Interlaboratory evaluation of an off-line supercritical fluid extraction and gas chromatography with atomic emission detection method for the determination of organotin compounds in soil and sediments

Abstract

A collaborative study was conducted, with eight laboratories participating, to determine the method accuracy and precision of an off-line supercritical fluid extraction (SFE) method for organotin compounds. This method involves extraction of organotin compounds from solid matrixes with supercritical carbon dioxide, modified with 5% methanol, at 450 atm and 60°C for 20 min in the static mode followed by 30 min in the dynamic mode. The extracted material was collected in either methylene chloride or on a C 18-bonded silica trap followed by a methylene chloride rinse. The extracted material was derivatized with pentyl magnesium bromide and analyzed by gas chromatography with atomic emission detection (GC-AED). The study design was based on the AOAC blind-replicate design with balanced replicates. The study samples consisted of three solid matrixes that were spiked with organotin compounds at 1000 ng/g (as Sn) and one unspiked matrix that contained dibutyltin and tributyltin compounds at independently determined levels. The results of this interlaboratory study indicate that the SFE method works satisfactorily for the tri- and tetra-substituted organotin compounds but that the di-and mono-substituted organotin compounds are quite difficult to extract under these conditions. Higher pressures and different modifiers may be required to enable extraction of the mono- and di-substituted organotin compounds from soils and sediments.