Simple and rapid determination of iodide in table salt by stripping potentiometry at a carbon-paste electrode

Abstract.

A simple and rapid procedure, utilising constant-current stripping analysis (CCSA) at a carbon-paste electrode containing tricresyl phosphate as a pasting liquid (TCP-CPE), has been developed for the determination of iodide in table salt. Because of a synergistic accumulation mechanism based on ion-pairing and extraction of iodide in combination with electrolytic pretreatment of the TCP-CPE, the method is selective for iodide and enables direct determination of iodide in samples of table salt containing anticaking agents such as K₄[Fe(CN)₆] (food additive "E 536") or MgO. The iodide content (calculated as KI) can be determined in a concentration range of 2 to 100 mg kg^–1 salt, with a detection limit (S/N=3) of 1 mg kg^–1, and a recovery from 90 to 115%. The proposed method has been used to determine iodide in several types of artificially iodised table salt and in one sample of natural sea salt. The results obtained agreed well with those obtained by use of three independent reference methods (titration, spectrophotometry, and ICP–MS) used to validate the CCSA method, indicating that the developed method is applicable as a routine procedure for rapid testing in salt production process control and in the analysis of marketed table salts.