| Abstract: | ABSTRACT A flow-injection (FI) procedure is proposed for the determination of pyridoxine. In the FI manifold, a solution of p-sulfanilic acid in a micellar medium of N-cetylpyridinium chloride (NCPC) was diazotized with nitrite in acidic medium, and the pH was then adjusted to 7 with monohydrogenphosphate; the sample was injected into this stream and the absorbance measured at 450 nm. The surfactant catalyzed the derivatization reaction and enhanced the sensitivity 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 optimized FI conditions, the calibration curve was linear from the limit of detection, 5×10?5 M, up to 1×10?3 M, and the sampling frequency was 60 h?1. The procedure was applied to the determination of pyridoxine hydrochloride in commercial pharmaceutical preparations, with recoveries close to 100%. |
