Method for the determination of vitamin K1(20) in human plasma by stable isotope dilution/gas chromatography/mass spectrometry.

A method for the quantitative determination of vitamin K1(20) (VK), an essential cofactor in the carboxylation of clotting factors, is presented. The assay is based on gas chromatography/electron impact mass/spectrometry. The preparation of deuterium-labelled vitamin K1(20) for use as an internal standard is described. The method involves extraction of VK from human plasma and its derivatization to the heptafluorobutyryl ester after reduction of one carbonyl group with zinc. The detection limit was found to be 1.0 pg and the limit of quantitation 2.0 pg ml-1 plasma. This permits the measurement of vitamin K1(20) even in small quantities of plasma, which is highly desirable in investigations dealing with clotting abnormalities in neonates and infants.