Pervaporation-flow injection with chemiluminescence detection for determination of iodide in multivitamin tablets

This paper describes the use of a pervaporation (PV) technique in a flow injection (FI) system for selective improvement in iodide analysis. Iodide in the sample zone is oxidized to iodine, which permeates through a hydrophobic membrane. Detection of the diffused iodine is achieved using the chemiluminescent (CL) emission at 425 nm that results from the reaction between iodine and luminol. The method was applied for the analysis of some pharmaceutical products, such as nuclear emergency tablets and multivitamin tablets. Ascorbic acid present in multivitamin samples interfered seriously with the analysis, and off-line sample treatment using anion exchange resin was employed to successfully remove ascorbic acid before the analysis. Ascorbic acid was flushed from the column using 0.4 M sodium nitrate followed by elution of iodide with 2 M sodium nitrate. The detection limit (3S.D.) of the system was 0.5 mg l−1, with reproducibility of 5.2% R.S.D. at 5 mg l−1. Sample throughput was determined as 30 injections h−1. There was good agreement between iodide concentrations from extracted samples determined using four different methods, i.e., PV-FI, gas diffusion-flow injection, potentiometry and ICP-MS. A comparison of the analytical features of the developed pervaporation system with these of the previously reported chemiluminescence gas diffusion-flow injection previously reported is also described.