Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 13, 1997
Publication Date: N/A
Interpretive Summary: Metolachlor is a pesticide widely used to control weeds in corn, soybeans, and other crops. Current manual methods of metolachlor extraction from soil are labor intensive, require large amounts of hazardous solvents, and are time consuming. Developing a robotic program to automate the steps necessary for the extraction would increase output, decrease wastes and reduce human errors. The objective of this work was to program a robot to interact with new metolachlor extraction stations and to determine the efficiency of this new procedure while varying soil pH, incubation time, evaporation temperature, and perfusing evaporation gas. A computerized program was created to direct a robot to perform this extraction. The time required to perform each of the 14 steps (3.5 hrs) necessary for this procedure was manipulated to enable the robot to handle four staggered samples simultaneously thus greatly increasing the sample output. Extraction efficiency seems unaffected by soil pH (5.0 to 7.2) and duration of incubation (0 to 4 hrs) of the sample in solvent. Evaporation temperature (24, 35, and 50 deg C) and evaporation gas (nitrogen or compressed air) interacted to affect percent recovery of metolachlor. This serialized procedure increases sample output by 267% relative to the conventional extraction method, decreases hazardous waste by about 67% and reduces reagent costs by over 75%. Using the new extraction procedure, laboratory workers are enabled to process samples more rapidly using less hazardous chemicals and at much greater cost savings.
Technical Abstract: Current methods for extraction of metolachlor 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methyleethyl) acetamide) from soil are tedious and time consuming. Existing robotic stations were adapted to provide a quick and reliable automated multi-step method of metolachlor extraction from soil. The method was examined using a Barnes loam (Fine, loamy mixed Udic Haploboroll). Relative costs of extraction were also examined. Duration of incubation (0 to 4 hrs), initial soil pH (5.0 to 7.1), temperature of evaporation (24, 35, and 50 deg C), and gas used for perfusion at the evaporation station (air or nitrogen [N2]) were examined. Neither duration of incubation nor initial soil pH affected the efficiency of extraction. A complex temperature by perfusion gas interaction affected the percent recovery. At 24 deg C a small but measurable advantage in recovery, 71.1 versus 74.2%, was found when N2 was used as the perfusion gas. At 35 deg C, a clear advantage in recovery, 69.8 versus 50.5%, was obtained using compressed air. Initial incubation time in 90% methanol had no effect on percent recovery over a range of 4 hrs. At 50 deg C, perfusion gas had no effect on recovery which averaged only 38%. Relative to the conventional extraction method, the serialized robotic method increased sample output by 267%. Hazardous waste generation was decreased by about 67% and reagent cost was decreased by >75%.