Improvement of measurement precision of SPME-GC/MS determination of tributyltin using isotope dilution calibration

A unique approach was developed to improve the precision of quantification of tributyltin (TBT) in sediments by solid phase microextraction (SPME) using isotope dilution GC/MS. The precision of the analytical technique was initially evaluated using standard calibration solutions. In selective ion monitoring (SIM) mode, the relative standard deviation (RSD) obtained for TBT based on peak area response was 18% (n = 11). When an internal standard, tripropyltin (TPrT), was used, the RSD decreased to 12%. A significant improvement in the precision using SPME was noted when a Sn-117-enriched TBT spike was employed; the RSD decreased 4-fold to 3%. Detection limits of 0.2 and 20 ng(Sn) L-1 were achieved with SPME sampling and liquid-liquid extraction, respectively. Six analyses were performed for determination of TBT in PACS-2 sediment Certified Reference Material using both standard additions and isotope dilution procedures. For the latter, a Sn-117-enriched TBT spike was used. A concentration of 0.88 +/- 0.03 mug g(-1)(RSD 3.4%) obtained using standard additions was in good agreement with the certified value of 0.98 +/- 0.13 mug g(-1) as tin. Concentrations found using isotope dilution were 0.895 +/- 0.015 mug g(-1) (RSD 1.73%) as tin and 0.874 +/- 0.014 mug g(-1) (RSD 1.66%) as tin using a liquid-liquid extraction and SPME sampling, respectively. A 2-fold improvement in the precision of TBT concentration measurement using isotope dilution was clearly achieved, demonstrating its superiority in providing more accurate and precise results as compared to the method of standard additions. The isotope dilution technique eliminated the problem of poor reproducibility, which typically plagues SPME.