Use of pseudo-first order kinetics in flow injection for determination of trace inorganic iodine

Abstract

This work utilizes pseudo-first order kinetics for the determination of iodine at the part per billion (ppb) levels. Flow injection (FI) system was developed and optimised for conditions in which the indicator reaction between Ce(IV) and As(III) gives first order kinetics. This oxidation–reduction reaction is catalysed by iodide ion and has been used for determination of trace levels of iodide for many years. Under pseudo-first order condition, analysis can be made in two ways, either a full kinetic or a fixed-time method. System development is presented as well as the characteristic evaluation of the kinetics. The system, with a simple and interferent-free in-line reduction step, has allowed successful quantitation of iodate, which has never been reported for this kinetic method. The system was used to determine total inorganic iodine in bottled drinking water that had been supplemented with iodate ion to the level of 100 μg I l −1.