Dual Sample Preconcentration for Simultaneous Quantification of Metal Ions Using Electrochemical and Colorimetric Assays

A paper-based method for heating preconcentration (PAD-HP) has been developed for the determination of Pb2+, Cd2+, Fe3+, and Ni2+. The design of our heating system was evaluated for dual quantification of ions using electrochemical and colorimetric methods simultaneously. The PAD-HP was used to detect Pb2+ and Cd2+ by anodic stripping voltammetry and to detect Fe3+ and Ni2+ by colorimetric reactions. Assay conditions were optimized by evaluating performance when changing the concentration of the colorimetric reagent, eluent volume, electrolyte concentration, and electrochemical parameters. Limits of detection (LOD) were determined to be 0.97 and 2.33 mu g L-1 for Pb2+ and Cd2+ (via voltammetry) and 0.03 and 0.04 mg L-1 for Fe3+ and Ni2+ (via colorimetric assay), respectively. The relative standard deviations for assays were in the range of 5.76 to 10.12%. We observed that the PAD-HP method significantly enhanced the signal of all metals ions (14-100-fold, depending on the metal) in comparison to paper-based devices that did not use a heating preconcentration system. This PAD-HP method was successfully applied to the determination of metals ions in samples of drinking water, tap water, pond water, and wastewater. These results suggest that our approach can provide a convenient strategy to monitor aqueous samples for heavy metals with high sensitivity and selectivity.