Citric acid and oxalic acid are present in many products, such as foods or chemical solvents (e.g., decontamination solutions). Both acids are reducing agents, and citric acid is additionally a powerful antioxidant.

Both of these acids can be individually determined using titration. However, to determine their concentrations in mixtures, a content calculation is only possible with correction factors for each acid due to their mutual impact (buffer effect).

A fast and accurate determination of these acids in various mixtures by potentiometric titration using the dEcotrode plus and sodium hydroxide as titrant can be realized. This Application Note explains more about this fast and easy analysis with reliable, automated titration instruments from Metrohm.

The analysis is demonstrated on a mixture of citric acid and oxalic acid (β(citric acid) = 20 g/L and β(oxalic acid) = 20 g/L).

No sample preparation is required.

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.