Identification of the different oxidation states of iron by using a formaldehyde clock system

Abstract

In this paper, identification of iron with different oxidation states (Fe(Ⅵ), Fe(III) and Fe(II)) was firstly finalized by using a formaldehyde clock system (HCHO - NaHSO3 - Na2SO3), based on the different effects of analytes on the induction period. To put it simply, addition of K2FeO4 into the clock system made the induction period decrease while addition of FeCl3 made the induction period increase. Addition of FeCl2 had no effect on the induction period, but it reduced the slope of pH jump. Thus, these three analytes (K2FeO4, FeCl3 and FeCl2) could be identified in the concentration range of 2.0 × 10−4−1.2 × 10−3 mol L−1. Moreover, the quantitative detection of K2FeO4 and FeCl3 was realized according to the response of the induction period to the analytes concentration. The cyclic voltammetry (CV) results showed that only K2FeO4 and NaHSO3/Na2SO3 had redox reaction. The products obtained from the reactions of analytes with the clock system were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. Finally, the mechanisms of the response of the three analytes on the clock were proposed based on the experimental results.