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流动注射滴定法(简称FIA滴定),在高分散体系中进行,原则上可用于各类滴定反应。但至今有关FIA滴定的工作报道还不多见。本文把FIA滴定用于氧化还原滴定。用重铬酸钾法测定铁的含量已成为公认的标准方法,其中预先还原Fe(Ⅲ)的步骤可采用SnCl_2-HgCl_2法或无汞还原法。另外,还可用金属还原柱进行直接还原。但后者由于操作麻烦而较少应用。此外,为了定量还原Fe(Ⅲ),通过还原柱的流速不宜快,这样难免会引起部分Fe(Ⅱ)再度被氧化的可能。在我们工作中,由于FIA体系为一封闭体系,可避免Fe(Ⅱ)的现氧化。另外,FIA所测量的为非平衡信号,这样,采用短的还原柱,只要还原效率恒定不变,即使未达到100%还原,仍能获得重现性良好的分析结果。
Flow injection titration (FIA titration), carried out in highly dispersed systems, in principle, can be used for various types of titration reaction. But so far reports on the FIA titration work is still rare. In this paper, FIA titration is used for redox titration. The determination of iron content by the potassium dichromate method has become the accepted standard method, wherein the step of reducing the Fe (III) in advance can adopt SnCl 2 -HgCl 2 method or mercury-free reduction method. In addition, you can also use metal reduction column for direct reduction. However, the latter is less used due to operational troubles. In addition, in order to quantitatively reduce Fe (Ⅲ), the velocity of flow through the reduction column should not be too fast, which will inevitably lead to the possibility of partial oxidation of Fe (Ⅱ) again. In our work, since the FIA system is a closed system, the oxidation of Fe (II) can be avoided. In addition, the FIA measures the unbalanced signal, so that with a short reduction column, good reproducibility of the analysis results can be obtained, even if the reduction efficiency is not changed to 100%.