= SEC detector response
{c}
A <SEC detector response> must be specified before interpreting a peak area. <Ultraviolet> <absorbance> depends on a species' response factor and <concentration>, as described by the <Beer-Lambert law>; differential <refractive index> detection depends on how the dissolved species changes <refractive index>. Equal amounts need not produce equal signal areas across unlike species.
Even a calibrated mass-proportional trace is not a chain-count <probability distribution>. In an original two-population example, equal recovered <masses> of chains with <molar masses> $20{,}000$ and $80{,}000\,\mathrm{g\,mol^{-1}}$ contain four times as many chains in the lighter population. Thus equal signal areas, assuming equal response per unit <mass>, correspond to number fractions $4/5$ and $1/5$: their <number-average molar mass> is $32{,}000\,\mathrm{g\,mol^{-1}}$, while their <weight-average molar mass> is $50{,}000\,\mathrm{g\,mol^{-1}}$. Converting a continuous trace additionally requires response correction and the appropriate <change of variables> between elution and <molar mass> bins.
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