Analysis of acidic pesticides using in situ derivatization with alkylchloroformate and solid-phase microextraction (SPME) for GC-MS

A solid-phase microextraction (SPME) method was developed for the analysis of acidic pesticide residues in water, The method utilizes in situ derivati zation with butylchloroformate (BuCF), followed by on-line SPME extraction using a PDMS fibre, and analysis by GC-MS. Derivatives of the phenoxy acids mechlorprop (MCPP), dichlorprop (DCPP), MCPA and 2,4-D and their phenol de gradation products 4-chloro-2-methylphenol and 2,4-dichlorophenol (DCP) wer e identified. Detection limits at 0.16-2.3 mug/l were achieved. Optimizatio n of derivatization, ion strength, extraction time, SPME-fibre, desorption time and temperature are described. Standard curves in the range 0.5-10.0 m ug/l were fitted to a second-degree polynomial. Standard deviation (n = 5) was below 10% for the phenol derivatives, but 20-50% for the phenoxy acids. For method verification groundwater samples from a field experiment were s creened for content of MCPP and compared to the results from the HPLC analy sis. A good agreement was obtained with respect to identification of positi ve samples, even though concentrations measured by the SPME were lower than with HPLC. Even if the precision and accuracy do not meet the demands fora strictly quantitative analysis, the SPME method is suitable for screening, because it is cheap, it can be automated, and uses smaller amounts of pote ntial harmful solvents. Also, the method is less labour-intensive, as it re quires a minimum of sample preparation when compared to traditional analyse s. The acidic pesticides bentazon, dicamba, bromoxynil, ioxynil, dinoseb an d DNOC were included in the study but could not be analysed by the current method. (C) 2001 Elsevier Science Ltd. All rights reserved.