Cxlvii. Studies on Bile Pigments. Iii. the Quantitative Determination of Urobilin and Urobilinogen in Urine and Faeces

IN a previous paper [Naumann, 1936] the qualitative tests for urobilinogen and urobilin have been studied. In the following the quantitative aspect of the problem is treated. A basis for the estimation of urobilin and related compounds was first introduced by Terwen [1924; 1925]. The main features of this method consist in determining the sum of urobilinogen and urobilin as urobilinogen after reduction by means of a ferrous salt in alkaline solution, the extraction of the total chromogen with ether or light petroleum, the timing of the aldehyde reaction, the replacement of the hydrochloric acid by acetic acid by adding sodium acetate, and the comparison with a phenolphthalein standard in an Autenrieth colorimeter. The method has been examined and partly modified by Greppi [1926], Fuerth and Singer [1929], Heilmeyer [1931], Watson [1931], Royer [1934] and Christophe [1934]. Terwen's method is subject to the disadvantage of the non-specificity of the aldehyde reaction as explained formerly. Many of the interfering substances, e.g. indole and phenol derivatives, phenazone, Extr. Rhei etc., are extracted by ether and light petroleum; the replacement of the hydrochloric acid by acetic acid only partly eliminates this source of error. A further disturbance is caused by the presence of much bilirubin which is extracted partly by ether, whilst light petroleum does not extract bilirubin, but at the same time fails to extract urobilinogen completely. Also the final colour in the presence of interfering substances is more orange or brownish, which renders the colorimetric comparison rather difficult. EXPERIMENTAL.