Removal of malathion from aqueous solution using De-Acidite FF-IP resin and determination by UPLC–MS/MS: Equilibrium, kinetics and thermodynamics studies

In the present study, De-Acidite FF-IP resin was used to remove a highly toxic and persistent organophosphorus pesticide (malathion) from the aqueous solution. Batch experiments were performed as a function of various experimental parameters such as effect of pH (2–10), contact time (10–120 min), resin dose (0.05–0.5 g), initial malathion concentration (0.5–2.5 µg mL−1) and temperature (25–65 °C). The concentration of malathion was determined using a sensitive, selective and rapid ultra-performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method. The uptake rate of malathion on De-Acidite FF-IP resin was rapid and equilibrium established within 40 min. Kinetics studies showed better applicability for pseudo-second-order model. The equilibrium data was fitted to Langmuir and Freundlich isotherm models and the isotherm constants were calculated for malathion. The values of thermodynamic parameters (ΔG0, ΔH0 and ΔS0) were computed from the Vanʹt Hoff plot of ln KC vs. 1/T which showed that the adsorption of malathion was feasible, endothermic and spontaneous. The regeneration studies were carried out which demonstrated a decrease in the recovery of malathion from 95% to 68% after five consecutive cycles. Breakthrough and exhaustive capacities of malathion were found to be 1.25 mg g−1 and 3.5 mg g−1, respectively.