A flow system for the spectrophotometric determination of lead in different types of waters using ion-exchange for pre-concentration and elimination of interferences

摘要

A flow system for the spectrophotometric determination of lead in natural and waste waters is proposed. The determination is based on thecolorimetric reaction between malachite green and iodide, followed by the formation of a ternary complex between those reagents and leadcations. The developed flow system includes a lead pre-concentration step in a column packed with a cationic resin (Chelex 100) operatingin a sequential injection mode. To improve the mixture of sample and reagents, a flow injection approach was adopted for the colorimetricdetermination. This way a hybrid flow system, involving both sequential and flow injection concepts was designed. Another feature of theproposed system is the efficient elimination of major interferent species, such as cadmium and copper. The elimination of cadmium interferenceis obtained by complexing Cd2+ with chloride and retaining the formed negatively charged complexes in an anionic resin, AG1 X-8. As forcopper, with the presence of both ionic resins as well as the conditions for cadmium elimination, it no longer acts as an interferent. Differentranges of lead concentration (50–300 and 300–1000 g l−1) can be determined with minor changes in the controlling software, useful forapplication to both natural and waste waters. Therefore, a detection limit of 25 g l−1 was achieved. Repeatability was evaluated from 10consecutive determinations being the results better than 4%. The recoveries of lead spikes added to the samples ranged from 93 to 102%. Thesampling frequency was 17 and 24 determinations per hour, for 50–300 and 300–1000 g l−1 ranges, respectively.