Sulfhaemoglobin. Absorption spectrum, millimolar extinction coefficient at lambda = 620 nm, and interference with the determination of haemoglobin and of haemiglobincy anide.

The spectrophotometry properties of sulfhaemoglobin (SHb) and some derivatives were investigated using an improved technique for measuring the SHb fraction induced in human blood samples. The millimolar extinction coefficient of SHb at lambda = 620 nm was found to be 20.8 (S.D. 1.48; S.E. = 0.44; n = 11). In addition it was demonstrated that the spectral changes occurring in SHb containing haemoglobin solutions upon the addition of KCN, K3Fe(CN)6 and K3Fe(CN)6 +KCN invalidate the KCN addition method for the determination of haemiglobin. The influence of clinically occurring SHb fractions on the internationally standarized total haemoglobin determination were shown to be insignificant.