A microcolumn method for hexazinone and metabolite residues in soil and vegetation

Abstract

A soil cleanup method using a disposable microcolumn and a modified capillary gas chromatographic method is described for the analysis of hexazinone (3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione) and two primary metabolites, 3-(4-hydroxycyclohexyl)-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione (metabolite A) and 3-cyclohexyl-6-(methylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione (metabolite B). The limits of detection (LOD) were 7, 18, and 36 ng g−1 for hexazinone, metabolite B, and metabolite A, respectively; limits of quantitation (LOQ) were 22, 52, and 99 ng g−1, respectively. The mean recoveries were 94 ± 3% and 94 ± 5% for hexazinone and the phytotoxic metabolite B fortified above LOQ and ranging from 0.03 to 6.25 and 0.06 to 12.5 μg g−1, respectively. The recoveries from the non-phytotoxic metabolite A above LOQ increased with concentrations from 0.125 to 25 μg g−1, but were consistent at each level. The final product of cleanup was stable for at least 6 months, and no derivatization was needed before gas chromatography. The use of toluene as the final solvent and the modification of the injection system of the gas chromatograph improved the stability of peak responses. The method is three times more efficient than conventional methods. The cleanup method for soils was modified for the analysis of vegetation samples. Efficient removal of chlorophyll enabled quantitation of hexazinone by gas chromatography. Recoveries of hexazinone ranged from 73 to 96% for forest litter and four different plant species.