Visualization detection of ultratrace lead and cadmium ions using cellulose acetate membrane based on silver stain

This study has developed a new membrane based visualization method for the detection of ultratrace lead and cadmium ions. The basic steps were mainly as follows. Dithizone (Dz) was adsorbed on cellulose acetate membrane (CAM) and formed Dz-Pb 2+ /Cd 2+ complexes in the presence of lead and cadmium ions. Then the complexes were converted into Dz-PbS/CdS composites after further processing with sulfide ions. While the new formed Dz-PbS/CdS composites could act as a catalyst in the subsequent silver stain reaction. With the silver nanoparticles depositing on CAM, the color of the membrane turned gray to black, which could be observed by naked eye. Semi-quantitative analysis of Pb 2+ /Cd 2+ was performed according to the ΔAverage gray value of CAM grayscale images. Results showed that under the optimal conditions, ΔAverage gray value had a good linear relation with the logarithm of the Pb 2+ /Cd 2+ concentration in the range from 1   nM to 100   nM, and the naked eye detection limit could reach 1   nM (∼0.0002   mg   L −1 ). Besides, other common metal ions had no significant interference with the detection, indicating that the method had a good selectivity. Satisfactory results were obtained for the detection of Pb 2+ /Cd 2+ in real samples (lake water and soil samples).