チオグリコール酸との反応を利用するビタミンK類の分離定量

抄録

Consecutive determination of vitamin K's by their reaction with some thiol compounds has been examined by polarography in 80% ethanol containing acetate buffer and sodium perchlorate. Vitamin K₁ (Ib), K₂ (Ic), and K₃ (Ia) exhibited well-defined polarographic reduction waves in this medium, but their half-wave potentials were so close together that these vitamins cannot be determined simultaneously by a conventional polarography. In the absence of oxygen in solution, Ia reacts with thiol compounds to form naphthohydroquinones having a thioether linkage, while, Ib and Ic do not react with thiol compounds as a result of an interference of the alkyl substituents at both 2- and 3- positions in these vitamins. These facts can be applied to the consecutive determination of Ia and Ib (or Ic). The total concentration of Ia and Ib (or Ic) in solution is easily obtained by the measurement of the height of the reduction wave. The addition of thiol compounds to the solution gives no effect on the diffusion current of Ib (and also of Ic) but causes a significant decrease in that of Ia. Then the addition of an excess amount of thiol compounds results in the complete disappearancd of the diffusion current of Ia, and consequently the concentrations of Ia and Ib (or Ic) are determined. Among the thiol compounds used in this experiment, the use of thioglycolic acid in the solution of pH at around 6.2 was found to be the most suitable for the present purpose. This method was applied to the mixed solutions of Ia-Ib and Ia-Ic with satisfactory results.