ABSTRACT
Principles Spectrophotometric analysis of haemoglobin is based on the fact that if a mixture of oxyhaemoglobin and deoxyhaemoglobin is read at two wavelengths, one at which there is a significant difference between oxy-and deoxyhaemoglobin, the other at the isobestic point of oxy-and deoxyhaemoglobin, the percentage saturation can be obtained. The difference in absorbance between oxygenated and deoxygenated haemoglobin is greatest at 625nm: 805nm is the isobestic point of oxyhaemoglobin and deoxyhaemoglobin where the molecular absorption coefficient is the same for both molecules.
