Analytical Sciences

Sequential Flow Injection Determination of Chlorine Species Using a Triiodide-selective Electrode Detector

Bahruddin SAAD, Wan Tatt WAI, Abdussalam Salhin Mohd. ALI, and Muhammad Idiris SALEH

School of Chemical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia

A flow injection analysis (FIA) method for the determination of four residual chlorine species, namely combined available chlorine (CAC), free available chlorine (FAC), total available chlorine (TAC) and chlorite (ClO₂^-) was developed using a flow-through triiodide-selective electrode as a detector. An important strategy of speciation studies utilized the kinetic discrimination of reactions between the CAC and FAC with Fe²⁺, which was applied to the speciation of FAC, CAC and TAC. The speciation of available chlorine species and chlorite (an oxychlorine species) was achieved by using the same set-up, but using flow streams of different pH. The effects of the pH of the carrier stream, the flow rate and the sample volume were studied. The method exhibited linearity from 2.8 × 10^-6 to 2.8 × 10^-4 M active chlorine (expressed as OCl^-) with a detection limit of 1.4 × 10^-6 M. The selectivity of the method was studied by examining the minimum pH for the oxidation of iodide by other oxidants, and also by assessing the potentiometric selectivity coefficients. The proposed method was successfully applied to the determination of chlorine species in tap water, and disinfecting formulations where good agreement occurred between the proposed and standard methods were found.

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