DETERMINATION OF ALACHLOR, ATRAZINE, AND METRIBUZIN IN SOIL BY RESIN EXTRACTION

An accurate and precise procedure for simultaneous resin extraction of alachlor (2-chloro-2',6'-diethyl-N-methoxymethylacetanilide), atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine), and metribuzin [4-amino-6-(1,1-dimethylethyl)-3(methylthio)-1,2,4-triazin-5(4H)-one] in soil extracts is described. The procedure consists of three steps: (i) equilibration of resin extractors (RE) with water extracts of soil, (ii) elution of pesticides from RE by using methanol, and (iii) determination and confirmation of pesticide by dual-column gas chromatography with thermionic specific detection. Recovery of dissolved pesticides by anion-exchange resin, cation-exchange resin, and nonpolar resin was studied. Ion-exchange resins generally adsorbed pesticides well, but showed poor desorption characteristics. The effect of solution pH and salt concentration on pesticide adsorption by a nonpolar resin was studied. Quantitative amounts of pesticide (> 95%) were adsorbed from solution by a nonpolar resin over a wide range of solution pH (2.5-10.0) and dissolved salt (0-100 mM NaCl). Pesticide adsorbed by RE ranged from 80 to 90%, and methanol desorbed 80 to 85% of adsorbed pesticides. Overall pesticide recoveries by the RE procedure were very reproducible with an average recovery of 67.7 +/- 2.0%. Results obtained by the RE procedure agreed closely with those obtained by solid-phase extraction (SPE) with octadecyl (C18) bonded porous silica. Extraction time required by the RE procedure is a function of temperature and decreases from 5 d at 22-degrees-C to 2 d at 75-degrees-C. The RE procedure has the same degree of precision as C18-SPE and is inexpensive.