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Determination of Alachlor, Atrazine, and Metribuzin in Soil by Resin Extraction

USDA-ARS, North Central Soil Conservation Research Lab., Morris, MN 56267.

^* Corresponding author.

ABSTRACT

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 °C to 2 d at 75 °C. The RE procedure has the same degree of precision as C₁₈-SPE and is inexpensive.

N.T. Basta is currently at the Dep. of Agronomy, Oklahoma State Univ., Stillwater, OK 74078.

Contribution from the North Central Soil Conservation Research Lab. USDA-ARS, Morris, MN, in cooperation with the Minnesota Agric. Exp. Stn., Univ. of Minnesota, St. Paul. Sci. J. Series 19 222.

Received for publication August 19, 1991.