In the course of preliminary investigations in our laboratory on the use of the 15N isotope of nitrogen for metabolic studies it became apparent that the present method available for the separation of glutamine amide N and urea N (1) was inadequate for our studies. In this procedure, urea was hydrolyzed by urease, the urea N removed as ammonia by vacuum distillation at a pH above 10, and the glutamine amide N was then released by acid hydrolysis and removed as ammonia by vacuum distillation.
The above use of the technique of alkaline diffusion or distillation for the removal and determination of ammonia has been shown to cause alkaline hydrolysis of glutamine amide N (2-4). This problem of alkaline hydrolysis of glutamine amide N became quite apparent during the separation of labeled glutamine amide 15N and, unlabeled urea N by the above methods. Therefore, this investigation was designed to modify the above method in such a manner that urea N could be separated from glutamine amide N without isotopic cont,amination. EXPERIMENTAL Materials. n-Glutamine amide 15N, 95% enrichment, was obtained from Volk Radiochemical Company, Burbank, California. Urease, type II, 865 units/gm, was obtained from Sigma Chemical Company, St. Louis, Missouri. The Ionac C-101 resin was kindly supplied by Ionac Chemical Company, Birmingham, New Jersey. All other reagents were obt.ained from usual commercial sources.