Polarographic determination of ascorbic acid, riboflavin, pteroylglutamic acid, 2-methyl-1,4-naphthohydroquinone diacetate, thiamine, niacinamide and thiamine propyl disulfide in multivitamin preparations.

Abstract

Ascorbic acid, riboflavin and pteroylglutamic acid in multi-vitamin preparations can be concurrently determined by polarography in phosphate buffer solution (pH 6.8). The first is represented by its anodic wave at E1/2-0.05V and the next two by their cathodic waves at E1/2-0.47 and -1.2V vs NCE, respectively. The reduction wave at E1/2 -0.41V in 0.1N HCl solution is also utilized for the determination of pteroylglutamic acid in the mixture. 2-Methyl-1, 4-naphthohydroquinone diacetate (K) is determined by means of the redox wave of menadione which is formed by alkali hydrolysis of K. Thiamine in such preparations is determined by the maximum wave which is observed at ca. -1.5V in its solution containing 1mM CoCl2, 0.1M NH4Cl and 0.1M NH3.The determination of niacinamide is effected by means of its cathodic wave at -1.8V in 0.1N NaOH. Thiamine propyl disulfide (TPD) in a mixture of TPD, thiamine, riboflavin and “Tween” is determined by means of the reduction wave at E1/2 -0.7V in pH 4 acetate buffer, in which condition riboflavin is also determined by its wave at E1/2 -0.34V. Thiamine in such a mixture is determined by means of its anodic wave at E1/2 -0.44V in pH 10-12 phosphate buffer.