The non-protein nitrogen of blood

Abstract

In a previous publication, 1 the author described a modification of the method of Folin and Denis 2 for the determination of nonprotein nitrogen in blood. Trichloracetic acid was used to precipitate the protein and the trace that remained in the filtrate was removed by shaking with kaolin. It was shown that the nitrogen of an amino-acid mixture added to blood could be completely recovered by this method and that no nitrogen was split off from proteins by this treatment. Bock 3 recently described another method for obtaining protein-free filtrates from blood. He coagulated the protein by running the blood into boiling 0.01 N acetic acid, evaporated the filtrate to a small volume, precipitated most of the remaining protein with trichloracetic acid and removed the last traces with kaolin. It seemed that it should be possible to remove the protein from the filtrate from the coagulum by means of kaolin, directly, without the use of trichloracetic acid. This was found to be the case. Kaolin is added to the filtrate from the coagulum, shaking the mixture thoroughly, until the foam, which is at first voluminous and persistent, becomes scanty and comparatively evanescent. One drop of glacial acetic acid for each 100 c.c. of fluid is then added in order to agglutinate the kaolin and the mixture is then filtered. The filtrate is protein-free, so nearly as may be determined by the usual tests. It may be evaporated to small volume (less than one tenth that of the original blood) either at atmospheric or reduced pressure without foaming. Determinations of the nitrogen in such filtrates agree with those obtained by the trichloracetic acid-kaolin method. However, both methods are made inaccurate through the removal by the kaolin of nitrogenous substances other than protein