Spectrophotometric determination of pyridoxine hydrochloride

A spectrophotometric method is described for the determination of pyridoxine hydrochloride based on an oxidative coupling reaction with 4-aminoantipyrine in the presence of ammonium persulphate. The stable yellow colour obtained is measured spectrophotometrically at 420 nm. Minerals, sugars and several vitamins do not interfere when present in amounts usually found in pharmaceutical preparations. Modification of the method with boric acid can be used to distinguish pyridoxine from pyridoxal and pyridoxamine. Interference from ascorbic acid was eliminated by pre-separation as lead ascorbate. The molar absorptivity of the colour system is 5.41 × 103 I mol -1 cm-1 at 420 nm and Beer's law is obeyed in the range 0-250 μg of pyridoxine hydrochloride. The procedure is simple, rapid and suitable for routine determinations.