Paper Title
Baseline Resolution of Paraquatand Diquatby Silica-Based Column in Reversed-Phase Ion-Pair Liquid Chromatography

Abstract
Quantitation of paraquat and diquat on silica-based reversed-phase columns is usually not ideal even by using ion-pair techniques due to the unsatisfied separation of both species. In this study, parameters that influence the separation of paraquat and diquat by a conventional silica-based C-18 column such as ion-pair reagent, elution pH, trimethylamine and potassium halide additions in the eluent, and the flow rate of eluent were investigated thoroughly. Experimental results revealed that elution with an aqueous solution containing 0.01 M 1-hexanesulfonate, 0.3 M potassium bromide and 0.010 M triethylamine at pH 3.0 (adjusted by phosphoric acid) can achieve a baseline resolution of paraquat and diquat. Under these conditions, the repeatabilities of retention times were 0.123% and 0.116% RSD, of quantitative peak areas were 0.594% and 1.310% RSD for diquat and paraquat, respectively (n=3). Detection of diquat and paraquat were linear in the concentration range of 0.01 – 8.0 μg/mL, with correlation coefficient of 0.9999. The detection limits were 1.2 μg/L and 1.6 μg/L for diquat and paraquat, respectively. When using the method to analyze aqueous samples, the diquat and the paraquat were only existed in field water as 0.06 μg/mL and 0.11 μg/mL, respectively. The recovery of diquat and paraquat in field water were both above 91%, which is acceptable in environmental analysis. Keywords - Paraquat,Diquat, Separation, Resolution,Ion-Pair HPLC,Water Sample.