Simultaneous measurement of tocopherols and tocopheryl quinones in tissue fractions using high-performance liquid chromatography with redox-cycling electrochemical detection.

Tocopherols and tocopheryl quinones in lipid extracts of biological samples have primarily been measured using relatively insensitive ultraviolet detection methods. Oxidative electrochemical detection increases both the sensitivity and selectivity when measuring the tocopherols. We have developed an electrochemical detection system which sequentially reduces and oxidizes tocopheryl metabolites eluted from a reversed-phase high-performance liquid chromatography column, achieving sensitivities of about 0.05 pmol for both the tocopherols and their quinones. Using a rapid and mild extraction procedure, endogenous levels of alpha- and gamma-tocopherol as well as their respective quinones were measured in homogenates of chicken liver and muscle, and in dilute preparations of rat liver microsomes. The principle of the detection system could be applied to the determination of tocopheryl dihydroquinones, ubiquinols and ubiquinones with slight modifications to the mobile phase buffer and the electrode potentials of the detector.