DETERMINATION OF AMMONIA NITROGEN IN THE URINE OF SMALL RUMINANTS

The objective of the present work was to compare colorimetric and dist illation-titration methods to determine the ammonia-nitrogen (NH3-N) c oncentration in sheep and goat urine samples. Colorimetric methods use d were based on the indophenol reaction, whereas titrimetric methods w ere based on the alkali distillation of ammonia from the urine and its titrimetric determination with a standard acid. Colorimetric methods were only reliable when urine samples were diluted at least 1:20. Both colorimetric and alkali-distillation methods gave quantitative recove ries with standard NH3-N solutions, but when NH3-N was determined in u rine samples there was a significant discrepancy between analytical me thods on the measured concentrations. These were between 1.3 and 10-fo ld ton average 2.6-fold) higher with alkali distillation than with the colorimetric method. The difference between concentrations measured b y both analytical methods was significantly related (R-2 = 0.990; P < 0.001) to the concentration of urea in the urine samples. To study the effect of urea concentration, standard solutions containing variable concentrations of urea and NH3-N were prepared, and NH3-N concentratio n determined by both methods. Concentrations measured by colorimetry w ere similar to the actual concentrations irrespective of the urea conc entration of the solutions. In urea-free solutions, alkali-distillatio n methods gave values similar to the actual concentrations, but when u rea was present observed values were consistently higher than the expe cted concentrations. The overestimation increased with the urea concen tration of the solutions, with a significant (P < 0.001) relationship between both variables. Colorimetric methods were more reliable to mea sure NH3-N concentrations in urine samples containing high urea concen trations. (C) 1998 Society of Chemical Industry.