Abstract

The determination of dibutyltin ions (DBT) in sediments was carried out by isotope dilution analysis using a ¹¹⁸Sn-enriched DBT spike synthesised in the laboratory. The different organotin compounds present in the sediments were separated by gas chromatography after aqueous ethylation using NaBEt₄ and extraction into hexane. Isotope ratios (peak area ratios at different masses) were measured by on-line ICP-MS detection of the GC-separated compounds. Optimum conditions for the measurement of isotope ratios by GC-ICP-MS are described. The total integration time should be lower than 0.2 s in order to follow accurately the chromatographic peak profile and avoid peak skew effects for different masses. Enriched DBT was prepared by reaction of ¹¹⁸Sn-enriched tin with butyl iodide in the presence of tetrabutylammonium iodide as catalyst and DMF as solvent. The concentration of the DBT spike was measured by reverse isotope dilution analysis with a natural DBT standard. In the analysis of DBT in sediments, the spike was added directly to the solid sample and extracted with a methanol–acetic acid mixture. No recovery corrections for aqueous ethylation or extraction into hexane were necessary and no rearrangement reactions (artifacts) were evident from the isotope ratios found for the different organotin compounds present in the samples. The method was applied to the determination of DBT in sediment reference materials with satisfactory results.