Abstract
Diquat(DQ2+) and paraquat(PQ2+) are dipyridinium herbicides, which are toxic to humans. These compounds react with an ion-association reagent, TBPEH, dissolved in 1,2-dichloroethane(DCE), to form blue ion associates: (DQ2+•(TBPE−)2) and (PQ2+•(TBPE−)2). A two-line flow system was assembled. Buffer (pH 11.0) and TBPEH/DCE solutions were delivered at 0.8 ml min−1. The associate was extracted in a 5 m extracting coil. However, when a DCE waste phase containing the ion associate and aqueous waste, including TBPE ion, were mixed with 5 ml of 3 mol dm−3 sulfuric acid and stirred, yellow TBPEH was formed in DCE again. On the other hand, DQ2+(PQ2+) ion was transferred to the acidic aqueous phase. Therefore, TBPEH was regenerated in DCE and the TBPEH/DCE solution could be reused as an ion-association reagent/extracting solvent. A recycled FIA system using regenerated TBPEH with DCE was proposed. The calibration graphs were linear over the range from 0.25×10−5 mol dm−3 to 2.0×10−5 mol dm−3. When a reused reagent/DCE was delivered, the same calibration graph was obtained for DQ2+. In the case of PQ2+, the slope of the calibration graph decreased slightly; however, the linearity was good. The method was applied to the determination of DQ2+ or PQ2+ in herbicides and artificial samples. The proposed FIA is a novel and excellent method with no consumption of reagent or organic solvent.
