Abstract
The oxidation of pyridoxal 2-pyridylhydrazone by hydrogen peroxide is induced by Fe(II). The reaction is monitored fluorimetrically and is preceded by an induction period, the length of which is inversely proportional to the Fe(II) concentration. This effect allows the quantitative determination of this ion. The traditional kinetic methods (tangent, fixed time, and variable time) have also been applied and between 5 and 60 ng/mL of Fe(II) can be determined. The transient inhibitory effect of Cr(VI) on the first stage of this oxidation is reported. A noncatalytic cycle appears to be associated with them. The conversion of the rate-modifying ion to an inactive form by a redox reaction seems to account for the lack of a catalytic cycle. A judicious choice of reaction conditions permits the determination of 50-1000 ng/mL of Cr(VI). The determination of the Fe(II)-Cr(VI) mixture (10-70 ng/mL Fe(II) and 50-350 ng/mL Cr(VI)) is reported on the basis of this transient inhibitory effect through initial rate and length of induction period measurements. 22 references, 3 figures, 3 tables.
Published Version
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