Flow-injection analysis of pyridoxine hydrochloride by coupling with the diazonium ion of p-sulfanilic acid

A flow-injection (FI) procedure is proposed for the determination of pyrido xine. In the FI manifold, a solution of p-sulfanilic acid in a micellar med ium of N-cetylpyridinium chloride (NCPC) was diazotized with nitrite in aci dic medium, and the pH was then adjusted to 7 with monohydrogenphosphate; t he sample was injected into this stream and the absorbance measured at 450 Mn. The surfactant catalyzed the derivatization reaction and enhanced the s ensitivity of the FI procedure. Consequently, the addition of toxic mercury (II) acetate, used in the conventional procedure performed in non-micellar medium, was no longer required. The signals obtained with other surfactants , such as sodium dodecyl sulfate or Triton X-100, were smaller. Under optim ized FI conditions, the calibration curve was linear from the limit of dete ction, 5x10(-5) M up to 1x10(-3) M, and the sampling frequency was 60 h(-1) . The procedure was applied to the determination of pyridoxine hydrochlorid e in commercial pharmaceutical preparations, with recoveries close to 100%.