Optimization of solid-phase microextraction for the speciation of butyl- and phenyltins using experimental designs

This paper deals with the optimization of solid-phase microextraction (SPME) for organotin speciation in water. The analytical method consists of an in situ ethylation, simultaneous solid-phase microextraction of the derivatives, followed by a gas chromatographic analysis with flame photometric detection. Experimental design methodology was used to evaluate the influence of six analytical parameters on the mean peak area (S(mean)). The adsorption of the compounds on the SPME fibre was found to be the most important parameter and two other factors are positively significant: the adsorption time and the sample volume. The adsorption profiles and the optimal operating conditions were determined from the modelling of S(mean). The detection limits range from 2 to 4 ng l(-1) (monophenyltin excepted: 18 ng l(-1)) and linearity is from 50 to 600 ng l(-1). The relative standard deviations are 7-10% for five determinations. Water samples were analysed in order to verify the accuracy of the optimized method by comparing results with those obtained using a conventional solvent extraction of the ethylated organotins. (C) 1998 Elsevier Science B.V. All rights reserved.