Physico-chemical approach to study organotin sorption-desorption during solid-phase microextraction

Solid-phase microextraction (SPME) has become a real alternative to liquid-liquid extraction in the field of speciation of organometallic compounds. Despite the high performance of this preconcentration technique, matrix effects in natural samples can affect the analytical precision. In order to understand the origin of these disturbances and control the extraction step as best as possible, the sorption-desorption behaviour of organotins was studied. In the first part, this paper discusses the analytical problems encountered in the daily use of SPME due to the particular problems observed for phenyltins. The sorption profile of these compounds was modelled using experimental design methodology to confirm the first-order kinetics. Desorption of the compounds was also observed after a given time and could not be attributed to competition between organotin compounds. In the same way, butyl- and phenyltins were studied in the presence of humic substances, which acted as representatives of organic matter found in natural samples. These substances drastically decrease the extraction yields, but do not affect the sorption profile of butyl- and phenyltins.