A STUDY OF THE FACTORS THAT INFLUENCE THE INTERFERENCE OF Fe (III) IN THE COLOURIMETRIC ANALYSIS OF Cr (VI), IN POLLUTED WATERS

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Mario VILLALOBOS-PEÑALOSA
Margarita E. GUTIÉRREZ-RUIZ
Silvia CASTILLO-BLUM

Abstract

The interference of Fe(III) in the photometric determination of Cr(VI) in water using the diphenylcarbazide method was studied, and the following factors which affected it were analyzed: pH, temperature, sequence in the addition of reagents, contact time between Fe(III) and Cr(VI) before analysis, and elapsed time for colour development. The most important factor proved to be the contact time, as at least one Fe(III)-Cr(VI) species is formed, in basic, neutral or slightly acid media. This fact explains the contradictions found in literature concerning the existence and magnitude of the interference. Therefore, the separation of Fe(III) or the use of other methods to analyze Cr(VI)-polluted waters which also contain Fe(III), is recommended.

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