使用校正因子的可靠电位滴定法

柠檬酸和草酸存在于许多产品中，例如食品或化学溶剂（例如去污溶液）。这两种酸都是还原剂，柠檬酸是另外一种强大的抗氧化剂。

这两种酸都可以用滴定法单独测定。然而，为了确定它们在混合物中的浓度，由于它们的相互影响（缓冲效应），只有使用每种酸的校正系数才能进行含量计算。

使用Decorode plus和氢氧化钠作为滴定剂，通过电位滴定法可以快速准确地测定各种混合物中的这些酸。本应用说明详细介绍了使用Metrohm可靠的自动滴定仪器进行快速简便的分析。

样品和样品制备

在柠檬酸和草酸（β（柠檬酸）=20 g/L和β（草酸）=20 g/L）的混合物上进行了分析。

无需样品制备。

实验

分析是在OMNIS自动机器人处理装置上完全自动进行的，该机器人与OMNIS高级自动电位滴定仪和dEcotrode plus相结合，用于指示。

将样品溶液转移到样品烧杯中，并添加去离子水。用标准氢氧化钠滴定溶液，直到第二个等效点之后。每次滴定后，将溶液吸入，然后用去离子水冲洗电极。

RESULTS

Reproducible titration curves (see Figure 2) are obtained for all analyses. The first equivalence point corresponds to oxalic acid and the second to citric acid. However, the two obtained equivalence points influence each other due to the close pKa values of the acids (oxalic acid = 1.25 and 4.14, citric acid = 3.13, 4.76, and 6.39). Therefore, a correction factor is required for the titration. The correction factors used for this sample are 0.904 for citric acid, and 1.11 for oxalic acid.

The automated analysis leads to reproducible results with a RSD < 1.5% as shown in Table 1.

CONCLUSION

As a non-linear-correlation between the correction factors and the ratio of citric acid and oxalic acid exists, it is recommended to determine the correction factors at the expected ratio of citric and oxalic acid using standard solutions.

However, this method provides an easy and fast way to determine the citric acid and oxalic acid content in mixtures by potentiometric titration. The determination of the factors can be done automatically using the OMNIS system.