Sequential flow‐injection potentiometric determination of iodide and iodine in povidone iodine pharmaceuticals

A potentiometric sensor‐based flow‐injection system for determining iodide is described. The system utilizes a flow‐through sandwich cell and incorporates iron (II)‐tris bathophenanthroline iodide ion pair complex as an exchange site in a PVC matrix membrane. The sensor displays a fast response for 10⁻¹ to 10⁻⁶ M iodide ion with an anionic slope of 59.1 ± 0.3 mV/concentration decade over the pH range 1 to 11. The experimental setup offers a precise, sensitive, selective and high sample throughput technique for determining iodide and iodine over a wide range of concentration. The limit of detection is 0.5 ppm iodide in a 20 μL sample. The average recovery is 99.8%, and the mean standard deviation is 0.5%. Sequential flow‐injection determination of iodide and iodine in some pharmaceutical preparations containing povidone iodine is performed by sample injection in a sodium sulfate‐ascorbic acid stream and monitoring of the total iodide equivalent to I⁻ and I₂. This is followed by injection of a second sample in an alkaline resorcinol stream and measuring of the iodide equivalent to I⁻ and 1/2 I₂. Iodine and iodide concentrations are calculated from the consecutive signals. The method gives results in good agreement with those obtained by the United States Pharmacopeia.