A Stable "bilirubin" Standard.

mamiy serum samples has intensified our need for stable bilirubin standards for routine, repetitive calibration purposes. Crystalline I)ilirubin serves as a suitable primary standard, and when dissolved in chloroform, it yields reasonably stable stock solutions. However, whemi this is diluted with methanol to prepare a working standard, the resultimig solution lacks adequate stability for routine daily use. Similarly, when i)ilirul)nl is dissolved iii dilute alkali and quickly diluted with albumin solutions, the workimig standards are not as stable as one might desire. Some authors have suggested the use of pooled serum specimens or of commercial quality control sera, but these are neither as convenient nor as economical as omie might like. In seeking a solution to this prosaic but practical problem, we have sought a jure, stable, commercially available aromatic amine (or related material) which -oul(l couple with diazotized sulfanilic acid under the appropriate reaction comiditions to yield a chromogemi with spectral qualities similar to those of azobilirubin. Such a mnat.erial, N-(1-naphthyi) ethylenediamine dihydrochioride, has been foumid, and its applicability as a simulated biiirubin standard has been proecl during the past 18 months of daily routme USC.