Adsorption of levodopa onto Amberlite resins: equilibrium studies and D-optimal modeling based on response surface methodology

This paper investigates the removal of the antiparkinsonism drug levodopa from aqueous solutions utilizing weakly basic Amberlite resins. In the first step of experimental investigation, the adsorption equilibration time (0–24 h) was determined. After that, the effects of properties such as initial levodopa concentration in the solution (20–100 ppm), adsorbent amount (10–30 mg), pH (2–10), and temperature (25–40 °C) on the adsorption of levodopa with Amberlite IRA-67 were investigated. Adsorption isotherm, kinetic and thermodynamic parameters were also determined. In the next step of experimental research, the impact of adsorbent type was examined by employing the experimental design. This design work was carried out in Design-Expert® Software using D-optimal design based on response surface methodology (RSM). The highest adsorption capacities were achieved as 33.09 mg g −1 for Amberlite IRA-67 and 20.11 mg g −1 for Amberlite IRA-400. These results showed that Amberlite resins were effective in removing levodopa from the water.