Comparison of GC–ICP–MS and HPLC–ICP–MS for species-specific isotope dilution analysis of tributyltin in sediment after accelerated solvent extraction

Abstract

This study describes a direct comparison of GC and HPLC hyphenated to ICP–MS determination of tributyltin (TBT) in sediment by species-specific isotope dilution analysis (SS-IDMS). The certified reference sediment PACS-2 (NRC, Canada) and a candidate reference sediment (P-18/HIPA-1) were extracted using an accelerated solvent extraction (ASE) procedure. For comparison of GC and LC methods an older bottle of PACS-2 was used, whilst a fresh bottle was taken for demonstration of the accuracy of the methods. The data obtained show good agreement between both methods for both the PACS-2 sediment (LC–ICP–IDMS 828±87 ng g⁻¹ TBT as Sn, GC–ICP–IDMS 848±39 ng g⁻¹ TBT as Sn) and the P-18/ HIPA-1 sediment (LC–ICP–IDMS 78.0±9.7 ng g⁻¹ TBT as Sn, GC–ICP–IDMS 79.2±3.8 ng g⁻¹ TBT as Sn). The analysis by GC–ICP–IDMS offers a greater signal-to-noise ratio and hence a superior detection limit of 0.03 pg TBT as Sn, in the sediment extracts compared to HPLC–ICP–IDMS (3 pg TBT as Sn). A comparison of the uncertainties associated with both methods indicates superior precision of the GC approach. This is related to the better reproducibility of the peak integration, which affects the isotope ratio measurements used for IDMS. The accuracy of the ASE method combined with HPLC–ICP–IDMS was demonstrated during the international interlaboratory comparison P-18 organised by the Comité Consultatif pour la Quantité de Matière (CCQM). The results obtained by GC–ICP–IDMS for a newly opened bottle of PACS-2 were 1087±77 ng g⁻¹ Sn for DBT and 876±51 ng g⁻¹ Sn for TBT (expanded uncertainties with a coverage factor of 2), which are in good agreement with the certified values of 1090±150 ng g⁻¹ Sn and 980±130 ng g⁻¹ Sn, respectively.