Gold leaf electrochemical flow cell for determination of iodide in nuclear emergency tablets

This work introduces an innovative gold-leaf flow cell for electrochemical detection in flow injection (FI) analysis. The flow cell incorporates a hammered custom gold leaf electrochemical sensor. Hammered gold leaves consist of pure gold and are readily available in Thailand at affordable prices (approximately $0.085 for a sheet measuring 40 mm × 40 mm). Four sensing devices can be made from a single sheet of this gold leaf, resulting in a production cost of approximately $0.19 per sensor. Each electrochemical sensor has the gold leaf as the working electrode, together with a printed carbon strip, and a printed silver/silver chloride strip as the counter and reference electrodes, respectively. Initial investigations using cyclic voltammetry of a standard 1000 μmol L⁻¹ iodide solution in 60 mmol L⁻¹ phosphate buffer (PB) solution at pH 5, demonstrated performance comparable to that of a commercial screen-printed gold electrode. The hammered gold leaf electrode was then installed in a commercial flow cell as part of an FI system. A sample or standard iodide solution (100 μL) is injected into the first carrier stream of phosphate buffer (PB) solution, which then merges to mix with the second stream of the same buffer solution before flowing into the flow cell for amperometric detection of iodide. The optimized operating conditions include a fixed potential of +0.39 V (vs Ag/AgCl), and a total flow rate of 3 mL min⁻¹. A linear calibration is obtained in the concentration range of 1 to 1000 μmol L⁻¹ I^- with a typical equation of μA = (0.00299 ± 0.00004) × (μmol L^-1 I^-) + (0.021 ± 0.020), and R² = 0.9994. Analysis of iodide using this gold leaf-FI system is rapid with sample throughput of 86 samples h⁻¹ and %RSD of a sample of 100 μmol L⁻¹ I⁻ of 1.2 (n = 29). The limit of detection, (calculated as 2.78 × SD of regression line/slope), is 27 μmol L⁻¹ I^-. This method was successfully applied to determine iodide in nuclear emergency tablets.