Differential pulse polarographic determination of pyruvate by “in situ” reaction with Girard-P reagent

Summary

Pyruvic acid condenses with Girard-P reagent to form a hydrazone derivative (PAHPy). From the present polarographic investigations, it was deduced that the two d.p. waves (Ep₁ = −0.76 V and shoulder-like peak Ep₂ = −1.06 V at pH = 4.5) probably correspond to two kinds of species in equilibrium: the cyclized lactonic form and the open form of the hydrazone, respectively. The first wave is more appropiate for quantification owing to its higher sensitivity, and in this way pyruvic acid was determined in the concentration range 2.5 × 10⁻⁵ to 0.035 mol/l at pH 2.4.

Carbohydrates, alcohols and carboxylic acids except α-ketoacids show tolerance limits of a least 10 times the amount of pyruvic acid (mg).

The method was satisfactorily applied to evaluate the pyruvate content of milk.