The spectrophotometric measurement of carboxyhemoglobin.

A simple, reliable and rapid method for the spectrophotometric determina­ tion of carboxyhemoglobin in fresh blood is described. A blood hemolysate is prepared by diluting a blood sample with 0.4 percent NH4 OH. Addition of sodium dithionite deoxygenates hemoglobin (and reduces methemoglobin if present) without affecting carboxyhemoglobin. Comparison of the 541/555 nm absorbance ratio for the hemolysate with the ratio obtained for solutions with known concentrations of carboxyhemoglobin serves as a means to determine the percent of carboxyhemoglobin present in the sample. Bilirubin and methemoglobin do not interfere with the procedure, and the standard curve is linear over the entire analytical range.