International Journal of Farming and Allied Sciences Available online at www.ijfas.com ©2014 IJFAS Journal-2014-3-11/1201-1205/ 30 November, 2014 ISSN 2322-4134 ©2014 IJFAS High Performance Liquid Chromatographic Determination of an Asymmetrical Triazine Herbicide from Soil Mohammad Mehdizadeh* PhD student in Weed Science, Department of Agronomy and Plant Breeding, Mohaghegh Ardabili University of Ardabil, Iran Corresponding author: Mohammad Mehdizadeh ABSTRACT: A rapid method for determining residues of the herbicide metribuzin in soil by laboratory experiment under controlled conditions is described. Field soil fortified with herbicide at concentration of 5 mg kg -1 soil, and maintained at field capacity moisture regime and kept at ambient temperature 25 ± 5°C. The soil samples were extracted with different ratio of methanol/water solution and the residue was estimated by HPLC with UV detection at 290 nm and a flow rate of 0.5 ml/ min. The detection limits were 0.05 mg/kg in soil. The results indicate 52.55% degradation of metribuzin in soil samples on 120-days of experiment. The methanol/water (4:1 v/v) was found to be most effective in metribuzin degradation recovery and enhances the recovery as compared to the other. The proposed method has been satisfactorily applied in soil samples showing recoveries ranging from 85% to 98% and represents a valuable procedure for analysis of metribuzin by high performance liquid chromatography (HPLC). Keywords: Degradation, Extraction, Metribuzin, Recovery, Retention Time, UV Detector INTRODUCTION Metribuzin [4-amino-6-(1-1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] is a selective systemic herbicide used for pre and post-emergence control of many grasses and broad-leaved weeds in soya beans, potatoes, tomatoes, sugar cane, and cereals at 0.07–1.05 kg a.i./ha (Tomlin, 2002). It is considered a mobile pesticide with estimated sorption coefficients in soil (Kd) generally well below 1.0 (Shaato, 2002). Metribuzin belongs to the group of triazinone herbicides, that highly water soluble (1.05 g.L −1 ) and adsorption in low-organic sandy soils is rather weak, sorption coefficients vary from 0.56 in a very sandy loam to 31.7 in a soil containing 60% organic matter (Henriksen, 2002). Metribuzin is moderately water soluble and interacts with some polar as well as nonpolar soil constituents. The solubility of metribuzin in methanol is several hundred times greater than in water (WSSA, 1983). In aqueous solution, metribuzin ionizes at very low pH (3 or less, pK/a) (Weber, 1980), resulting from protonation of the amine group. Hydrophilic binding at pH levels < 7 occurs due to hydrogen bonding rather than from ionization of the metribuzin molecule. Therefore, inclusion of water with a moderately nonpolar organic solvent improves the extraction efficiency of metribuzin from hydrophilic sites. This herbicide is considered to be of short to moderate persistence in soils. Metribuzin have received a great deal of attention because of its extensive use and potential for widespread contamination of ecosystems. For detecting low level of metribuzin which may persist in soil and groundwater, sensitive and accurate methods of analysis are desired. The primary criteria for choosing extraction solvent is based on several factors related to extraction efficiency and residue recovery. Various studies on metribuzin have been investigated by using the electro analytical method (Skopalova, 2001), chromatographic methods such as liquid chromatography (Erenchun, 1977; Lawrence, 1996; Papadakis and Mourkidos, 2002; Shah, 2011), gas chromatography (Beltran, 1997), micellar electro kinetic chromatography (Huertas-Peres, 2006; Martinez,