= Evan A. Haidasz
{c}
\b[Evan A. Haidasz] is first author of a spectrophotometric method for measuring <radical-trapping antioxidant> reactivity, with <Antonius T. M. Van Kessel> and <Derek A. Pratt>. The primary paper uses visible-light monitoring of hydrocarbon co-oxidation with <PBD-BODIPY> or <STY-BODIPY> signal carriers.<A Continuous Visible Light Spectrophotometric Approach To Accurately Determine the Reactivity of Radical-Trapping Antioxidants by Evan A. Haidasz and others>[Byline and Abstract; Journal of Organic Chemistry81, pp.737–744]{ref} The measurement connects a continuous optical trace with a kinetic model, rather than ranking compounds solely by a final colour.
For an original idealization, let a signal carrier at concentration $c(t)$ obey the <Beer-Lambert law> in a fixed path:
$$
A(t)=A_0+\epsilon\ell c(t),\qquad
-\frac{\mathrm dc}{\mathrm dt}=-\frac1{\epsilon\ell}\frac{\mathrm dA}{\mathrm dt}.
$$
With stipulated $\epsilon=50000\,\mathrm{L\,mol^{-1}\,cm^{-1}}$, $\ell=1\,\mathrm{cm}$ and slope $-0.010\,\mathrm{min^{-1}}$, the inferred carrier-consumption rate is $0.20\,\mathrm{\mu mol\,L^{-1}\,min^{-1}}$. These chosen optical parameters are not a calibration assigned to the paper's dyes.
A constant background drops out of the derivative, but a drifting background does not. If $A_0$ itself changes, its slope can mimic chemical conversion. Products that also absorb at the measurement wavelength likewise require an expanded response model. Continuous observation provides timing information, while chemical identity and calibration determine what that timing means. The inferred dye-consumption rate is not automatically the elementary rate of every radical event.
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