= Autoxidation inhibition period
An \b[autoxidation inhibition period] is a defined interval during which oxidation is suppressed relative to a matched uninhibited reaction. In an <inhibited autoxidation assay>, it can report how long a <radical-trapping antioxidant> retains effective capacity, but the operational start and end of the interval must be specified.
For a limiting model with antioxidant concentration $C_{A0}$, trapping stoichiometry $n$ and constant effective chain-initiation rate $R_i$, let $K_0=nC_{A0}$. If trapping is rapid and quantitative until exhaustion,
$$
t_{\rm ind}=\frac{K_0}{R_i}.
$$
At chosen values $C_{A0}=10\,\mathrm{\mu M}$, $n=2$ and $R_i=0.10\,\mathrm{\mu M\,s^{-1}}$, the model gives $200\,\mathrm s$. Equal periods can arise from different combinations of concentration, stoichiometry and initiation rate, so an independent <autoxidation initiation-rate calibration> is needed to infer a capacity.
For changing initiation rate, capacity is consumed according to the integrated flux:
$$
K_0=\int_0^{t_{\rm ind}}R_i(t)\,\mathrm dt.
$$
An original decaying-flux example takes $R_i(t)=R_0e^{-kt}$, with $k>0$. Then
$$
t_{\rm ind}=-\frac1k\log\left(1-\frac{kK_0}{R_0}\right)
$$
when $0<kK_0/R_0<1$. For $R_0=0.10\,\mathrm{\mu M\,s^{-1}}$, $k=0.002\,\mathrm{s^{-1}}$ and $K_0=20\,\mathrm{\mu M}$, this gives about $255.4\,\mathrm s$, rather than the initial-rate approximation $200\,\mathrm s$.
<Initiator-limited antioxidant exhaustion> arises because this model supplies only total flux $R_0/k$. Here that limit is $50\,\mathrm{\mu M}$: a capacity $60\,\mathrm{\mu M}$ would never be exhausted by this modeled initiation source. Absence of a breakpoint would not demonstrate unlimited antioxidant capacity.
Experimentally, a delay can be defined by a stated curve-fitting or threshold rule, while the suppressed region can retain a nonzero oxidation slope. Primary spectrophotometric co-autoxidation work treats kinetics and stoichiometry as distinct properties of the radical-trapping reaction.<A Continuous Visible Light Spectrophotometric Approach To Accurately Determine the Reactivity of Radical-Trapping Antioxidants by Evan A. Haidasz and others>[Indexed abstract, continuous reaction monitoring and kinetic/stoichiometric distinction]{ref} A longer apparent period can also reflect changed initiation, oxygen depletion or a readout effect. Comparing a matched blank, a reference antioxidant and a concentration series helps test which interpretation is supported.
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