Fluorometric determination of asulam in water by using solid-phase extraction

A fluorometric determination method for asulam(methyl4-aminosulphonylcarbamate, herbicide) in environmental water samples by using solid-phase extraction(SPE) has been proposed. The method is based on the addition of EDTA to a sample solution for the elimination of interferences from metal ions and the use of ethylsilanized silica(tC2) and polystyrene gel (PS-2) combination cartridges to remove any fluorescent impurities in the matrix. Asulam in a sample solution (pH 2∼3) was hardly retained in the tC2 combined upon the PS-2, and retained in the PS-2. Asulam, which was slightly adsorbed on the tC2, was retained in the PS-2 by washing with 20 ml of water. Asulam was then eluted from the PS-2 with 2 ml of methanol. After adjusting the pH to 8∼10 and diluting to 10 ml, asulam was determined by measuring the fluorescence intensity at 343 nm with excitation at 252 nm. The calibration graph was linear over the range of 0.02 to 0.3 mg 1^-1 (r = 0.997). The average recovery of 0.25 mg 1^-1 asulam in 100 ml of distilled water was 98.9% (n =5) with a relative standard deviation of 1.16%. The proposed method has been successfully applied to some environmental water samples with recoveries of 93-96%.