= A. Buursma
{c}
\b[A. Buursma] collaborated with <W. G. Zijlstra> and <W. P. Meeuwsen-van der Roest> on experimental reference spectra for <hemoglobin> derivatives. Their 1991 paper measured <molar absorption coefficients> for fetal and adult forms of the oxygenated, deoxygenated, carbon-monoxide-bound and oxidized derivatives.<Absorption spectra of human fetal and adult oxyhemoglobin, de-oxyhemoglobin, carboxyhemoglobin, and methemoglobin by W. G. Zijlstra and others>[Byline and Abstract]{ref} Such measurements support quantitative optical analysis of mixtures, including <co-oximetry>.
The measurement problem can be expressed through the <Beer-Lambert law>. For a transparent mixture with a known path length $l$, a simple linear model at wavelength $\lambda_j$ is
$$
A_j=l\sum_k\varepsilon_{jk}c_k.
$$
Here $A_j$ is <absorbance>, $c_k$ are component concentrations and $\varepsilon_{jk}$ are reference <molar absorption coefficients>. The reference experiment provides coefficients; the later mixture experiment measures the $A_j$. These are distinct roles in the analysis.
An original example illustrates why multiple independent readings are useful. With normalized coefficients, let $A_1=c_1+2c_2$ and $A_2=2c_1+c_2$. Measurements $A_1=A_2=3$ imply $c_1=c_2=1$. With only the first reading, both $(c_1,c_2)=(1,1)$ and $(3,0)$ fit. Additional readings help only when their coefficient rows supply <linear independence>; repeating the same equation more precisely does not identify both concentrations.
The example explains the importance of reliable reference coefficients without attributing an unreported individual laboratory task to <A. Buursma>. The verified scientific contribution is coauthorship of the experimental spectral dataset.
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