Voltammetric determination of vitamins in a pharmaceutical formulation

Direct current polarography and differential pulse polarographic methods have been developed for the qualitative as well as quantitative analysis of vitamin B1, B2 and B6. Thiamin (vitamin B1) produced a well-defined wave in 0.1 M KCl at pH 5.2 with E(1/2)=-1.2 V and E(p)=-1.22 V versus saturated calomal electrode (SCE). Riboflavin (vitamin B2) gave two distinct waves in Britton Robinson buffer at pH 1.8 with E(1/2) values=-0.13 and -0.34 V versus SCE and at pH 6.5 with E(1/2)=-1.10 V and E(p)=-1.2 V versus SCE. Pyridoxin (vitamin B6) produced a well-defined wave in Britton Robinson buffer at pH 6.5 with E(1/2)=-1.7 V and E(p)=-1.68 V versus SCE. All the three vitamins under study are reversibly reduced at the electrode surface. The number of electrons involved in the electrode process for vitamin B1 and B6 is one in each case where as for the two waves of B2 it is one and two, respectively. This has been confirmed by the measurement of E(3/4)-E(1/4) values and also from the log plot slopes for the reduction waves. The wave height of polarogram was found to be proportional to the vitamin concentration. The developed methods have been standardised for the determination of these compounds in pharmaceutical formulation. The concentration of vitamin B1, B2 and B6 are found to be 9.96, 9.92 and 3.01 mg, respectively in 240 mg of capsule powder of a standard company (name has not been disclosed due to secrecy purpose). The results have been found to be in excellent agreement to that claimed by the manufacturer. The observed data has been subjected to statistical analysis, which revealed high reliability and precision.