Abstract
A procedure is described for the determination of particulate organic nitrogen using Kjeldahl digestion in conjunction with measurement of ammonia by an indophenol-blue reaction. The method has a coefficient of variation of 1.5% at the 100-mcg nitrogen level. The detection limit is 3.5 mcg nitrogen. Beer's law is obeyed up to 100 mcg nitrogen. Quantitative recoveries of ammonia were obtained from glycine and glucosamine, but lower recoveries (77% to 87%) were obtained from arginine and histidine.