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

We have used thermospray LC-MS to confirm three highly polar metabolites (A, B. and G) of the herbicide hexazinone [3-cyclohexyl-6-(dimethylamino)-l-methy~-1,3.S-triazine-2,4( lH,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)-I-methyl-1,3.5-triazine-2.4( lH.3H)-dione] at mass-to-charge ratio (m/z) 269 and metabolite B [3-cyclohexy1-6-(methylamino)-1-methyl-1,3,5-triazine-2.4( lH,3H)-dione] at m/z 239 gave matrix detection limits (MDLs) of 25 ppb (ngig) and 50 ppb. respectively, in IO 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)-l.3,S-triazine-2,4( lH,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-l-methyl1,3,5-triazine-2,4,6(1H,3H,SH)-trione] at miz 226 and 144 and metabolite E (3-(4-hydroxycyclohexyl)-l-methyl1,3,5-triazine-2,4,6(1H,3H,SH)-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,