Microelectrode Studies of Tertiary Amines in Organic Solvents: Considering Triethanolamine to Estimate the Composition of Acetic Acid–Ethyl Acetate Mixtures

Four tertiary amines (tributylamine, tripentylamine, trihexylamine, triethanolamine) were investigated with a 25 μm platinum disc microelectrode in more organic solvents. In the commonly used inert solvent acetonitrile, the sigmoidal-shaped curves used were recorded, except for triethanolamine, which showed two current plateaus close to each other, indicating temporal blocking in this case. The really surprising results arose from studies in acetic acid and ethyl acetate. Due to the complete protonation in acetic acid, the significant shifts of oxidation potentials led to the acquisition of lower currents only with the rising parts also using the same potential window as in ethyl acetate, where the voltammograms had a sigmoidal shape. Triethanolamine exhibited significant electrode deactivation in ethyl acetate, leading to the appearance of peak-shaped curves, and the difference between the first and second voltammograms was large. The current difference between the first and second scans allowed consequences for acetic acid content in cases where it was small, as the choice of this parameter proved to be the best for the analytical task. On the other hand, the differences in the shape of voltammograms allowed for quantitative approximations. The observed phenomenon could be utilized only for the estimation of acetic acid content.