Highly sensitive voltammetric sensor for iodide determination based on carbon paste electrode modified with nanosized sulfate-modified α-𝐅𝐞𝟐𝐎𝟑

Iodide is an essential micronutrient for human body organism. It plays an important role in mental development, growth and basic metabolis 1, 2 and its deficiency in the body is a serious threat because it is associated with thyroid and neurological disorders 3. Recommended daily allowance (RDA) of iodine for adults is 140–200 μg/d 4. On the other hand, deficiency and excess amount of iodine both can produce thyroid disorder, and further reduce various disease and hypothyroidism as well as hyperthyroidism 5, 6. Iodide is present in waters 7, food 8, pharmaceutical preparations 4, clinical 9, fodder 10, biological samples 11 and environmental samples 12. Iodine species belongs to the toxic elements and causes pollution in the environment, especially because one of its radioactive isotopes, which have harmful impact13. Therefore, in the context of radioactive waste management and biological role of iodine, a number of analytical methods are employed and have been suggested to evaluate iodine speciation in the natural environment 14, 15. At present, several analytical methods have been proposed for the determination of iodide including, UV–vis spectrophotometry 16-19, spectrophotometric 20, chemiluminescence 21, flow injection 22, inductively coupled plasma (ICP-MS) 23, inductively coupled plasma–atomic emission spectrometry (ICP–AES) 24, diffuse reflectance spectroscopy 25, capillary electrophoresis 26, ion chromatography 27, gas chromatography with mass spectrometry detection 15, 28, 29 and neutron activation analysis (NAA) 30. However, most of these techniques are complex sample preparation process, expensive for routine analysis and time consuming. By comparison, electrochemical method is less expensive and has additional advantages of fast response speed, simple operation, timesaving, high sensitivity, and real-time detection in suitable condition as an analytical technique so have been successfully applied in the determination of trace iodine. 13th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 22- 23 Nov, 2017 41 Recently, much attention has been directed toward nanoparticle based sensors, in this approach we describe a new concept for simple and rapid determination of iodide. The nanosized α-Fe2O3 particles were synthesized via sol-gel technique and then modified with sulfate groups. The synthesized nanoparticles were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) methods. The obtained material was incorporated with carbon paste electrode to fabricate an iodide sensor. It was shown that the modification of hematite nanoparticles with sulfate improved the sensor efficiency. The detection process was characterized by studying the redox behavior of iodide ions at both carbon paste and modified carbon paste electrodes by cyclic voltammetry (CV), impedance and tafel curve. The effect of electrode composition (sulfated α-Fe2O3, carbon, binder, pH, scan rate and accumulation time) on its response was also investigated. The voltammetric method showed a good linear correlation coefficient (r = 0.9979) with a Nernstian behavior in a concentration range of 1.49×10-7 to 10-3 mol L-1 and a detection limit of 0.149 μmol L-1 (S/N=3) for an accumulation time of 15 min. The relative standard deviation (R.S.D.) below 3.5% for all iodide standard solutions investigated. Determination of iodine in complex real samples such as sea water and soil were performed with high accuracy and satisfactory recovery results. The results were compared to those obtained by reference methods. The effect of different cations and anions interference was also discussed. The presence of sulfated α-Fe2O3in electrode composition was found to considerably facilitate iodide oxidation, with response currents directly related to iodide concentration.