The construction and general performance characteristics of two novel potentiometric PVC membrane sensors responsive to the pyridoxine hydrochloride known as vitamin B6 (VB6) are described. These sensors are based on the use of the ion-association complexes of the pyridoxine cation with molybdophosphate and tungstophosphate counter anions as ion pairs in a plasticized PVC matrix. The electrodes show a stable, near-Nernstian response for 6 × 10–5–1 × 10–2 M VB6 at 25°C over the pH range 2–4 with a cationic slope of 54.0 ± 0.5 and 54.5 ± 0.4 mV per concentration decade for pyridoxine–molybdophosphate and pyridoxine–tungstophosphate, respectively. The two electrodes have the same lower detection limit (4 × 10–5 M), and the response times are 45–60 and 30–45 s in the same order for both. Selectivity coefficients for VB6 relative to a number of interfering substances were investigated. There is negligible interference from many cations, some vitamins, and pharmaceutical excipients. The determination of VB6 in some pharmaceutical preparations using the proposed electrodes gave an average recovery of 98.0 and 99.0% of the nominal value and a mean standard deviation of 1.1 and 0.9% (n = 3) for pyridoxine–molybdophosphate and pyridoxine–tungstophosphate electrodes, respectively. The results compare favorably with data obtained by the British pharmacopoeia method.
