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%.