DETERMINATION OF CHLORIDE BY FLOW-INJECTION SPECTROPHOTOMETRY WITH MEMBRANE REAGENT INTRODUCTION

A single line manifold incorporating three Nafion(R) membrane reactors has been developed for the sequential introduction of components of t he mercuric thiocyanate/iron(III)/acid reagent for the determination o f chloride. Nitric acid was introduced at the first reactor to give su fficient ionic strength to allow cation exchange of FeSCN2+ at the sec ond reactor, and Hg2+ at the third reactor. The composition of the rea gent was adjusted by control of the flow rates of donor and acceptor s treams, reagent concentration and reactor length. Calibration over the range 0.3-25 mu g ml(-1) was possible, though the calibration functio n was curved. The manifold was used to determine chloride in river wat er and in pond water at concentrations of 8 and 47 mu g ml respectivel y and gave results that were not significantly different from those ob tained by an EPA method. The lower range sensitivity was 0.032 absorba nce mu g ml(-1), which compares favorably with that of other flow inje ction methods, but the detection limit was 300 ng ml(-1), considerably higher than that can be achieved by Bow injection procedures. This wa s due to the presence of mixing noise caused by fluctuations in reagen t concentration related to pulsations in the how in both donor and acc eptor streams. Valve switching and refractive index effects were absen t. (C) 1998 Elsevier Science B.V.