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 i n situ ethylation, simultaneous solid-phase microextraction of the derivati ves, followed by a gas chromatographic analysis with flame photometric dete ction. Experimental design methodology was used to evaluate the influence o f 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 param eter and two other factors are positively significant: the adsorption time and the sample volume. The adsorption profiles and the optimal operating co nditions 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 linea rity 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 th e accuracy of the optimized method by comparing results with those obtained using a conventional solvent extraction of the ethylated organotins. (C) 1 998 Elsevier Science B.V. All rights reserved.