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

A collaborative study was Conducted, with eight laboratories participa ting, to determine the method accuracy and precision of an off-line su percritical fluid extraction (SFE) method for organotin compounds. Thi s method involves extraction of organotin compounds from solid matrixe s with supercritical carbon dioxide, modified with 5% methanol, at 450 atm and 60 degrees C for 20 min in the static mode followed by 30 min in the dynamic mode. The extracted material was collected in either m ethylene chloride or on a C-18-bonded silica trap followed by a methyl ene chloride rinse. The extracted material was derivatized with pentyl magnesium bromide and analyzed by gas chromatography with atomic emis sion 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 an d tributyltin compounds at independently determined levels. The result s of this interlaboratory study indicate that the SFE method works sat isfactorily for the tri- and tetra-substituted organotin compounds but that the di- and mono-substituted organotin compounds are quite diffi cult to extract under these conditions. Higher pressures and different modifiers may be required to enable extraction of the mono- and di-su bstituted organotin compounds from soils and sediments. (C) 1997 Elsev ier Science B.V.