Stir bar sorptive 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 preconcentration capabilities of a new extraction techni que, 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 determina tion of the organotin compounds tributyltin (TBuT) and triphenyltin (TPhT) in aqueous standard solutions, harbor water, and mussels (after digestion w ith tetramethylammonium hydroxide). Throughout, tripropyltin for TBuT and t ricyclohexyltin for TPhT were used as internal standards to correct for var iations in the derivatization and extraction efficiency, Calibration was ac complished by means of single standard addition. Derivatization to transfor m the trisubstituted compounds into sufficiently volatile compounds was car ried out with sodium tetraethylborate, The compounds were extracted from th eir aqueous matrix using a stir bar of 1-cm length, coated with 55 muL of p oly(dimethylsiloxane) (PDMS), After 15 min of extraction, the stir bar was desorbed in a thermal desorption unit at 290 degreesC for 15 min, during wh ich the compounds were cold-trapped on a precolumn at -40 degreesC. Flash h eating 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 d egreesC) transfer line. Monitoring of the Sn-120(+) 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) (d ry weight) TPhT was found. The accuracy of the method was checked by the de termination 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.