Tetramethylbenzidine--a substitute for benzidine in hemoglobin analysis.

Plasma hemoglobin is routinely measured by some modification of the benzidine-hydrogen peroxide method, particularly at low concentrations. Because benzidine is carcinogenic, and thus impractical for clinical use under current restrictions, the identification of a noncarcinogenic benzidine derivative has become important. 3,3',5,5'-tetramethylbenzidine fulfills this criterion, and consequently a method is described in this paper which uses it for hemoglobin determinations in the range of 1 to 100 mg/dl. Absorption spectra show this method to be far less influenced by plasma proteins and other substances than the benzidine method, and moreover the sensitivity of TMB is at least seven times that of benzidine under comparable conditions.