TRANSPORT EXTRACTION FOR TRACE-ELEMENT SEPARATION AND PRECONCENTRATION .2. PRECONCENTRATION OF IODINE FROM AQUEOUS-SOLUTIONS

Transport extraction based on solvent sublation has been used for a 40 0-fold preconcentration of iodide from aqueous samples into an immisci ble organic solvent. Separation efficiencies amounting up to 95% were obtained for iodide concentrations of 1-10 mg/l, independent of the vo lume of the aqueous samples in the range of 1-41. Iodide was oxidized to iodine, which was subsequently transport-extracted as an ionic asso ciate with the cationic surface-active agent N-cetylpyridinium chlorid e into 10 ml of benzene. The effect of various parameters (concentrati on of iodide, bubbling time, N2-gas flow-rate, volume of the aqueous p hase) on transport extraction was investigated. Kinetic investigations showed that the transport-extraction process essentially follows a mo dified Langmuir adsorption model, which makes it possible to calculate the mass-transfer rate constant of the process for each particular ca se.