An Evaluation of the Use of Digitonin for the Analysis of Fæcal Sterols

Abstract

NUMEROUS reports have appeared in the literature dealing with the analysis of fæcal sterols^1–3. Before the complexity of the sterol mixture of fæces was appreciated⁴, a commonly employed procedure for the analysis of coprostanol was based on the difference between the total sterol determined by gravimetric analysis of the digitonide of the mixture and the amount of cholesterol or ‘chromogenic sterol’ calculated from the colour produced with the Liebermann–Burchard reagent^1,2. While many investigators recognize that the chromogenic property of coprostanol will introduce an error in the analysis if coprostanol is determined as cholesterol using the digitonide precipitation procedure, a more serious error arises from the fact that the digitonide of coprostanol is significantly soluble in many of the solvent mixtures used (for example, the Sperry–Webb determination for cholesterol⁵). This unusual solubility property of coprostanol digitonide was recognized early by Dam⁶ when he reported that in contrast to cholestanol digitonide, the digitonide of coprostanol was significantly soluble in methanol, a property which allowed the crude separation of the two sterols. This information prompted us to study the solubility of coprostanol digitonide in the solvent mixture routinely employed in the Sperry–Webb procedure and to compare our results with cholesterol digitonide as a reference.