Expanded clay: A green and sustainable adsorbent in disposable pipette extraction (DPX) for the trace determination of cadmium ions

According to the World Health Organization (WHO), cadmium ions can lead to carcinogenic effects even at sub-ppb levels, which require sensitive analytical methods. In this work, a novel analytical method is proposed for the determination of cadmium ions at trace levels. The method consists a pre-concentration step using Disposable Pipette Extraction (DPX) and employs expanded clay as a new adsorbent material, along with flame atomic absorption detection. Kinetic models combined with adsorption isotherm studies revealed that the predominant mechanism involves the formation of chemical bonds between cadmium ions and the adsorbent. Using the optimized DPX parameters (extraction: volume of 4 mL, pH 7.5, 10 g of finely crushed expanded clay, and 5 extraction cycles; elution: 500 μL of 0.15 mol L-1 HNO as the eluent, elution time of 30 s, and 1 elution cycle), good analytical features were obtained, including a high enrichment factor value (32), a low limit of detection (0.185 μg L-1), and good precision (relative standard deviation of 3.1%; n=3). The method was applied to determine Cd2+ in water supply samples, and good accuracy was achieved (with recovery values close to 100%). Moreover, the use of expanded clay as an adsorbent in DPX procedures is attractive since is a chemically stable material and has great potential for pre-concentrating cadmium ions in aqueous media.