Oxyhemoglobin method concentrations

Sims and Horn (S13) did not consider that the addition of urea to the sodium benzoate solution was of any advantage and observed speedy coupling at pH 6.0-7.0 without it. The addition of nitrite to the diazo blank was found to eliminate errors due to hemolysis, and colorimetric readings were made at 525 mp since this is the isobestic wavelength for oxyhemoglobin and methemoglobin. Urea-ethanol solution has also been used to facilitate rapid coupling of bilirubin with diazotized sulfanilic acid. Patterson et al. (PI) have been able to eliminate the cloudiness that tends to develop with this method by the addition of concentrated phenol. 

COHb is quite stable and its concentration does not change over a long period (up to 6 months) if the blood sample is stored in the dark and under sterile conditions. Blood levels of COHb are not expected to exceed 5% at ambient levels of CO. IPCS (1999) focuses on methods which can accurately measure COHb below 10%. A method which simply requires finger-prick blood is convenient for mass screening and is described in detail by Commins and Lawther (1965) in this method, the sample is diluted in ammonia solution, which is divided into two parts from one of these, CO is displaced by oxygen and the COHb containing part is placed in the sample beam of a spectrophotometer so that the instra-ment records the difference between the absorbance of COHb and oxyhemoglobin. 

The most important characteristic of oxyhemoglobin (Hb02) method is that it operates at low concentrations of molecular oxygen, which are physiological for a variety of cells. The great number of the reactions in which molecular oxygen participates is classified into three major groups (Keevil and Mason, 1978) ... 

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