Liquid–solid extraction of tributyltin from marine samples

Abstract

An analytical method based on a liquid–solid extraction (LSE) procedure followed by gas chromatography (splitless ‘hot’ injection mode) with electron-capture detection (GC-ECD) has been developed and evaluated for tributyltin (TBT) chloride in fresh and marine waters. Splitless ‘hot’ injection GC requires the rigorous exclusion of water from the eluting solvent and the sample extract solutions. Tributyltin chloride is thermally sensitive and tends to degrade in the injection liner. This thermal degradation, possibly a debutylation reaction, is enhanced in the presence of trace amounts of water. Electron capture detection, although offering adequate sensitivity, has insufficient specificity for TBT chloride at trace level concentrations. Also, the solvent, ethyl acetate, can extract compounds from the LSE column or cartridge housings. These compounds, phthalates, cresols, adipates, etc., may interfere with the measurement and detection of the analyte. Chromatograms of extracts of LSE discs and procedural blanks have ‘clean’ backgrounds in contrast to many of the LSE columns and cartridges. Extraction discs mounted in a tandem arrangement show no breakthrough of analyte from the front to the rear disc for sample volumes which ranged from 100 to 500 ml. Liquid–solid extraction appears to meet the need for sample collection (on-site), preservation/storage (column or disc) and convenient and inexpensive sample shipment. The TBT chloride can be preserved on column(s) or disc(s) for at least 1 month. Recoveries of the tin analyte at the 0.1 ng ml–1 level range between 91 and 104%.