LAUSR

An automated flow analysis approach for the photometric determination of cadmium in water with improved sensitivity is described. The setup comprises a flow system module with the ability to perform sample circulation using a closed-loop strategy, and a LED-based photometer. The photometric method is based on the reaction of Cd(II) with 1,5-diphenylthiocarbazone (dithizone) in alkaline medium containing the surfactant Triton X-100. The combination of the closed-loop facility, which prevents sample dilution, with the beneficial effect of the long optical path length of the flow cell (200 mm), allows cadmium to be determined at μg L−1 levels without the need for a preconcentration step. The effectiveness of the proposed procedure was evaluated by analyzing water samples. The results show a linear response with concentrations ranging from 7.8 to 62.5 μg L−1 (r2 = 0.9989). The method has a limit of detection of 3.0 μg L−1, which is the guideline value established by the World Health Organization (WHO). A coefficient of variation of 1.6% (n = 10) for a 30.0 μg L−1 standard Cd(II) solution, a reagent consumption of 4 μg dithizone per determination, and a sampling rate of 43 determinations per hour were also achieved.