Development of a method for the simultaneous determination of phosphoric and amino acid group containing pesticides by gas chromatography with mass-selective detection: Optimization of the derivatization procedure using an experimental design approach

An integrated gas chromatographic–mass-selective detection method for the analysis of the phosphoric and amino acid group containing pesticides is presented. The analytes are derivatized using a single-step procedure for the simultaneous esterification and acetylation of the active groups of analytes (–OH, –COOH, –NH 2) by means of acetic acid and trimethyl orthoacetate. An experimental design approach based on the central composite design is used to investigate the dependence of the derivatization variables with the total yield of derivatization of pesticides. The variables selected for study were: the amount of reagents, the temperature and the reaction time. When considering the total pesticide derivatization yield, the amount of acetic acid, the reaction temperature and the reaction time are found to be statistically significant. The electron impact ionization mass spectra of the resulting derivatives are acquired and properly interpreted. Under the chromatographic conditions employed, acceptable peak separation is attained. When the selective ion monitoring mode is used for quantitation purposes, low detection limits in the range 0.05 to 14 μg/l are achieved. Recoveries of spiked water samples range from 96 to 103% and the mean RSD of the method do not exceed 3.5%.