Automated Simultaneous Determination of Ammonia and Total Amino Acids in Ruminal Fluid and In Vitro Media

Abstract

Catalyzed phenol-hypochlorite and ninhydrin colorimetric procedures were adapted to the Technicon AutoAnalyzer for simultaneous determination of NH3 and total amino acids in ruminal fluid or ruminal in vitro media. The manifold developed was compatible with a sampling rate of 40/h without significant sample-to-sample carryover. With proper storage, reagents for both the phenol-hypochlorite and the air-stable ninhydrin systems were stable for 8 mo. or more. Response of individual amino acids in the phenol-hypochlorite system were generally 1% or less than equimolar amounts of NH3. Certain amino acids inhibited NH3 color yield 10-15% when with equimolar amounts of NH3; the inhibitory effect of casein amino acids was only 2-3%. Although ninhydrin response, relative to leucine, of individual .alpha.-amino acids ranged from 62 (valine) to 151% (histidine), recoveries of casein amino acids from ruminal fluid had coefficients of variation of 1% or less. Coefficients of variation for NH3 recoveries from ruminal fluid by the phenol-hypochlorite procedure were about half of those for the Conway microdiffusion technique. Intraclass correlations for the adapted procedures indicated high degrees of accuracy and precision for both NH3 and amino acid analyses.