SPECIATION ANALYSIS OF CR-III-CR-VI USING FLOW-INJECTION ANALYSIS WITH FLUOROMETRIC DETECTION

A relatively simple, sensitive, selective, automatic fluorimetric meth od for the simultaneous determination of chromium(III) and chromium(vr ) by flow injection analysis (FIA) was developed, The method is based on the selective oxidation of the non-fluorescing reagent 2-(alpha-pyr idyl)thioquinaldinamide (PTQA), which with Cr-VI yields an intensely f luorescent product (lambda(ex) = 360 nm; lambda(em) = 300 nm), Chromiu m(III) is oxidized on-line to Cr-VI with sodium metaperiodate and the Cr-VI is subsequently treated with PTQA, Fluorescence due to the sum o f Cr-III and Cr-VI is measured and Cr-III is determined from the diffe rence in fluorescence values. The effects of various analytical parame ters, such as acidity, flow rate, sample volume, temperature, reagent concentration and interfering species, were studied. Kinetic studies u sing both the stopped-flow technique and the FIA procedure were utiliz ed in order to study and optimise the oxidation conditions for Cr-III On th, basis of its oxidation efficiency. The calibration graphs were rectilinear in the ranges 0.1-10 mu g ml(-1) for Cr-VI and 0.1-1.0 mu g ml(-1) for Cr-III, The method was successfully verified by performin g recovery experiments of Cr in several standard reference materials ( peach leaves, sediments and tea), and it was applied to the speciation analysis of Cr-III-Cr-VI in environmental waters (mineral, tap and di stilled water), a food sample (tomato juice) and synthetic mixtures. U p to 30 samples per hour can be analyzed with a relative standard devi ation of about 0.1-2%.