Quantification of the Reduced Form of Coenzyme Q10, Ubiquinol, in Dietary Supplements with HPLC-ESI-MS/MS

Presence of reduced ubiquinone, ubiquinol, in dietary supplements can originate either from the reduction of ubiquinone due to the co-formulation processes with reducing agents or intentional addition of ubiquinol. As the amount of ubiquinol influences the analytical techniques intended for total ubiquinone determination and the positioning of dietary supplements, the quantification of ubiquinol can be a prerequisite in the quality control process of the related products. In our study, a comprehensive method development has been carried out including (i) the production of ubiquinol together with its HPLC-ESI-MS/MS based verification, (ii) the monitoring of ubiquinol oxidation during the extraction process, (iii) a novel spiking method to validate ubiquinol calibration and (iv) the determination of analyte recovery with an HPLC-UV technique. The combined method was used to quantify ubiquinol in 12 dietary supplement samples containing 31.5-104.5 mg total Q(10) g(-1). The range of ubiquinol content was 5-16 % related to total ubiquinone concentration and the extraction efficiency values exceeded 99.6 % in all cases.