Adsorptive preconcentration integrated with colorimetry for ultra-sensitive detection of lead and copper

This work proposes a novel detection method for the ultra-sensitive colorimetric determination of lead and copper in complex water matrix. The method integrates signal amplification with analytical sensing, achieved by adsorptive preconcentration and a colorimetric assay. We report for the first time a strategic application of batch adsorption as a preconcentration method and colorimetry performed directly on the adsorbent surface enriched with metal. Commercially available kaolin was used as the adsorbent to preconcentrate the metals. The colorimetric detection of Pb and Cu was achieved using sodium rhodizonate and bathocuproine salt as chromogenic indicators, respectively. This method eliminates the involvement of complex instrumentation and the need for new sensing material preparation. The proposed method possesses high sensitivity for both Pb and Cu under optimized conditions. A linear calibration curve is obtained in two concentration ranges, spanning 1 to 100 µg L^-1 with a low detection limit of 0.6 and 1.2 µg L^-1 for Pb and Cu, respectively. Further, the method enables visual detection of Pb at concentrations as low as 2.5 µg L^-1 by the naked eye. We demonstrate the practical applicability of the method by simultaneous detection of Pb and Cu in six different real-water samples with good apparent recovery % [90-120%]. Detection using hand-held devices indicates the feasibility for on-site analysis. Overall, this platform method offers a high scope for de-centralized monitoring of pollutants at concentrations which are prevailing in the environment. Integrating adsorptive preconcentration with colorimetric assay enables quantitative metal detection in environmental water sample matrix.