This research details the principal characteristics of a new chemical reaction for the determination of tocopherols (vitamin E). The proposed technique is based on the reduction of Cu(II) to Cud) by the tocopherols. The reduced ion is then available to form a complex with 2,2'-biquinoline (cuproine) and with 2,9-dimethyl - 4,7-diphenyl-l,10-phenanthroline (bathocuproine), which have maximum absorbances at 545 and 478 nm, respectively. One mole of tocopherol reduces 2 moles of copper. When urea is used as a catalyst in the reaction, α-tocopherol and γ-tocopherol react completely in 10 s; δ-tocopherol reacts in 90 s. The reaction is not affected by exposure to light. The method was compared with 2 other methods: reduction of Fe(III) to Fe(II) and complexation with 2,2'-bipyridine (conventional Emmerie- Engel method), and reduction of the free radical l,l'-diphenyl-2-picrylhydrazyl (DPPH) to the corresponding hydrazine. Absorptivities of the complexes Cu(cuproine)+2, Cu(bathocuproine)+2, Fe-(bipyridine)++, and DPPH, in terms of concentration of tocopherol were: 30.89,61.87,39.91, and 48.86 Lg-1 cm-1, respectively.

This work describes a sequence of techniques for the extraction, purification, and chemical determination of tocopherols in grains, edible oils, and byproducts of oil refining. It is shown that nontocopherol reducing substances can be removed by gentle treatment with alcoholic KOH, with only slight saponification. Total tocols are determined by a new reaction with cupric ions and complexation with 2,2,-biquinoline (cuproine). It is carried out in a two-phase system, in which the upper phase (heptane) contains the lipids and the lower phase (80% ethanol) the Cu2+ ions and cuproine. The reaction occurs when the two phases are mixed by shaking for 2.5 min. The complex, Cu(cuproine)2+, forms in the 80% ethanol, and in this medium the molar absorptivity, expressed as a function of -tocopherol, is 14490 L mol™1 cm™1 at 545 nm. The two-phase system permits control of the time of reaction, eliminating the influence of liposoluble pigments remaining in the heptane phase.

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