OFF-LINE COMPLEXATION SUPERCRITICAL-FLUID EXTRACTION AND GAS-CHROMATOGRAPHY WITH ATOMIC-EMISSION DETECTION FOR THE DETERMINATION AND SPECIATION OF ORGANOTIN COMPOUNDS IN SOILS AND SEDIMENTS

As part of an ongoing evaluation of new sample preparation methods conducted by the U.S. Environmental Protection Agency (EPA) in Las Vegas, especially those that minimize waste solvent generation, we have developed and evaluated an off-line complexation/supercritical fluid extraction (SFE) method for 13 organotin compounds. Soil or sediment samples, amended with a complexing agent (diethylammonium diethyldithiocarbamate), were extracted with supercritical carbon dioxide modified with 5% methanol at 450 atm/60 degrees C, 20 min static, followed by 30 min dynamic. The extracted material was treated with pentylmagnesium bromide to convert the ionic organotin compounds into their neutral derivatives, which are amenable to gas chromatography with atomic emission detection (CC-ALL). The GC-AED technique presented here exhibited good linearity between 2.5 and 2500 ng/mL (as Sn), the retention time reproducibility was better than 0.02%, and the AED response reproducibility was better than 2%. The instrument detection limits were approximately 1 ng/mL (as Sn) per compound; this corresponds to approximately 0.2 ng of compound/g of sample when a 5-g sample is extracted and the final extract volume is 1.0 mt. Several variables affecting the extraction (i.e., extraction fluid composition, pressure, temperature, extraction time, water content, and concentration of the complexing agent) were investigated. The results indicate that carbon dioxide modified with 5% methanol is a better extraction fluid than carbon dioxide alone, and the recoveries of organotin compounds increased when the pressure was increased from 150 to 450 atm, the sample water content was reduced from 18 to 3%, and the dynamic extraction time was increased from 15 to 30 min. Increasing the temperature from 60 to 100 degrees C did not affect recoveries; the use of the complexing agent was needed to achieve high recoveries of the ionic organotin compounds. Monoalkyltin species, however, could not be recovered even in the presence of the complexing agent. Single-laboratory evaluation data, which were obtained from two SFE systems (one performing collection of the extracted material by sparging through a solvent and the other by deposition of the analytes on an octadecyl-bonded silica sorbent trap) on five soil and sediment samples, gave recoveries of >75% on the SFE/solvent system for all tri- and tetrasubstituted organotin compounds and for almost half of the disubstituted organotin compounds; some of the recoveries were lower on the SFE/sorbent system.