Determination of Reduced and Oxidized Coenzyme Q in Canine Plasma and Heart Tissue by HPLC-ECD: Comparison with LC-MS/MS Quantification.

Coenzyme Q (Q) plays an important role in mammals for energy production in the mitochondria, and as a potent antioxidant. Oxidation ratio (% oxidized in relation to total Q) has been proposed as an important biomarker. A sensitive and reproducible HPLC-ECD method was developed for determination of reduced and oxidized Q in canine plasma and heart tissue. Chromatographic separation was achieved in 10 min using a Waters Nova-pak C column and a mobile phase with lithium perchlorate in ethanol/methanol/2-propanol. The validation showed satisfying results. Excellent linear correlation was found ( > 0.9997), intra- and inter-day precisions were below 6.5% ( = 5) and recoveries were between 89 and 109% ( = 5). Sensitivity stated as Lower Limit of Quantification (LLOQ) was 10 nM. Acceptable stability of both extracted and un-extracted samples was observed. The plasma concentration range of total Q was found to be between 0.64 and 1.24 µg/mL. Comparison with a developed LC-MS/MS method showed a correlation of = 0.85 for reduced Q and = 0.60 for oxidized Q ( = 17). However, average results were around 30% lower for ubiquinol using the LC-MS/MS method as compared with the HPLC-ECD analysis. The two methods are therefore not considered to be interchangeable.