Sensitive Flow-Injection Amperometric Detection of Iodide Using Mn3+ and As3+

Abstract

Iodide is an essential micronutrient in the human body. Therefore, it is of great interest to have a reliable analytical method for the control of its content in food and biological materials.There are numerous reports in the available literature related to the application of flow-injection methods for determination of iodide with different ways of detection. The methods include spectrophotometric iodide detections, 1 indirect flow-injection method with FAAS 2 (flame atomic apsorption spectrometry), flow-injection analysis and atomic absorption spectrometry with the on-line preconcentration, 3 chemiluminescent detection. 4 The FI (flow injection) method issued for determination of iodide ion in photograph developers using an iodide ionselective detector. 5 Iodide amounts can be estimated by FIA (flow injection analysis) methods as well, using permeable membranes. 6,7 A high selectivity was achieved by the involvement of gas-diffusion and dialysis in a FIA system. In the above-mentioned methods, the effect of interfering substances is rather low, but the LODs are higher than in direct FIA methods. Ion chromatography has been successfully applied for determination of iodide in seawater samples. 8 Also, anode or cathode stripping voltammetry were frequently employed for iodide determination after preconcentration of the samples containing either iodide or iodine and the application of a carbon-paste electrode or a chemically modified carbon-paste electrode. 9 Kinetic methods for the determination of iodide based on its catalytic effect have been widely used. [10][11][12] Pastor et al. [13][14][15] examined spectrophotometrically the kinetics of the reaction of Mn 3+ with As 3+ in the presence of sulfuric 13,14 or orthophosphoric 16 acid and iodide as a catalyst. The detection limit of 0.72 ng/L and RSD of up to 6% was achieved for iodide determination in sulfuric acid media. 13 The method was applied on determination of iodide content in some oximes that are used as antidotes for nervous gas poisoning. 14 The linear range was 1.0 × 10 -8 -8.0 × 10 -8 mol/L and for 2-[(hydroxyimino)methyl]-1-methylpyridinium iodide (2-PAM iodide) the limit of detection was 0.5 ng/mL (relative standard deviation of up to 9.1%). For iodide determination in phosphorous acid media 16 under the optimal experimental conditions in the range 0.6 -2.5 ng/mL, a relative standard deviation of up to 6.7% and a detection limit of 0.12 ng/mL was achieved.In the work of Cheng and Hibbert, 16 amperometric and potentiometric detection was applied for iodide determination on a platinum electrode at +0.9 V versus Ag/AgCl electrode. The obtained detection limit is 1.0 × 10 -6 mol/L, RSD is 2.0% for iodide concentration 1.0 × 10 -4 mol/L and the linear range is 1.0 × 10 -6 -1.0 × 10 -3 mol/L. In the system applied throughout the present study, iodide injected into the carrier flow catalyzes the reaction of Mn 3+ with As 3+, and the signal intensity, proportional to iodide concentration either in standard solution or in the sample, appears at the working...

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A Selective Iodide Ion Sensor Electrode Based on Functionalized ZnO Nanotubes

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