THE EFFECT OF INSTRUMENTAL PARAMETERS AND SOIL MATRIX ON THE RECOVERY OF ORGANOCHLORINE AND ORGANOPHOSPHATE PESTICIDES FROM SOILS USING SUPERCRITICAL-FLUID EXTRACTION

Supercritical carbon dioxide and carbon dioxide mixed with 3% methanol are used to extract various soils fortified with selected organophosphate and organochlorine pesticides to study the effects of supercritical fluid extraction (SFE) conditions and soil matrix variables on pesticide recoveries. Pesticide recoveries are shown to increase with increases in density and pressure. Temperature, however, is found to have little effect on the recoveries of most of the pesticides, although the thermal breakdown of endrin aldehyde at higher extraction temperatures is demonstrated. A static soak prior to dynamic removal seems to have little influence in speeding extraction rates. With the exception of a sand matrix, pure carbon dioxide alone is unable to remove the polar pesticides from the fortified soils, although acceptable recoveries are achieved for the nonpolar organochlorine pesticides. When CO2with 3% methanol is used, all of the pesticides are efficiently extracted from all of the soils and an overall average recovery of 94% is achieved. The SFE precision also improves, as demonstrated by an overall average RSD of 5% for methanol-modified CO2compared to an RSD of 23% when pure CO2is used. A small amount of moisture added to spiked top soil is found to behave like a modifier and increases polar pesticide recoveries when pure CO2is used. When pH of the top soil is varied, best overall recovery of the pesticides are realized at near neutral pH (6.4). Lower SFE recoveries of some pesticides are observed at acidic and basic conditions because of either hydrolysis or protonation of the pesticides. © Oxford University Press 1993.