Speciation analysis for organotin compounds in sediments by capillary gas chromatography with flame photometric detection after microwave-assisted acid leaching
Résumé
A rapid method is described for the speciation of butyl-and phenyltin compounds in sediments. The procedure was based on the quantitative microwave-assisted leaching of the target compounds from a sediment sample with ethanoic acid followed by their derivatization with sodium tetraethylborate in the aqueous phase. The ethyl derivatives of the analyte compounds were subsequently extracted into iso-octane and separated by capillary GC. A modified flame photometer with a graphite burner fitted with a 610 nm bandpass filter was used for detection. A desulfurization procedure used prior to GC was optimized and then incorporated into the analytical scheme in order to remove the sulfur present in sediments which would otherwise interfere with the detection of the organotin compounds. The leaching of the analyte species in a focused microwave field took only 3-4 min and the analysis time was limited by the duration of the gas chromatographic run (15 min). The effects of pH, temperature and time for ethylation of methyl-, butyl-, phenyl-, octyl- and dodecyltin compounds were evaluated. The possibility of accelerating the ethylation, by using a focused microwave field, was examined. The detection limit of the procedure was 10 ng g-1 for 0.5 g of sediment. A typical precision for this determination was 5-10%. The method developed was validated by analysing two CRMs (NRCC PACS-1 and BCR CRM 462). A series of applications in the Arcachon Bay and Greek coastal monitoring programme demonstrated the presence of butyl and phenyltin species.