A method for the determination of the pKa of alpha-N-benzoyl-L-arginine in the presence of an impurity.

A sensitive and specific assay method for allantoin is described together with its application to rat plasma. The method consists of two main successive steps: hydrolytic formation of glyoxylic acid from allantoin, and fluorometric measurement of NAD produced from the reaction of glyoxylic acid and NADH, catalyzed by glyoxylate reductase. As little as 0.1 μg of allantoin can be determined. For the determination of endogeneous allantoin levels in rat plasma, 50 μl of the plasma is sufficient. Due to the higher sensitivity and specificity, the proposed method has advantages over the colorimetric method which has long been used for the determination of allantoin.