An improvement of the Folin method for the determination of urinary ammonia nitrogen

In the fall of 1907, during the progress of a metabolism research on “the influence of magnesium sulphate on metabolism,” 1 anomalous results were obtained in our quantitative determinations of urinary ammonia, whenever the magnesium salt was injected either subcutaneously or intravenously into the animal. 2 These anomalous results were found to be due to the facts that the magnesium was eliminated into the urines in question in relatively large quantities, as ammonio-magnesium phosphate and that the resultant deposits of crystalline triple phosphate were not thoroughly decomposed by sodium carbonate, as used in the Folin method, whereby ammonia, in variable amounts, remained in its solid form as triple phosphate in the urines under investigation. We, therefore, sought another method that would liberate all the ammonia from ammonio-magnesium phosphate without producing ammonia from such compounds as urea in the urine. None, however, was found that fulfilled both conditions. Consequently, we were obliged either to devise a new method, or else modify the Folin process, so as to make it liberate the ammonia from triple phosphate. We chose the latter course.