Stability constants of haemoglobin cyanide and azide measured by two-wavelength spectrophotometric method.

A two-wavelength spectrophotometric procedure for the simultaneous determination of haemoglobin and haemoglobin cyanide (HiCN) (or of haemoglobin and haemoglobin azide (HiN3)) concentrations in mixtures has been developed and applied to the determination of the stability constants of HiCN and HiN3. The analytically reliable procedure allowed stability constants to be estimated with about 10% (relative standard deviation, coefficient of variation) uncertainty. Values of 1.9 X 10(6) and 2.0 X 10(5) 1 X mol-1 were obtained for HiCN and HiN3, respectively. These results are discussed in relation to the optimal composition of the reagents for blood haemoglobin assay by the two methods.