EXPERIMENTAL-DESIGN FOR THE STUDY OF 2 DERIVATIZATION PROCEDURES FOR SIMULTANEOUS GC ANALYSIS OF ACIDIC HERBICIDES AND WATER CHLORINATION BY-PRODUCTS

Two well known derivatization procedures, pentafluorobenzylation and B F3/methanol esterification, were compared for their applications to GC analysis of acidic water micropollutants (chloroacetic and phenoxyalk anoic acids). A two-level factorial design was used to determine the i nfluence of different parameters and their interactions on each deriva tization process. The studied parameters are the reaction time, the am ount of reagent (PFBBr) or catalyst (BF3) and the temperature. Conside ring pentafluorobenzylation, the most influential factors are the conc entration of PFBBr and the interaction 'temperature-time', which impro ve the derivatization efficiency. However, a PFBBr concentration of 25 0 mg l(-1) in the reaction medium cannot be exceeded because of the in crease in interfering by-products in GC/ECD. Moreover, chloroacetic ac id derivatives are co-eluted with these compounds. This disadvantage w as not observed in the operating conditions of GC/MS. The improved pen tafluorobenzylation procedure allows the direct determination of the d erivatives in GC/ECD without any purification step. The average detect ion limits are 1.6 and 80 mu g l(-1), respectively in GC/ECD and in GC /MS. The reproducibility is 13%. For the BF3/methanol esterification, the interactions 'BF3 concentration-temperature' and 'BF3 concentratio n-reaction time' are significant and have a negative effect on the der ivatization yield. A linear model was therefore proposed and Validated in the experimental area under study. All the compounds studied were detected in GC/MS, and the average detection limit is 2 mu g l(-1). Th e reproducibility is around 7%. Therefore, after optimization, BF3/met hanol esterification followed by GC/MS is as sensitive as pentafluorob enzylation used with GC/ECD, and more reproducible. (C) 1998 Elsevier Science B.V. All rights reserved.