エタノール-水混合溶媒中におけるビタミンK_3とシステインの反応と, ビタミンK類の分離定量

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The reaction of vitamins K with cysteine was studied by polarography in 90% ethanol. Vitamins K_1,K_2,and K_3 exhibit well-defined polarographic reduction waves in this medium. In the presence of cysteine in solution, the addition of SH group takes place at 3-position of naphthoquinone ring in vitamin K_3. As a result of this reaction, the diffusion current of vitamin K_3 decreases markedly with the increasing concentration of cysteine, and new reduction waves appear at a more negative potential region. The change in the polarogram of vitamin K_3 caused by cysteine is affected by oxygen dissolved in the solution. Possible reaction mechanisms in the presence and absence of oxygen were discussed. On the other hand, cysteine does not affect the polarograms of vitamins K_1 and K_2 because the formation of addition compounds is hindered by the alkyl groups in both 2- and 3-positions of these vitamins. Vitamins K cannot be determined simultaneously by the conventional polarography because of their very close half-wave potentials. The experimental results in the present work is applicable to the consecutive determination of vitamins K_1 (or K_2) and K_3. The total concentration of vitamins K is easily obtained by the measurement of the height of the reduction wave. The diffusion current of vitamin K_3 disappears completely within 20 min by the Addition of an excess amount of cysteine to the solution, while that of vitamin K_1 (or K_2) remains unchanged irrespective of cysteine concentration, and consequently, both the concentrations of vitamin K_1 (or K_2) and K_3 are determined. This method has been applied to the mixed solutions of K_1-K_3 and K_2-K_3 with satisfactory results.
公益社団法人日本薬学会の論文
1974-09-25

エタノール-水混合溶媒中におけるビタミンK_3とシステインの反応と, ビタミンK類の分離定量

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