A Semimicro-Kjeldahl Method for the Determination of Total Nitrogen in Milk

Abstract

Recent research work in this laboratory pertaining to the nitrogen dis- tribution in dairy products made it desirable to develop a practical method for determining small amounts of nitrogen. A survey of the literature disclosed a number of methods designed for this purpose, but after careful consideration of the time factor, routine applicability and accuracy, the semimicro-Kjeldahl procedure used by Row- land (1) was chosen as the most practical method for the analysis of milk. Rowland does not describe the distillation apparatus he used, but stated that direct steam distillation was utilized to liberate ammonia from the digested samples. He used selenium oxychloride in the digestion mixture because it markedly reduced the time for digestion, increased the amounts of nitrogen determined and improved the agreement of duplicates. The results this author reported for the total nitrogen in milk are not compared with the Official Method (2), but he stated that duplicate deter- minations agreed within ___ 0.2 per cent nitrogen. The purpose of this experiment was threefold : (a) to design a semimicro- Kjeldahl apparatus, (b) to compare the efficiency of several digestion cata- lysts and (c) to compare both standard acid and boric acid as the ammonia receiving agents.