title: Methemoglobin in blood as determined by double-wavelength spectrophotometry.
abstract: We describe spectrophotometric determination of methemoglobin (Met-Hb) in blood by absorbance differences at two wavelengths (characteristic of the instrument used) in the 500-600 nm region. Blood is diluted 100- to 200-fold with a solution containing KCN and carbon monoxide to convert hemoglobin to carboxyhemoglobin and Met-Hb to cyanomethemoglobin (CN-Met-Hb). Carboxyhemoglobin has the same absorbance at the two wavelengths used, so that the differences in absorbance reflect only the CN-Met-Hb component. After measurement of absorbance differences, potassium ferricyanide is added to convert all hemoglobin derivatives to CN-Met-Hb; samples are then remeasured at the same wavelengths. The percentage of Met-Hb is determined from the ratio of the absorbance differences. Results agree satisfactorily with currently accepted procedures and with calculated theoretical results for mixtures of oxyhemoglobin, carboxyhemoglobin, and Met-Hb.
mesh_terms: D002263:Carboxyhemoglobin / Q000032:analysis; D006801:Humans; D008706:Methemoglobin / Q000031:analogs & derivatives / Q000032:analysis*; D013053:Spectrophotometry; D013435:Sulfhemoglobin / Q000032:analysis
chemical_list: C007169:cyanomethemoglobin; D008706:Methemoglobin; D013435:Sulfhemoglobin; D002263:Carboxyhemoglobin