The Polarographic Behavior of Several α-Keto Acids in Buffered Solutions Containingo-Phenylenediamine, and Its Analytical Application

Abstract Such a-keto acids as glyoxylic (I), pyruvic (II), α-ketobutyric (III), mesoxalic (IV), oxalacetic (V), and α-ketoglutaric acid (VI) condense with o-phenylenediamine (OPD) to form two kinds of products, depending on the pH values of the reaction mixtures. The condensation product formed at pH values lower than 4 gives a well-defined reduction wave (E1⁄2 vs. SCE at pH 2.0: −0.490 V for I, −0.587 V for II, −0.592 V for III, −0.181 V for IV, −0.590 V for V, and −0.576 V for VI) at a potential more positive than that of free α-keto acid, while the other product, formed at pH values between 4 and 8, gives an oxidation wave (E1⁄2:−0.1–−0.2 V vs. SCE for all α-keto acids at pH 6.0). From the present polarographic investigations, it was deduced that the condensation product giving the reduction wave is probably 2-hydroxyquinoxaline derivatives and that the product giving the oxidation wave is benzimidazoline derivatives. A linear relation was obtained between the wave height for the reduction of the condensation product and the concentration ((0.5–20)×10−4 m) for each α-keto acid under appropriate conditions. The reduction wave of the condensation product was used for the determination of II in a commercial product containing II as an impurity.