Design and Development of Sensors for Semi-Quantitative Analysis of Heavy Metals in Aqueous Solution

The purpose of this research was to design and develop semi-quantitative detecting sensors for heavy metals in aqueous solution. Based on the interaction of Cu²⁺, Pb²⁺, Fe³⁺ and Cr³⁺ with the adsorbed dyes or reagents such as 4-(2-Pyridylazo)resorcinol (PAR), Potassium thiocyanate (KSCN), Alizarin red S (ARS) and Dithizone (DTZ) on the TTAB-treated paper, the colors of the complexes were observed on the modified paper, depending on the types, concentrations and pH values of the dyes/reagents and the heavy metal ions. The change in color intensity was used as the standard color bands for semi-quantitative analysis of heavy metal ions by naked eye detection and optical images from smartphone detection. The types, concentration and pH solution were investigated in order to obtain the optimum condition for preparing the standard color bands. The limit of detection (LOD) was also investigated by naked eye detection. For selective detection, PAR-coated paper was used for Cu²⁺ and Fe³⁺ with LOD of 0.4 mg/L (pH 5.0). In addition, DTZ-coated paper was also selectively used for Cu²⁺ with LOD of 0.1 mg/L (pH 1.0), Cr³⁺ with LOD of 1.6 mg/L (pH 1.0) and Pb²⁺ with LOD of 0.1 mg/L (pH 5.0). For specific detection, KSCN-coated paper was used for Fe³⁺ with LOD of 0.4 mg/L (pH 1.0). In addition, ARS-coated paper was also specifically used for Pb²⁺ with LOD of 0.06 mg/L (pH 5.0). The purposed sensors were applied for semi-quantitative analysis of these heavy metal ions in drinking water samples. The detection was easy, convenient and not required sample preparation.