USE OF SUPERCRITICAL-FLUID EXTRACTION FOR PIRIMICARB DETERMINATION INSOIL

The suitability of a variety of neat supercritical fluids (carbon diox ide, nitrous oxide, and chlorodifluoromethane) and modifiers (toluene, methanol, pyridine, triethylamine, and pyrrolidine) with different ph ysical-chemical properties at two temperatures (50 and 100 degrees C) was evaluated for the extraction of incurred pirimicarb from topsoil. From the extraction efficiency obtained with the different modifiers a nd their chemical properties, the prevailing interactions between pest icide residue and the soil organic matter are proposed. The most effec tive extraction fluid was carbon dioxide modified with basic compounds (pyridine or triethylamine), which reflects the significance of acid- base interaction in the binding of pirimicarb to the matrix. Further, the developed SFE procedure using carbon dioxide (100 degrees C, 30 MP a, 20 mL) modified with triethylamine (5% cell volume) was compared wi th Soxhlet extraction (18 h) using methanol. Results indicate that the supercritical fluid extraction offers better precision, shorter analy sis time, and a reduction in the solvent usage by a factor of 10.