Reuse of ion-association reagent/organic solvent and extraction flow-injection analysis of Diquat and Paraquat

Diquat(DQ(2+)) and paraquat(PQ(2+)) 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: (DQ(2+) (.) (TBPE-)(2)) and (PQ(2+) (.) (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, DQ(2+) (PQ(2+)) 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 X 10(-5) mol dm(-3) to 2.0 X 10(-5) mol dm(-3). When a reused reagent/DCE was delivered, the same calibration graph was obtained for DQ(2+). In the case of PQ(2+), the slope of the calibration graph decreased slightly; however, the linearity was good. The method was applied to the determination of DQ(2+) or PQ(2+) in herbicides and artificial samples. The proposed FIA is a novel and excellent method with no consumption of reagent or organic solvent.