Spectrophotometric determination of pyridoxine hydrochloride in pharmaceutical samples

A spectrophotometric method is described for the determination of pyridoxine based on the formation of an azo dye by the reaction between pyridoxine and diazotised p-nitroaniline followed by reaction of this azo dye with mercury(II) to form a stable complex. Minerals, sugars and several vitamins do not interfere when present in amounts usually found in pharmaceutical preparations. The interference from ascorbic acid was eliminated by its pre-separation as lead ascorbate. The molar absorptivity of the coloured complex is 4.6 × 104 l mol-1 cm-1 at 530 nm and Beer's law is obeyed in the range 0-80 μg of pyridoxine hydrochloride. The procedure is simple and rapid and is suitable for the routine determination of pyridoxine hydrochloride.