Stir BarSorptive Extraction for the Determination of ppq-Level Traces of Organotin Compounds in Environmental Samples with Thermal Desorption-Capillary Gas Chromatography-ICP Mass Spectrometry

The extraction and precoacentration capabilities of a new extraction technique, stir bar sorptive extraction, were combined with the separation power of capillary gas chromatography (CGC) and the low limits of detection (LODs) of inductively coupled plasma mass spectrometry (ICPMS) for the determination of the organotin compounds tributyltin (TBuT) and triphenyltin (TPhT) in aqueous standard solutions, harbor water, and mussels (after digestion with tetramethylammonium hydroxide). Throughout, tripropyltin for TBuT and tricyclohexyltin for TPhT were used as internal standards to correct for variations in the derivatization and extraction efficiency. Calibration was accomplished by means of single standard addition. Derivatization to transform the trisubstituted compounds into sufficiently volatile compounds was carried out with sodium tetraethylborate. The compounds were extracted from their aqueous matrix using a stir bar of I-cm length, coated with 55 (mu)L poly(dimethylsiloxane) (PDMS). After 15 min of extraction, the stir bar was desorbed in a thermal desorption unit at 290 "C for 15 min, during which the compounds were cold-trapped on a precolumn at -40 °C. Flash heating was used to rapidly transfer the compounds to the GC where they were separated on a capillary column with a PDMS coating. After separation, the compounds were transported to the ICP by means of a homemade heated (270 °C) transfer line. Monitoring of the (120)Sn+ signal by ICPMS during the run of the GC provided extremely low LODs for TPhT in water: 0.1 pg L^-1 (procedure) and 10 fg L^-1 (instrumental) and a repeatability of 12% RSD (n = 10). In harbor water, concentrations of 200 pg L^-1 for TBuT and 22 pg L^-1 for TPhT were found. In fresh mussels, a concentration of 7.2 ng g-^-1 (dry weight) TPhT was found. The accuracy of the method was checked by the determination of TPhT in CRM477 (mussel tissue) and comparison of the result to that of an analysis of the same material with a classical liquid/liquid extraction with isooctane.