Trace analysis of sulfonylurea herbicides in soil samples using solid phase extraction and liquid chromatography with photodiodes detection

Abstract

Sulfonylurea herbicides are new class of herbicides that function by inhibiting the action of acetolactate synthase or acetohydroxyacid synthase, key enzymes in the biosynthesis of amino acids in plants. These herbicide class are applied at rates that are typically much lower than those used for the triazine or acetanilide herbicides that are most commonly used in agriculture. Despite the beneficial impact of sulfonylurea herbicides on agricultural productivity, concern has been raised by the public and regulatory authorities regarding the potential for their adverse impact on soil and environmental quality and the productivity of sensitive crop in the following season. The presence of sulfonylurea pesticide residues in soils and the low dosage used requires the application of highly sensitive analytical techniques to detect trace concentrations of residues in soil. The method has been developed for confirmation and quantitation of three sulfonylurea herbicides including oxasulfuron, triasulfuron and prosulfuron in soil samples by high performance liquid chromatography (HPLC) with photodiodes detection and chromatograms were extracted at 230 nm. Reverse phase liquid chromatography was used for the separation, identification and quantification of these compounds. Analytes were extracted from the soil samples with methanol-phosphate buffer (2:8, v/v) (pH 8) in an ultrasonic bath. The extracts were adjusted to pH 6.5 with 0.5% CH3COOH and passed, under vacuum, through a solid-phase extraction cartridge. The procedure involves a preconcentration step based on solid-phase extraction with silica-based bonded C18 cartridge and a N-vinyl-pyrrolidone polymer cartridge (Oasis HLB). The best results were obtained with Oasis HLB using 0.1% CH3COOH in acetonitrile as elution solvent. Spiked soil at 0.01-1.0 mg/kg levels was checked, Average recoveries of analytes from soil samples was in the range of 85-109% with a relative standard deviation of <4.2%. The limit of detection (LOD) of this method was in the range of 0.4 to 3.5 yg/kg. The proposed method is fast, easy to perform and could be utilized for monitoring of of three sulfonylurea herbicides including oxasulfuron, triasulfuron and prosulfuron residues in soil samples.