The analysis of nitrogen has been of great concern to various workers in the field of biology and chemistry, and a great deal of effort has been spent in the development of methods for it. Moreover, the analysis of nitrogen yields an indirect measure of the composition of such compounds as proteins. The classic analysis for nitrogen involves oxidation or reduction by digestive procedures. Such procedures are based on the original work of Johan Kjeldahl between 1883 and 1888. Kjeldahl employed in his initial investigations a digestive mixture of sulfuric and phosphoric acids to decompose many organic substances.' Essentially, the Kjeldahl procedure involves oxidation of organic matter, giving rise to carbon dioxide and water when boiled with concentrated sulfuric acid, the latter then being reduced to sulfur dioxide. The nitrogen present is converted to ammonium sulfate unless it was initially present as azo or nitro derivatives. In this case it is first treated with a mixture of salicylic acid and sulfuric acid, and the nitrated derivative thus formed is reduced with thiosulfate to an amino derivative. After complete destruction of the organic matter, an excess of sodium hydroxide is added to the sulfuric acid, and the liberated ammonia is distilled into a measured volume of a standard acid. Titration of the excess or residual acid with a standard alkali, using a suitable indicator, permits quantitation of the nitrogen content. Nitrogen also can be analyzed in organic compounds by conversion to ammonia followed by hypobromite oxidation of the ammonia to nitrogen. The nitrogen evolved is measured in gaseous form2 or quantitated via a mass spectrome ter. Many digestion mixtures have been proposed for use with the classic Kjeldahl method, and a host of additive aids to oxidation, metal catalysts, and substances to raise the boiling point have been suggested and employed. Some of these mixtures have very specific applications, and others are simply the result of a specific scientist's opinion that his mixture afforded superior digestive efficiency. The essence of the mechanism remains the same, however, regardless of the digestive mixture. Essentially, the Kjeldahl procedure consists of the introduction of a sample into a suitable flask with an appropriate digestive solution, the prolonged boiling of the organic matter to oxidize the carbon and hydrogen with reduction of the sulfuric acid to sulfur dioxide, and the subsequent reduction of the nitrogenous matter to a m m ~ n i a . ~ This procedure is both tedious and cumbersome; moreover, additional manipulative operations must be carried out in order to arrive a t a quantitative answer. The stumbling block in automating the nitrogen analysis of organic compounds on the basis of the principles established by Kjeldahl was the digestive phase. I t was necessary to provide a means for continuous introduction and removal of the digestive mixture and intermittent or continuous introduction of the material to be digested. A suitable time lag had to be provided so that