Selective interaction of synthetic and natural pesticides with metal ions in micellar media: extractions using aqueous biphasic systems

Abstract

Synthetic pesticides represent a class of toxic chemical compounds which are now slowly being replaced by some natural alternatives. Here we have considered two pesticides, a synthetic one (chlorpyrifos) and another naturally obtained (eugenol) pesticide, to make a comparative study of their interaction towards metal ions (Cu2+, Co2+, Ni2+ and Zn2+). A thorough study of their extraction patterns in aqueous biphasic system (ABS) has been done. Both water and 50% (w/v) (83 mM) PEG#6000 media were taken to perform the metal-pesticide complexation study. We found a selective interaction between chlorpyrifos and copper ion in PEG media. The newly formed copper-chlorpyrifos complex gives a characteristic λmax at 322 nm in UV-Vis spectral study. The binding constant of the complex is 14.48 × 103 mol−1 (from B-H plot) and it follows the first-order reaction kinetics. To study the extraction pattern, two ABSs are considered, one is PEG#6000-sodium tartrate and another one is PEG#6000-sodium citrate. Using these two ABSs, chlorpyrifos, eugenol, copper and copper-chlorpyrifos complex were extracted at different pHs (5, 7 and 9) of the salt-rich phases. Complete extractions were observed for eugenol, chlorpyrifos and Cu-chlorpyrifos complexes from all the pH of tartrate as salt-rich phase. The micellar medium of PEG#6000 is most favourable to form Cu-chlorpyrifos complex and for extraction study. The polymer-rich phase was regenerated using ultracentrifugation, thermoseparation and ion exchange methods for reuse.