Introduction Nonspecific phosphorus-containing amino acid-type herbicides such as D,L-homoalanine-4-yl(methyl)phosphonic acid (D,L-GLUF) have been increasingly used all over the world. D,L-GLUF is readily biotransformed to 3-methylphosphinicopropionic acid or 2-methylphosphinicoacetic acid by microorganisms in the soil. 1 Recently, biochemical studies concerning glufosinate-resistant crops have been also reported. 2,3 In those studies a racemic mixture was used. On the other hand, it was

more »

... d that the half-lives of elimination of D-and L-GLUF in a patient, who ingested the herbicide containing D,L-GLUF, are different from each other, and thus the respective enantiomers have different rates of transfer in the tissues. 4 Since the physiological properties such as a herbicidal activity are generally different between the enantiomers, a development of a precise, accurate, and simultaneous determination method is required for D-and L-GLUF. In our recent study, 5 a chiral separation method for D,L-GLUF, which is labeled with dansyl chloride, has been developed by capillary zone electrophoresis using a partially filling technique of γ-cyclodextrin as a chiral selector (γ-CD-CZE). The enantiomers of dansylated D,L-GLUF (Dns-D,L-GLUF) were completely separated with γ-CD and detected in the absence of γ-CD. The absolute determination of D-and L-GLUF was achieved based on the principle of enantiomeric isomer dilution (EID) 6 in which the determination was done by measuring only peak-area ratios of enantiomers without any calibration curves and comparison standards. Moreover, the quantitative recovery and the correction of recovery of D,L-GLUF in the dansyl derivatization procedure are not required at all. However, the detection limit of D-and L-GLUF calculated from the electropherogram reported 5 was relatively high at 12 mg/L (6.2 × 10 -5 M). Since the ambient water quality criteria of D,L-GLUF is 40 μg/L (2.0 × 10 -7 M), and the reference values for D,L-GLUF residue in crops are 0.05 -5 ppm (in Japan), a more sensitive detection method and preconcentration method has to be developed for the absolute determination of trace quantities of D,L-GLUF. Therefore, the highly sensitive detection method for D,L-GLUF is studied by introducing fluorescence detection and by combining it with a selective solid-phase extraction (SPE) and an on-capillary concentration method. Titanium oxide (titania) is an amphoteric metal oxide and serves as an anion-exchanger at an acidic region and a cation-exchanger at an alkaline region. 7,8 Titania selectively adsorbs the organic phosphates 9 and has been used for the selective SPE of phosphoruscontaining amino acid-type herbicides from blood samples under acidic conditions. 10 The SPE with titania is expected to be an effective pre-separation method for D,L-GLUF in the present work. Large-volume sample stacking (LVSS) is one of the oncapillary concentration methods in CZE. This is based on the remarkable slowdown of the electrophoretic migrations of ions at the boundary of a low-conductivity sample-matrix into a A highly sensitive and accurate determination method for trace quantities of enantiomers of glufosinate (D,L-GLUF), a phosphorus-containing amino acid-type herbicide, has been studied. The present method is based on the change in the mole ratio of the enantiomeric isomers after spiking of a known amount of an isomer (L-GLUF). The chiral separation and detection were made by γ-cyclodextrin modified capillary zone electrophoresis (γ-CD-CZE) with fluorescence detection. Solid-phase extraction of D,L-GLUF with titania was investigated as the pre-separation method to eliminate coexisting materials such as inorganic salts and organic compounds in river water. A separated D,L-GLUF was labeled with dansyl chloride and subjected to the on-capillary concentration using large-volume sample stacking (LVSS) before γ-CD-CZE. The detection limit of the present method was as low as 2.0 × 10 -9 M. The present method was successfully applied to a model sample containing 2.0 × 10 -7 M D,L-GLUF in river water. It was confirmed that trace quantities of Dand L-GLUF in environmental samples can be accurately determined without any calibration curves and comparison standards.