The Determination of Blood Ammonium by a Modification of the Conway Technic
WILLARD R. FAULKNER, Ph.D.
Department of Clinical Pathology
RICHARD C. BRITTON, M.D.
Department of General Surgery
SINCE the latter part of the nineteenth century the existence of ammonium in normal circulating blood has been questioned from time to time. Now it is generally agreed that minute amounts of certain substances do exist in the blood, which appear as gaseous ammonia after alkalization of the blood sample. This base is present in two forms: the ammonium ion, NH4+, and free ammonia, NH3. The relationship between the two forms may be represented by the equation
NH3 + H+ ⇌ NH4+
Because a proton is involved, the equilibrium is sensitive to pH and might be expected to shift greatly in pathologic conditions characterized by acidosis or alkalosis. Evidently this does not occur. According to Bessman,1 even at the extremes of physiologic pH variation more than 99.9 per cent of this base is in the form of the ion. Thus the term ammonium is preferable to ammonia, and will be used throughout this report to signify the summation of both forms.
Numerous methods for the quantitative estimation of ammonium in blood have been devised and have been presented in the chemical and medical literature.2–4 The accurate determination of the minute amounts of ammonium that exist in blood is difficult by any technic because of certain potential and subtle sources of error. The four principal sources of unreliability in all methods are: (1) minuteness of quantities of ammonium present in the blood; (2) ease of contamination of the specimen; (3) continuous increase of ammonium in blood after its withdrawal from the body; (4) alkaline hydrolysis of . . .