Determination of the carboxyhaemoglobin saturation of blood by spectrophotometric analysis.

The spectrophotometric method of Commins and Lawther (1965) for the determination of carboxyhaemoglobin saturation in blood was found to lead to systematic undervaluation, because of dissociation of the carboxyhaemoglobin, and physical dissolution of the carbon monoxide in the solvent used for the analysis. The theoretical relationship between the true and apparent carboxyhaemoglobin saturations was calculated and was found to be in satisfactory agreement with the experimental findings, using samples of blood saturated with carbon monoxide, and aerated solvent. The error is much smaller when using oxygenfree solvent, but it is nevertheless appreciable at high carboxyhaemoglobin saturations.