Molar absorptivities of human hemoglobin in the visible spectral range.

In a recent paper, Burkhard and Barnikol (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 52: 124-130, 1982) claimed that the absorption spectra of human (oxy-)hemoglobin are dependent on the total hemoglobin concentration (CHb) and it is suggested that this might also be the case with cyanmethemoglobin (HiCN). Such relationships would invalidate the widely used spectrophotometric methods for the determination of total hemoglobin and the fractions of various hemoglobin derivatives in human blood. Although Burkhard and Barnikol's findings are rather improbable considering earlier data, we measured the millimolar absorptivities of oxyhemoglobin (epsilon HbO2) and cyanmethemoglobin (epsilon HiCN) at various wavelengths over a wide range of concentrations (CHb approximately equal to 0.004-10 mmol x 1(-1)), using two different types of spectrophotometers. epsilon HbO2 and epsilon HiCN proved to be independent of CHb. Moreover the values obtained confirmed those in the earlier literature, whereas those of Burkhard and Barnikol are some 30% higher. Consequently there is no reason to doubt the validity of the generally accepted millimolar absorptivities of human hemoglobin.