Colorimetric methods for Fe(II) determination based on complexation of heterocyclic amines, such as phenanthroline (Phen) and ferrozine (FZ), have been widely used for analysis of iron species in solution, which is critical to discuss the mechanism of Fenton and related reaction systems. However, the reliability of both methods in the background of hydrogen peroxide has never been addressed. In this study, we demonstrate that serious Fe(II) overestimation possibly occurs for both methods in Fenton systems, particularly for the Phen method. A systematic variation of incubation conditions reveals that the available Fe(II) concentration depends greatly on the incubation time after mixing the colorimetric reagents with the sample. Also, it is highly sensitive to pH and temperature as well as the initial concentrations of Fe(III), H₂O₂, and acetate buffer. The experimental results combined with simulations indicate that Fe(II) overestimation mainly results from the reduction of Fe(III)-Phen or Fe(III)-FZ complexes by residual H₂O₂ during analysis, a reaction that is facilitated by the ligand field effect of the heterocyclic amine. An effective remedy for the instability and inaccuracy of the methods in the presence of H₂O₂ is the addition of NH₄F to the incubation mixture (55 mM for Phen and 35 mM for FZ), which converts residual Fe(III) to a colorless and reduction-insensitive fluoride complex.

基于菲咯啉（Phen）和二茂铁（FZ）等杂环胺络合的比色法测定Fe（II），已广泛用于分析溶液中铁的种类，这对于探讨Fenton及其相关机理至关重要。反应系统。但是，在过氧化氢的背景下，两种方法的可靠性从未得到解决。在这项研究中，我们证明Fenton系统中两种方法都可能发生严重的Fe（II）高估，特别是对于Phen方法。孵育条件的系统变化表明，将比色试剂与样品混合后，可用的Fe（II）浓度很大程度上取决于孵育时间。而且，它对pH和温度以及Fe（III），H的初始浓度高度敏感₂ O ₂和醋酸盐缓冲液。实验结果和模拟结果表明，Fe（II）的高估主要是由于分析过程中残留的H ₂ O ₂减少了Fe（III）-Phen或Fe（III）-FZ配合物的还原，该反应由配体促进杂环胺的场效应。对于存在H ₂ O _2时方法不稳定和不准确的有效补救措施，是向培养混合物中添加NH ₄ F（Phen为55 mM，FZ为35 mM），这会将残留的Fe（III）转化为无色且对还原不敏感的氟化物络合物。