Simultaneous determination of ascorbic acid, pyridoxine hydrochloride, and tyrosine by derivative UV spectrophotometry.

A new UV spectrophotometric method for resolving a three-component drug mixture of ascorbic acid (I), pyridoxine hydrochloride (II), and tyrosine (III), on the basis of the first-derivative UV spectra and zero-crossing technique, is described. Beer's law was obeyed in the concentration range of 7.0-15.0, 0.25-1.0, and 8.0-40.0 micrograms/ml for I, II, and III, respectively. Lower limits of detection at the 95% confidence level were 2.88, 0.69, and 5.43 micrograms/ml, respectively. The advantages of the proposed method (speed, easy sample preparation, and lower cost per analysis) also include its application to the content uniformity and dissolution test of a three-component mixture of drugs.