Haemoglobin absorption spectra

Although the measurement of haemoglobin in whole blood is usually carried out by the haematology laboratory, the clinical chemistry laboratory may be asked to detect it in plasma, urine and faeces. In plasma and urine it can be identified by its characteristic absorption spectrum. It can also be detected in all three types of speciment by its peroxidase ability. Haemoglobin catalyses the reduction of hydrogen peroxide to water and at the same time a dye (e.g. guaiac) is oxidized to a coloured form. 

Haemoglobin containing an extra sulphur atom. It can be formed by the action of certain drugs, e.g. phenacetin, and can be detected by its characteristic absorption spectrum. 

Spectroscopic Method. This is the most certain and specific method of detecting carbon monoxide. The gas to be tested is passed into a dilute solution (i in 10, or i in 100) of blood which is then examined spectroscopically. Pure blood gives the spectrum of haemoglobin with its two absorption bands of which one is narrow and yellow, near the D line, while the other is less intense but wider in the green, near to the E line. Carboxyhaemoglobin also gives two bands in D and E but of equal width and intensity, somewhat closer together and also displaced towards the violet. 

Haems like in Scheme 1 are present within many proteins such as haemoglobin, myoglobin, and many other enzymes. The haem is essential for protein function and as proteins break down the haem material needs to be recycled/excreted. The haem also contributes to significant absorption in the 500-600 nm region of the spectrum and is often responsible for observed Q-bands. 

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