Screen-printed sensor for batch and flow injection potentiometric chromium(VI) monitoring
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A disposable screen-printed electrode was designed and evaluated for direct detection of chromium(VI) in batch and flow analysis. The carbon screen-printed electrode was modified with a graphite–epoxy composite. The optimal graphite–epoxy matrix contains 37.5% graphite powder, 12.5% diphenylcarbohydrazide, a selective compound for chromium(VI), and 50% epoxy resin. The principal analytical parameters of the potentiometric response in batch and flow analysis were optimized and calculated. The screen-printed sensor exhibits a response time of 20 ± 1 s. In flow analysis, the analytical frequency of sampling is 70 injections per hour using 0.1 M NaNO3 solution at pH 3 as the carrier, a flow rate of 2.5 mL·min−1, and an injection sample volume of 0.50 mL. The sensor shows potentiometric responses that are very selective for chromium(VI) ions and optimal detection limits in both static mode (2.1 × 10−7 M) and online analysis (9.4 × 10−7 M). The disposable potentiometric sensor was employed to determine toxicity levels of chromium(VI) in mineral, tap, and river waters by flow-injection potentiometry and batch potentiometry. Chromium(VI) determination was also carried out with successful results in leachates from municipal solid waste landfills.
KeywordsChromium(VI) Screen-printed electrode Graphite–epoxy composite Diphenylcarbohydrazide Flow-injection potentiometry Potentiometry
The authors are grateful to the Ministerio de Ciencia y Tecnología for financial support of this work (Plan Nacional I + D + I, no. CTQ2008-06338/BQU) and to the Comunidad Autónoma of Madrid for a research grant for one of the authors (R.A.S.-M.).
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