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Determination of selected organochlorine and organophosphate pesticides in soils using supercritical fluid extraction, solid-phase extraction, and gas chromatography with electron capture detection

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Description: The supercritical fluid extraction (SFE) of 12 selected organochlorine and organophosphate pesticides from soils using CO$\sb2$ and CO$\sb2$ modified with 3% methanol was investigated and compared to the classical sonication and Soxhlet extractions. A method was also developed and evaluated which incorporated reversed-phase solid phase extraction (SPE) with C$\sb{18}$ disks to concentrate the pesticides in methanol extracts of soils. Maximum SFE pesticide recoveries were found at higher densities ($>$0.5 g/mL). Temperature over the range of 40$\sp\circ$ to 120$\sp\circ$C had little effect on the recoveries of most of the pesticides. A static soak prior to dynamic removal also had little influence in speeding SFE rates. Pure CO$\sb2$ was unable to remove the polar pesticides from fortified soils, although recoveries greater than 80% were achieved for the nonpolar organochlorine pesticides. When CO$\sb2$ with 3% methanol was used, all of the pesticides were efficiently extracted from all of the soils (overall average recovery of 94% and overall average RSD of 5%). A small amount of moisture added to spiked top soil increased polar pesticide recoveries when pure CO$\sb2$ was used and highest overall recovery of the pesticides was realized at near neutral pH (6.4). When replicate extractions (n = 8 or 9) were performed on a fortified batch of top soil, the overall average recoveries for the sonication, soxhlet, and supercritical fluid extractions were 95%, 93%, and 92%, respectively. SFE demonstrated the best precision of the three extraction methods with the overall average RSD being 2.9%. Comparable recoveries and precisions between SFE and the sonication method were demonstrated for several real-world samples. During SPE, low recoveries of mirex and DCB (20 to 60%) were observed, because of their low solubility in the methanol/water extracts. Two of the organophosphate pesticides, dichlorvos, and methidathion were poorly retained (4 to 30%) on the C$\sb{18}$ disks. SPE recoveries (75 to 130%) of the other pesticides from a top soil and two fortified real-world soils compared well with sonication recoveries (56 to 130%) of these pesticides. Comparable recoveries of organochlorine pesticides from a contaminated native soil were also observed for sonication and SPE.
Language: English
Format: Degree Work