Studies On The Electrochemical Determination Of Trace Pb²⁺ And Cd²⁺ Based On The Inducing Adsorption Ability Of I^-

In this work, sensitive and simple electrochemical methods were respectively developed for the determination of Pb2+and Cd2+ based on the excellent properties of acetylene black (excellent electric conductivity, large surface area and strong adsorptive ability) as well as the strong inducing adsorption abilities of I- to Pb2+ and Cd2+. The main researches were summarized as follows:In the presence of pasting liquid, an acetylene black (AB) paste electrode was prepared by homogeneously mixing 100.0 mg AB and 100.0μL paraffin oil. The anodic stripping voltammetric behaviors of Pb2+ were detailedly examined at AB paste electrode in the presence of different concentrations of I-. It was found that the stripping peak current of Pb2+ greatly increased in the presence of low concentration of I-, suggesting that I- exhibits strong inducing adsorption ability to Pb2+. Besides, the anodic stripping voltammetric responses of Pb2+ were compared at AB paste electrode and graphite paste electrode. The anodic stripping behavior of Pb2+ obviously increases at AB paste electrode, owing to the larger surface area and more active sites. In HClO4 solution containing 7.0×10?3 mol/L, Pb2+ was firstly induced to accumulate at AB paste electrode surface, and synchronously reduced to Pb under -0.90 V. During the following potential sweep from -0.90 V to -0.30 V, the reduced Pb was oxidized, resulting in a sensitive and well-shaped stripping peak at -0.56 V, which can be used as analytical signal for Pb2+. The linear range of this novel method is found to be from 2.0×10-8 to 4.0×10-6 mol/L, and the lowest detectable concentration is estimated to be 6.0×10-9 mol/L after 2-min accumulation. When the accumulation time extends to 10 min, the lowest detectable concentration is 1.0×10-9 mol/L. Finally, this newly-proposed method was used to detect Pb2+ in water samples, and the results were in good agreement with those obtained by graphite furnace atomic absorption spectrometry.The electrochemical behaviors of Cd2+ at AB paste electrode and in the presence of I- were systemically investigated, suggesting that I- also possesses obvious inducing adsorption ability to Cd2+. Based on this, a sensitive and simple electrochemical method was proposed for the determination of trace levels of Cd2+ after optimizing all the parameters. The linear range of this method is in range form 8.0×10?8 to 1.0×10?6 mol/L, and the detection limit is closely related to the accumulation time. When the accumulation time is 2 min and 4 min, the corresponding limit of detection was 2.0×10?8 mol/L and 5.0×10-9 mol/L, respectively. Finally, this method was successfully used to detect Cd2+ in water samples, and the results were consistent with those obtained by graphite furnace atomic absorption spectrometry.