Determination of coenzyme Q in human plasma

Coenzyme Q10 (CoQ10) levels in human plasma were determined by high-performance liquid chromatography (HPLC) with UV detection. CoQ10 was dissociated from lipoproteins by methanol and subsequently cleaned-up on silica gel and octadecyl silica solid-phase extraction cartridges. HPLC separation was performed on a C18 reversed-phase column. The methanol-hexane mobile phase provided a greater possibility of separation procedure adjustment allowing the shortest possible elution time without loss of resolution than a two-alcohol mobile phase. Quantitation was based on the peak heights using a standard addition method. The lower limit of detection was 8 ng on-column, corresponding to 90 micrograms ubiquinone per litre of plasma in an actual sample. Thirty-one randomly selected plasma samples from apparently healthy, 18 to 56-year-old individuals (males and females) were analyzed for total CoQ10. The average level in these subjects was 0.47 +/- 0.18 mg/l with the range of 0.26-1.03 mg/l. The method was also applied to the determination of ubiquinone plasma level changes in one healthy volunteer over a period of one month and after oral intake of CoQ10.