Thermospray ionization liquid chromatography-mass spectrometry and chemical ionization gas chromatography-mass spectrometry of hexazinone metabolites in soil and vegetation extracts

Abstract

We have used thermospray LC-MS to confirm three highly polar metabolites (A, B, and G) of the herbicide hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione], and chemical ionization GC-MS to confirm two other metabolites (D and E) in extracts of soil and vegetation from a forest in the Central Alabama Piedmont. Selected-ion monitoring (SIM) of the protonated molecular ions of metabolite A [3-(4-hydroxycyclohexyl)-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] at mass-to-charge ratio ( m/ z) 269 and metabolite B [3-cyclohexyl-6-(methylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] at m/ z 239 gave matrix detection limits (MDLs) of 25 ppb (ng/g) and 50 ppb, respectively, in 10 g vegetation samples. MS quantitation for A and B generally confirmed high-performance liquid chromatography data. SIM of the protonated molecular ion of metabolite G [3-cyclohexyl-6-(methylamino)-1,3,5-triazine-2,4(1H,3H)-dione] at m/ z 225 afforded an MDL of 5 ppb in 50 g topsoil samples. Metabolite G was not confirmed above the MDL in any of the soils tested. Chemical ionization GC-MS using methane reagent gas gave strong ion signals for metabolite D [3-cyclohexyl-1-methyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione] at m/ z 226 and 144 and metabolite E [3-(4-hydroxycyclohexyl)-1-methyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione] at m/ z 242, 224, and 144. SIM at these masses afforded MDLs of 50 ppb for D and 400 ppb for E in 10 g vegetation samples.