Simultaneous coulometric determination of iodide, bromide and chloride in a mixture by automated coupling of constant current chronopotentiometry and square wave voltammetry Original Research Article

A novel method for simultaneous coulometric titration and determination of iodide, bromide and chloride is described. An electronic circuit is used for automatic switching of three-electrode constant current chronopotentiometric operation to the three-electrode square wave voltammetric (SWV) operation using the same electrochemical device. A four-electrode cell is used in common for both methods. A pure Ag wire (99.999% purity) as the anode for chronopotentiometry, SMDE as the working electrode for the SWV method, auxiliary Pt wire, and triple junction Ag/AgCl reference electrodes are used in common for both sequential methods. Each experimental run contains two alternating steps with a total time of about 9 s. The first step is a constant current coulometric titration with a 1 s run time. After the coulometric titration is automatically switched off, and the second step consisting of SWV (about 8 s) is started up by computer. The voltammetric peak current is monitored for end point-detection of each halide titration. The proposed method can determine 7×10−8 mol of Br− and I− and also 2×10−7 mol of Cl− in a sample solution. The current efficiency of the method is estimated to be ≥99.5%. The method is applied to the analysis of halides in a sample of mineral water.