出版社：American Society for Biochemistry and Molecular Biology
摘要：We describe a method for the determination of the two major urinary metabolites of vitamin K as the methyl esters of their aglycone structures, 2-methyl-3-(3′-3′-carboxymethylpropyl)-1,4-naphthoquinone (5C-aglycone) and 2-methyl-3-(5′-carboxy-3′-methyl-2′-pentenyl)-1,4-naphthoquinone (7C-aglycone), by HPLC with electrochemical detection (ECD) in the redox mode. Urinary salts were removed by reversed-phase (C18) solid-phase extraction (SPE), and the predominantly conjugated vitamin K metabolites were hydrolyzed with methanolic HCl. The resulting carboxylic acid aglycones were quantitatively methylated with diazomethane and fractionated by normal-phase (silica) SPE. Final analysis was by reversed-phase (C18) HPLC with a methanol-aqueous mobile phase. Metabolites were detected by amperometric, oxidative ECD of their quinol forms, which were generated by postcolumn coulometric reduction at an upstream electrode. The assay gave excellent linearity (typically, r 2 ⩾ 0.999) and high sensitivity with an on-column detection limit of 1) and menaquinones (vitamin K2) in humans. We propose that the measurement of urinary vitamin K metabolite excretion is a candidate noninvasive marker of total vitamin K status.
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