Plasma haemoglobin determination using chlorpromazine as a non-carcinogenic reagent

Plasma haemoglobin was assayed with the non-carcinogenic reagent phenothiazine. This method is sensitive and allows the measurement of plasma haemoglobin concentrations in the range 4-500 mg/l with a within-run CV of 2.1%, and a between-run CV of 4.3%. A spectrophotometric scanning method (x) based on the determination of haemoglobin as haemiglobin cyanide using the Soret band at 419 nm correlated well with the phenothiazine method (y): y = 1.07x + 15.8, r = 0.995, n = 31. It was found that the absorbances in the phenothiazine method were markedly dependent on the concentration of phosphoric acid.