Isotope dilution analysis as a definitive tool for the speciation of organotin compounds.

Different spike solutions available for the determination of butyltin compounds by isotope dilution analysis are described and applied for the determination of butyltin compounds in PACS-2 certified reference material. Additionally, those spike solutions were evaluated during the course of an interlaboratory exercise organised by the National Research Council of Canada and the Laboratory of the Government Chemist (UK) in order to quantify tributyltin in a pilot sediment. The aim of this project was to evaluate the capabilities of isotope dilution mass spectrometry to reduce the uncertainty in the certification of Reference Materials for the speciation of organotin compounds. All participants were supplied with a 17Sn-enriched TBT solution from the Laboratory of the Government Chemist (UK). In our case, we performed the analysis of the pilot sediment also using a 119Sn enriched spike (mixed mono-, di- and tributyltin) and a 118Sn-119Sn double spike. The use of these additional spike solutions not only allowed the determination of monobutyltin and dibutyltin in the pilot sediment but also the evaluation and correction of possible extraction-derived rearrangement reactions. An excellent agreement amongst our results and between the participants was obtained with a precision of 8.4% RSD at a level of ca. 80 ng TBT g(-1) (as Sn).