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 con ducted by the U.S. Environmental Protection Agency (EPA) in Las Vegas, especially those that minimize waste solvent generation, we have deve loped and evaluated an off-line complexation/supercritical fluid extra ction (SFE) method for 13 organotin compounds. Soil or sediment sample s, amended with a complexing agent (diethylammonium diethyldithiocarba mate), 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 brom ide to convert the ionic organotin compounds into their neutral deriva tives, which are amenable to gas chromatography with atomic emission d etection (CC-ALL). The GC-AED technique presented here exhibited good linearity between 2.5 and 2500 ng/mL (as Sn), the retention time repro ducibility was better than 0.02%, and the AED response reproducibility was better than 2%. The instrument detection limits were approximatel y 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 fina l extract volume is 1.0 mt. Several variables affecting the extraction (i.e., extraction fluid composition, pressure, temperature, extractio n 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, an d the recoveries of organotin compounds increased when the pressure wa s 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 t o 30 min. Increasing the temperature from 60 to 100 degrees C did not affect recoveries; the use of the complexing agent was needed to achie ve high recoveries of the ionic organotin compounds. Monoalkyltin spec ies, however, could not be recovered even in the presence of the compl exing agent. Single-laboratory evaluation data, which were obtained fr om two SFE systems (one performing collection of the extracted materia l by sparging through a solvent and the other by deposition of the ana lytes on an octadecyl-bonded silica sorbent trap) on five soil and sed iment samples, gave recoveries of >75% on the SFE/solvent system for a ll tri- and tetrasubstituted organotin compounds and for almost half o f the disubstituted organotin compounds; some of the recoveries were l ower on the SFE/sorbent system.