Photometric studies on the diazo reaction for serum bilirubin.

Abstract

Photometric studies on the Malloy-Evelyn procedure for the determination of serum bilirubin have shown that the azobilirubin color intensity obtained when the diazo reagent acts for 30 min. upon a known amount of bilirubin added to serum in the form of the sodium salt is less than when the reaction takes place with the same amount of bilirubin in chloroform-alcohol solution. This suggests that the usual calibration curve prepared from bilirubin in chloroform-alcohol solution, when used as standard for serum bilirubin determinations, may give values which are about 10% less than the true bilirubin content of the serum. It has also been shown that with the 1 : 10 dilution of the Malloy-Evelyn procedure the azobilirubin from icteric sera does not obey Beer’s law beyond a serum bilirubin content of 15 mgm. per 100 ml. Evidence is submitted that the rate of azobilirubin color formation can be markedly accelerated by increasing the strength of the diazo reagent, and a new reagent is proposed by the use of which the time of color development can be reduced from 30 min. to 5 min.