High-performance liquid chromatography (HPLC) with dual-electrode electrochemical detection has been used, in the redox mode, to determine normal and sub-normal circulating plasma levels of phylloquinone (vitamin K1) and concentrations down to 20 pg ml–1 have been measured in plasma. The coefficient of variation, for endogenous levels, was 10%(mean 330 pg ml–1; n= 6). When compared with a single glassy carbon electrode, operated in the reductive mode, the sensitivity of the dual-electrode cell was greater by at least an order of magnitude. Thus the volume of plasma required for the assay could be reduced.
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Hart et al. (1985) studied this question.