the background interference in the HPLC-MS analysis, which made analytical results more reliable. The quantitative linear range was 0.1–100 ng/mL for medium PFCAs (C8 to C13), 1–1000 ng/mL for C7 and long-chain PFCAs (C14 to C18), respectively. Good reproducibility was obtained for all PFCAs, with an intra-day RSD of 0.90–4.35 % and an inter-day RSD of 2.62–5.64 % at 5 ng/mL. The recovery rate was 83.2–111.3 % at 10 ng/mL, indicating the accuracy and reliability of these results. These results indicated that this method provided a practical and reliable method for the detection of medium- and long-chain perfluorocarboxylic acids in water samples by GC-MS analysis.