Rapid coulometry of tocopherols in ethanol and chloroform using ferricyanide ion mediator

In order to estimate the absolute determination method of tocopherols, rapid coulometry has been carried out by using a vapor grown carbon fiber electrode impregnated with ethanol-water solution containing ferricyanide ion as a mediator. The electrolysis time of 1 × l0−3 M α-tocopherol in ethanol was below 30 seconds, and its current efficiency was attained to be 100.1% when an ethanol content in pH 4.0 electrolyte is 20%. Four isomers of vitamin E in chloroform were also determined by indirect coulometry in which ferricyanide solution was mixed with sample solution for 10 minutes prior to electrolysis and the current efficiencies of α-, β-, γ-, and δ-tocopherols were obtained to be 97.6, 100.5, 89.7, and 83.7%, respectively, and the relative standard deviations were below 1%.