A Note upon the Micro-Determination of Ammonia. ∗

Abstract

Several excellent procedures are available for the micro-estimation of ammonia of which the methods of Conway and Byrne 1 and Gibbs and Kirk 2 are notable examples. In connection with studies of tissue respiration it became desirable to determine quantities of ammonia of the order of 5 γ to 50 γ present in the Ringer fluid in which various tissues were suspended. Attempts were made to Nesslerize the de-proteinized fluid with measurement of the resulting light transmission with the Evelyn photoelectric colorimeter (Filter 440) as in the micro-non-protein nitrogen determination adapted for this instrument. 3 These were frustrated by immediate clouding of the Nessler-ized solutions as a result of the small amount of magnesium ion present in the Ringer fluid 4 employed. Inhibition of the precipitation was not obtained by addition of various stabilizers, e. g., gum ghatti, gum acacia, etc., although the onset and rate of clouding was slightly delayed by adding a small amount of 50% Rochelle salt solution prior to Nesslerization. This slight delay sufficed to make the photoelectric determination feasible. The following technic was found to yield moderately accurate results in spite of interfering magnesium salts.