POLAROGRAPHIC STUDY - REACTION OF VITAMINS-K WITH THIOLS AND THE CONSECUTIVE DETERMINATION OF THE K-VITAMINS

The reactions of the K vitamins and eight thiols were studied by polarography in 80% ethanol in the apparent pH range 3-10. In the absence of oxygen, thiols react with vitamin K3, at the 3-position to form naphthohydroquinones with a thioether linkage. The general reaction mechanism was confirmed by electrochemical and spectrophotometric measurements. Vitamins K1 and K2 do not react. The consecutive determination of K3 and K1 (or K2), whose polarographic reduction waves completely overlap, can be achieved by measurement of the total wave height, then adding excess of thioglycolic acid at pH 6.2, which results in the complete disappearance of the diffusion current of K3. This enables K1 (or K2) to be determined, and hence K3 by difference. © 1979.