Optimization of GC–ICPMS system parameters for the determination of butyltin compounds in Hungarian freshwater origin sediment and mussel samples

The optimization and application of gas chromatograph coupled with inductively coupled plasma mass spectrometer (GC–ICPMS) (equipped with a commercially available interface) for the speciation of butyltin compounds in freshwater origin sediment and mussel samples is described. Optimization focused on the system parameters that have the greatest effect on signal intensity such as plasma power, ion lenses and make up gas flow (in the interface). Xenon (Xe) containing argon gas (Ar) was applied as tuning gas providing continuous Xe signal for the optimization of system parameters. It was found that plasma power and make up gas are interrelated variables and provide a set of paired optimum values at each power settings. The absolute optimum values obtained at 800 W plasma power and 1.2 L min−1 make up gas flow rate when 7 mm sample depth was adjusted. The optimum settings obtained were then checked by means of a test solution (tetraethyltin dissolved in hexane). Same optimum conditions were found when tin (Sn) transient signals were monitored. Detection limits were calculated for the three species using the optimized system parameters. Detection limits are the following: for monobutyltin (MBT) 5.6 ng Sn kg−1, for dibutyltin (DBT) 6.6 ng Sn kg−1 and for tributyltin (TBT) 3.4 ng Sn kg−1 obtained. Determination of the butyltin compounds were carried out by means of species-specific isotope dilution analysis. The spike solution contained all species investigated but with altered isotopic composition. Each species were enriched in their 119Sn isotope. Concentrations found in Hungarian freshwater origin mussel and sediment samples ranged between 19 and 39 ng g−1for MBT, between 1.2 and 6.3 ng g−1 for DBT and between 1.2 and 3.2 ng g−1 for TBT indicated as Sn in dry weight. Validation of the method was done by means of certified reference materials (BCR CRM 646 and 477). Good agreement was found between certified and experimental values. Normalized deviation (En) was also computed in order to validate the method used. En values obtained ranged between 0.07 and 0.11 for mussel samples and between 0.26 and 0.72 for sediment samples. These values show that isotope dilution–GC–ICPMS methodology is valid for the determination of MBT, DBT and TBT from both types of matrices.