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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.^[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 ${\lambda }_j$ isHere $A_j$ is absorbance, $c_k$ are component concentrations and ${\epsilon }_{jk}$ 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.

W. G. Zijlstra is the first author of a 1991 study with A. Buursma and W. P. Meeuwsen-van der Roest measuring visible and near-infrared reference spectra of human hemoglobin derivatives. The authors reported that small fetal/adult differences in molar absorption coefficient mattered for multicomponent analysis.^[ref] The work connects experimental optical measurements to the quantitative interpretation of blood samples.

The central measurement distinction is between a chemical species and a total signal. Oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin and methemoglobin can all contribute to measured absorbance, while functional oxygen saturation uses only the first two in its denominator. A fitted total optical signal therefore needs chemical interpretation before it becomes an oxygen-transport quantity.

An original synthetic example makes that separation concrete. If inferred concentrations are $H_O=8$, $H_D=2$ and $H_C=2$ with the remaining species absent, then functional oxygen saturation is $8/(8+2)=0.8$, whereas fractional oxyhemoglobin is $8/(8+2+2)=2/3$. Multiplying every concentration by two doubles the mixture's predicted absorbance at fixed path length under the Beer-Lambert law, but leaves both fractions unchanged.

Reference spectra thus help distinguish composition, concentration and denominator choice. This is the scientific role of the documented study; it should not be confused with directly measuring oxygen consumption, blood flow or cardiac output. Those quantities require additional observations and balance assumptions.