Highly sensitive colorimetric detection of Cd(ii) based on silica sol modified with dithizone and cationic surfactant

The cadmium ion (Cd²⁺) is highly poisonous and nondegradable and easily bioaccumulates through the food chain. Therefore, it is crucial to develop cost-effective chemical sensors for Cd²⁺ with fast response time, high selectivity, and very low detection limits. In this study, a colorimetric sensor for the determination of Cd²⁺ was fabricated by modifying silica sol with dodecyltrimethylammonium bromide (DTAB) and dithizone (DZ). Cd²⁺ formed a complex with DZ, changing the solution color immediately from purple to orange prior to detection using ultraviolet-visible spectrophotometry and a customized Cd analyzer for the precipitate. Under the optimum conditions, the developed Cd²⁺ sensor had a linear range of 0.01-0.25 mg L^-1, a low limit of detection of 5.0 μg L^-1, and outstanding repeatability. This sensor also showed good precision, with the relative standard deviations of less than 2.59% and 3.24% for the intra- and inter-day data, respectively. The proposed colorimetric method was successfully applied to determine Cd²⁺ in environmental water samples, and the results were comparable to those obtained using standard atomic absorption spectrometry. Moreover, quantitative analysis was conducted using the customized Cd analyzer to estimate the color intensity change, without requiring sophisticated scientific instruments. This colorimetric sensor can be used for the portable, cost-effective, and rapid on-site detection of Cd²⁺ in environmental water samples.