ascorbic acid is specifically quantified by pretreating one of a pair of replicate samples with ascorbate oxidase ( ec 1.10.3.3 ) , to oxidize the ascorbic acid , then reacting both samples with fe3+-tptz and measuring the difference between the absorbances at 593 nm of the treated and untreated samples .
C0003967
ascorbate oxidase
C0030016
ec 1