Chemicals and reagents. Ammonium molybdate;
ascorbic acid; reduced glutathione; butyl hydroxytoluene
(BHT);3 a-, g-, and d-tocopherol; and the internal
standard a-tocopherol acetate were obtained from
Sigma (St. Louis, MO). HPLC grade methanol, hexane,
ethanol, dimethyl sulfoxide, and analytical grade sodium
phosphate and sulfuric acid were from Merck
(Darmstadt, Germany). All other chemicals were of
analytical grade.