The complete model for the OPDA-method
involves the following processes (Fig. 1): (i) the enzymatic twostep
oxidation of ascorbic acid, involving kinetic parameters
k1, k2, and k3 (Eq. (2)), (ii) the complexation reaction of dehydroascorbic
acid with ortho-phenylenediamine (k4) (Eq. (3)), (iii)
the diffusion process of O2 from the surroundings to the wells
(k5) (Eq. (4)) and (iv) the spontaneous non-enzymatic oxidation