Studies on the determination of bile pigments. III. Standardization of the determination of urobilinogen as urobilinogen-aldehyde.

Severalpreparations of urobilinand stercobilinwere investigatedwith regardto their value as standardsfor the determinationof urobilinogenand urobilin in biologicspecimens.Productsof commercialoriginwere foundto be impureand thereforeunsuitablefor this purpose.Absorptivitieswere measuredfor solutions of the pigmentsin 3% FICI in methanoland for the chromogens, obtained by ferroushydroxidereduction,in the “quantitative”and “semiquantitative” methods for urobilinogen.Ascorbicacid was shownto be effective as a protectiveagent in filtrates from reductionmixtures. Spectraof urobilinogen-aldehyde, phenolsulfonphthalein, Pontacyldye mixture and phenolphthalein were compared. Phenolsulfonphthalein is recommendedas the artificialstandardof choice.The independence of thisprocedure frominstrumentalconsiderations, withinlimits,isdemonstrated withthe useof thisdye. COMMERCIAL UNAVAILABILITY of pure urobilin or stercobiin in the