Improvement in measurement precision with SPME by use of isotope dilution mass spectrometry and its application to the determination of tributyltin in sediment using SPME GC-ICP-MS

A method is described for the accurate and precise determination of tributyltin (TBT) by species specific isotope dilution mass spectrometry (ID-MS) using solid phase microextraction (SPME) in combination with gas chromatographic (GC) separation and inductively coupled plasma mass spectrometric (ICP-MS) detection. Butyltin compounds were ethylated in aqueous solution with sodium tetraethylborate and the headspace sampled with a polydimethylsiloxane coated fused silica SPME fiber. The analyte was then directly transferred from the fiber to the head of the GC column for desorption following insertion of the fiber through the heated injection port. Reverse spike ID analysis was performed to determine the accurate concentration of a Sn-117-enriched TBT spike using two well characterized natural abundance TBT standards. A concentration of 0.923 +/- 0.005 mug g(-1) (one standard deviation, n = 5) as tin was obtained for TBT in National Research Council of Canada (NRCC) marine sediment PACS-2 using the present method, in good agreement with the certified value of 0.98 +/- 0.13 mug g(-1) (as 95% confidence interval). A TBT concentration of 0.93 +/- 0.09 mug g(-1) (one standard deviation, n = 5) as tin in PACS-2 was subsequently determined by standard additions calibration using tripropyltin (TPrT) as an internal standard. An eighteen-fold improvement in the precision of TBT concentration measured using ID was observed, clearly demonstrating its superiority in providing more accurate and precise results as compared to the method of standard additions. A detection limit (3s) of 0.09 ng g(-1) was estimated for TBT in PACS-2 sediment.