Synthesis and adsorption studies of novel hybrid mesoporous copolymer functionalized with protoporphyrin for batch and on-line solid-phase extraction of Cd2+ ions

A hybrid copolymer [poly(ethylene glycol dimethacrylate-co-protoporphyrin)-silica], synthesized by free radical copolymerization and sol-gel process was evaluated as novel adsorbent for solid-phase extraction of Cd2+ ions. Characterization of hybrid polymer was performed by FTIR, SEM and surface area analyzes. Adsorption isotherms built at pH 8.9 were very well adjusted (R2 = 0.9982) to hybrid non-linear Langmuir-Freundlich model for two sites, indicating the existence of different affinity constants for binding sites, which was confirmed by Scatchard plot. The estimated maximum adsorption capacity was found to be 8.28 mg g−1. The adsorption kinetics data also corroborated to the isotherm, where the Cd2+ ions adsorption followed the pseudo-second-order kinetic (R2 = 0.998). The on-line preconcentration procedure, optimized by means of factorial designs, was based on sample preconcentration (16 mL) at pH 8.9 through 50.0 mg of hybrid copolymer packed in mini-column at 8.0 mL min−1 flow rate. The on-line desorption of Cd2+ ions towards the FAAS detector was carried out in countercurrent at 5.0 mL min−1 flow rate using 0.8 mol L−1 HNO3. Using the on-line preconcentration procedure, the maximum adsorption capacity determined from breakthrough curve was found to be 2.25 mg g−1. Analytical curve ranged from 0.0 up to 50.0 μg L−1 (r = 0.997), limit of detection of 0.27 μg L−1, preconcentration factor of 38.4, sample throughput of 30 h−1 and consumptive index of 0.41 mL, were achieved. The preconcentration method, very tolerable to several foreign ions, was successfully applied to the Cd2+ ions determination in water samples and cigarette sample. The accuracy was checked from analysis of certified reference materials.