Autoxidation lag standard addition

Autoxidation lag standard addition estimates an initiation rate or an equivalent background trapping capacity by adding known amounts of a reference radical-trapping antioxidant to a matched sample matrix. It uses a series of autoxidation inhibition periods, rather than treating one delay as a chemical concentration.

Under constant effective initiation rate $R_i$, fast quantitative trapping and unchanged reference stoichiometry $n_s$, let $K_b$ be the initial background capacity and $C_s$ the added reference concentration. Capacity balance givesThus the linear regression intercept and slope have different roles. The concentration $a/b$ is an equivalent amount of the chosen reference; it does not identify the background chemical species.

For an original series, $C_s=0,4,8\mu \mathrm{M}$ gives delays $30,70,110\mathrm{s}$. Then $a=30\mathrm{s}$ and $b=10\mathrm{s}\mu {\mathrm{M}}^{-1}$. With $n_s=2$, the model gives $R_i=0.20\mu \mathrm{M}{\mathrm{s}}^{-1}$ and $K_b=6\mu \mathrm{M}$ of trapping capacity, equivalent to $3\mu \mathrm{M}$ of that reference. Using only the largest addition and dividing $n_s{C}_s$ by its full delay would give about $0.145\mu \mathrm{M}{\mathrm{s}}^{-1}$, because it incorrectly includes the background delay in the reference-only balance.

At first order, if $n_s$ is known, $u(R_i)/R_i\approx u(b)/b$. Inference of $K_b=n_{s}a/b$ also involves the fitted intercept-slope covariance; treating fitted parameters as independent can misstate the measurement uncertainty. Replicates at several concentrations test linearity and estimate the delay variability.

The chemical observation must still be defined. A primary spectrophotometric method monitors a BODIPY-based signal carrier co-autoxidizing with a hydrocarbon and distinguishes trapping kinetics from stoichiometry.^[ref] The regression above is a stated capacity model, not an assertion that this paper used this particular numerical series. Keep solvent addition, initiation, temperature, oxygen supply and breakpoint rule matched. Curvature can reveal altered chemistry, oxygen-limited autoxidation or time-varying initiation; it should not be hidden by forcing a straight line.