Synthesis and application of isotopically labelled dibutyltin for isotope dilution analysis using gas chromatography-ICP-MS

The determination of dibutyltin ions (DBT) in sediments was carried out by isotope dilution analysis using a Sn-118-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 m asses) were measured by on-line ICP-MS detection of the GC-separated compou nds. 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 ord er to follow accurately the chromatographic peak profile and avoid peak ske w effects for different masses. Enriched DBT was prepared by reaction of Sn -118-enriched tin with butyl iodide in the presence of tetrabutylammonium i odide as catalyst and DMF as solvent. The concentration of the DBT spike wa s 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 necessar y 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 ma terials with satisfactory results.