I am studying haemoglobin absorption spectra in its oxygenated and deoxygenated state and I compiled values from different sources including:
A PhD thesis by van Assendelft [1], using extinction coefficients in (mmol/L)-1/cm
A book compiling almost one century of research on the topic by the same laboratory that helped standardizing the haemoglobin cyanide standard [2]. Extinction coefficients in the same unit as [1], numerical values are very close.
Coefficients compiled by Scott Prahl[3]. The unit is the same but there is a factor 3.7 up to 4.0 between his data and that of Assendelft and Zijlstra.
Coefficients measured by Kolyva[4].
All the published coefficients are defined as base 10 extinction coefficient. That is if I is the light intensity, they are expressed in Beer-Lambert law as:
$I = I_0 \cdot 10^{-c\cdot \varepsilon \cdot l}$
Where $l$ is the light path length (cm), $c$ the concentration in absorbing compound (mol/L) and $\varepsilon$ the molar extinction coefficient (L/mol/cm).
How comes there is a 3.7-4.0 factor between Prahl and Kolyva data on the one hand and Assendelft and Zijlstra on the other hand?
At first I thought of some $log(10)\approx2.3$ difference, as if some of the author forgot to precise that they used base $e$ extinction coefficient at some point but it does not fit. If anyone has an idea on the topic, the help would be most appreciated.
Further information
The cyanmethaemoglobin method is often used for the determination of the haemoglobin concentration of a solution. In particular, its absorbance at 540nm is known to be 11.00L/mmol/cm[5] which is in agreement with Assendelft and Zijlstra published data.
References
- O.W. Assendelft, Spectrophotometry of Haemoglobin Derivatives, 1970. ISBN: 902320560X.
- W.G. Zijlstra, A. Buursma and O.W. van Assendelft, Visible and Near Infrared Absorption Spectra of Human and Animal Haemoglobin, 2000. ISBN: 9067643173.
- Scott Prahl, Optical Absorption of Hemoglobin, 1999, https://omlc.org/spectra/hemoglobin/
- C. Kolyva, Systematic investigation of changes in oxidized cerebral cytochrome c oxidase concentration during frontal lobe activation in healthy adults, 2012. DOI: 10.1364/BOE.3.002550. Coefficients are in MEDIA 1.
- F. Meng, Determination of extinction coefficients of human hemoglobin in various redox states, 2017. DOI: 10.1016/j.ab.2017.01.002. Table 1.