Overlapping ionization constants for cefotaxime

The attribution of three ionization constants (2.1, 3.4, and 10.9) for cefotaxime has been made, based on potentiometric titration and UV absorption data simultaneously. Two overlapping constants were found (2.1 and 3.4) and attributed to the carboxyl group in the 4 position and to the aminothiazole nucleus, respectively.