An Artifact in the Analysis of Oxygenated Blood for Its Low Carbon Monoxide Content

Abstract

Abstract A sensitive gas chromatographic method for blood CO determination was used to analyze samples of reduced and oxygenated blood having identical low CO content. Oxygenated blood always released more CO than did the reduced samples when neutral ferricyanide was used as oxidant. Several reagents for CO release from blood were applied to both oxygenated and reduced samples. CO release by K3Fe(CN)6 from oxygen-free blood or COHb solutions was complete and constant from pH 1.5 to 6. Values of extra CO released from oxygenated samples varied from 0.003 vol % at pH 1.5 to over 0.015 vol % at pH 6. The least amounts of excess CO were produced between pH 2 and 4.5. Neutral K2Cr2O7 causes less excess CO formation than does K3Fe(CN)6, but the rate of reaction with COHb is low. Neutral KMnO4 and acid K2Cr2O7 cause extreme formation of excess CO from blood in amounts many times the amount of COHb present. Acid KIO3 effectively releases CO from COHb solutions and reduced blood, but causes more excess CO formation from oxygenated blood than K3Fe(CN)6. When CO is released in citric acid with K3Fe(CN)6 at a pH of about 3.5, the CO released from oxygenated blood is only about 0.001 vol % greater than that released from reduced samples. These differences indicate formation of small amounts of CO during reactions used to release CO from blood. Reduced hemoglobin and carboxyhemoglobin appear to be much more stable to these procedures than is oxyhemoglobin.