Quantification of small amounts of hemoglobin in polyacrylamide gels with benzidine.

Benzidine-hydrogen peroxide is a sensitive blood stain. Since benzidine is carcinogenic, less hazardous substitutes have been sought which retain the specificity and sensitivity of benzidine. We have tested two benzidine derivatives, 3,3′-dimethoxybenzidine and 3,3′, 5,5′-tetramethylbenzidine, reported to be satisfactory substitutes, but have found both to be unsatisfactory for quantifying small amounts of hemoglobin (Hb) on polyacrylamide gels. However, our data show that benzidine stains gels with an intensity proportional to the amount of Hb present when the staining time and temperature are controlled. The stain is fast, sensitive, and specific for Hb, gives very little background stain, and is stable if the gels are thoroughly rinsed and stored in distilled-deionized water. The relative amounts of Hb in different bands or different gels may be quantified later by densitometry. Procedures are suggested for using benzidine while giving adequate attention to governing regulations and personnel safety.