@article{discovery348,
          number = {5},
          volume = {46},
           month = {May},
            year = {2005},
         journal = {The Journal of Lipid Research},
           title = {Determination of the urinary aglycone metabolites of vitamin K by HPLC with redox-mode electrochemical detection},
            note = {Imported via OAI, 9:29:00 10th May 2005},
           pages = {1053--1060},
            issn = {0022-2275},
             url = {https://discovery.ucl.ac.uk/id/eprint/348/},
          author = {Harrington, DJ and Soper, R and Edwards, C and Savidge, GF and Hodges, SJ and Shearer, MJ},
        abstract = {We describe a method for the determination of the two major urinary metabolites of vitamin K as the methyl esters of their agyclone structures, 2-methyl-3-(3-3-carboxymethylpropyl)-1,4-naphthoquinone (5C-side-chain metabolite) and 2-methyl-3-(5-carboxy-3-methyl-2-pentenyl)-1,4-naphthoquinone (7C-side-chain metabolite), by HPLC with electrochemical detection (ECD) in the redox mode. Urinary salts were removed by reversed-phase (C18) solid phase extraction (SPE) and the predominately conjugated vitamin K metabolites hydrolysed with methanolic HCl. The resultant 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 post-column coulometric reduction at an upstream electrode. The assay gave excellent linearity (r2 typically = 0.999) and high sensitivity with an on-column detection limit of {\ensuremath{<}}3.5 fmol ({\ensuremath{<}}1pg). The inter-assay precision was typically 10\%. Metabolite recovery was compared to that of an internal standard (2-methyl-3-(7'-carboxy-heptyl)-1,4-naphthoquinone), added to urine samples just before analysis. Using this methodology we confirmed that the 5C- and 7C-metabolite were major catabolites of both phylloquinone (vitamin K1) and menaquinones (vitamin K2) in humans. We propose that the measurement of urinary vitamin K metabolite excretion is a candidate non-invasive marker of total vitamin K status.}
}