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.