Jerry L. Michael

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.

Determination of picloram in soil and water by reversed-phase liquid chromatography

A reversed-phase liquid Chromatographic method is presented for the determination of picloram in the parts per billion 2 (ppb) range in soil, soil solution, and stream samples. Quantification is effected by UV absorption at 254 nm. Derivatization is not necessary. The method permits 92% ±7.1 recovery from water samples and 61.8% ± 11.1 recovery from soil samples.

Evaluation of Water Sampling and Storage Procedures Used in Herbicide Dissipation Studies

The recoveries of six herbicides (triclopyr, triclopyr ester, sulfometuron methyl, metsulfuron methyl, imazapyr, and hexazinone) from stream water samples containing two levels of dissolved organic matter were evaluated. Simulated field study conditions were used to evaluate collection, ambient (pre-retrieval) field storage, and freezer storage phases of stream water sampling. Herbicide residue levels were determined by reversed-phase high performance liquid chromatography with ultraviolet absorbance detection. Method detection levels and stability curves were developed for each herbicide in each water matrix. None of the herbicides degraded significantly in either stream water at up to 24 days of dark storage at 22-25oC except for sulfometuron methyl, which declined 9-16% after 24 days in both samples. Triclopyr, triclopyr ester, metsulfuron methyl, imazapyr, and hexazinone did not degrade significantly in either stream water after 12 months’ storage below -15oC. Sulfometuron methyl recovery declined 15-20% after 12 months in both stream water samples. None of the herbicides tested appeared to leach from the automatic sampler tubing into subsequently-collected samples. However slight carryover of about 1.0% of the spiking level was observed in the first post-spike blanks collected for all herbicides due to physical adhesion of residual water droplets on the tubing walls. No detectable carryover was observed in the second or third post-spike blanks for any of the herbicide-stream water combinations tested.