Determination of butyltin compounds in coastal sea-water samples using isotope dilution GC-ICP-MS

A rapid, accurate, sensitive and simple method for the simultaneous determination of mono-, di- and tributyltin (MBT, DBT and TBT, respectively) in coastal sea-water samples was developed. The method is based on the application of isotope dilution methodologies using a Sn-119 enriched spike containing all three butyltin compounds. Sample volumes of 100 ml were introduced in pre-cleaned glass volumetric flasks and spiked with the mixed enriched spike. After 15 min equilibration, sodium tetraethylborate, acetate buffer of pH 5.4 and 1 ml of hexane were added and the mixture shaken for 10 min. The hexane phase was recovered, evaporated to near dryness under argon, and finally 1 ml was injected in the GC-ICP-MS system. Detection was performed at masses 118, 119 and 120. The concentration of the butyltin compounds in the samples was calculated based on the average value from both the 118/119 ratio and the 120/119 ratio. In this way mass bias was compensated without resorting to external mass bias correction. Instrumental detection limits were ca. 50 fg for all butyltin species (as Sn) while method detection limits were blank limited and resulted to be 0.27, 0.09 and 0.04 ng l(-1) (as Sn) for TBT, DBT and MBT, respectively. Recovery experiments both at 10 and 70 ng l 2 1 levels for TBT were quantitative and precision was about 5% RSD at levels between 2 and 20 ng l(-1) for all three butyltin compounds. The method was applied to investigate the levels of butyltin compounds in coastal sea-water from Gijon (Asturias, Spain) where no previous data existed.