In this study, the use of potassium dichromate as a oxidizing reagent in the 3-step chemiluminescence (CL) chemical oxygen demand (COD) method, which based on the principle of permanganate COD (COD_Mn) method (JIS K0102), was developed (3-step CL COD_Cr method). The sample reacted with in exceed of dichromate under heating, the remaining dichromate was neutralized by a reducing organic compound. Then, the remaining amount of the reducing organic compound was detected in the CL detector using permanganate CL reagent. Six organic compounds: gallic acid, phenol, pyrocatechol, ascorbic acid, pyrogallol, and potassium hydrogen phthalate were investigated as the reducing organic compounds. The CL kinetics of these compounds with acidic permanganate reagent were studied, and pyrogallol showed the highest signal with the relevant fastest response. Hence, pyrogallol is chosen as the reducing organic compound. The enhancement effects of seven metal ions: Cr(III), Mn(II), Cu(II), Ag(I), Fe(II), Fe(III), and Mg(II) were investigated. The result shows that Cr(III), Mn(II), Fe(II), and Fe(III) enhanced the signal. Fe(II) and Fe(III) show the highest enhance effects, the signals increase to 188 % and 205 %, respectively. However, Fe(II) makes the permanganate reagent become less stable due to the reaction between Fe(II) and permanganate and the enhancement decreased significantly with time. Hence, Fe(III) was added to the permanganate reagent at the optimum concentration of 0.45 mmol dm-3. The correlation between 3-step CL COD_Cr method and the conventional COD_Mn for several organic compounds showed good determination coefficient R² = 0.9594 (n=16). The limit of detection was 0.083 mg/L, using gallic acid as a standard. The method was applied to measurement of river water samples, the results are in good correlation with COD_Mn method.

中文翻译：

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重铬酸盐氧化试剂测定化学需氧量的三步化学发光法

本研究基于高锰酸盐化学需氧量（COD _Mn）方法（JIS K0102）的原理，开发了在三步化学发光（CL）化学需氧量（COD）方法中使用重铬酸钾作为氧化剂的方法。（3步CL COD _Cr方法）。样品在加热下与过量的重铬酸盐反应，剩余的重铬酸盐被还原性有机化合物中和。然后，使用高锰酸盐CL试剂在CL检测器中检测还原性有机化合物的残留量。研究了六种有机化合物：没食子酸，苯酚，邻苯二酚，抗坏血酸，邻苯三酚和邻苯二甲酸氢钾作为还原性有机化合物。研究了这些化合物与酸性高锰酸盐试剂的CL动力学，并且邻苯三酚显示了最高的信号和相应的最快响应。因此，选择邻苯三酚作为还原性有机化合物。研究了Cr（III），Mn（II），Cu（II），Ag（I），Fe（II），Fe（III）和Mg（II）等7种金属离子的增强作用。结果表明，Cr（III），Mn（II），Fe（II），Fe（III）增强了信号。Fe（II）和Fe（III）表现出最高的增强效果，信号分别增加到188％和205％。然而，由于Fe（II）与高锰酸盐之间的反应，Fe（II）使高锰酸盐试剂变得不稳定，并且增强作用随时间显着降低。因此，将Fe（III）以0.45 mmol dm-3的最佳浓度添加到高锰酸盐试剂中。三步CL COD之间的相关性_Cr法和常规的COD _Mn对几种有机化合物的测定系数R ² = 0.9594（n = 16）。以没食子酸为标准，检测下限为0.083 mg / L。该方法用于河流水样的测定，结果与COD _Mn法具有很好的相关性。