Total nitrogen determination

As a preliminary to the consideration of automated, or more correctly mechanized, methods for the determination of total organic nitrogen the discussion of some general aspects of nitrogen determination is illuminating. There are at least four recent reviews, for example those by Bradstreet (1965), Fleck & Munro (I965), Jacobs (1965), and Munro & Fleck (1969), of the determination of nitrogen from which certain general principles for the estimation of nitrogen in samples of biological materials can be derived. An up-to-date review of analytical methods is incomplete without the mention of quality control. It is now apparent in the field of clinical biochemistry that continuous and daily checks of analytical precision and accuracy are essential for results to be reliable; the determination of nitrogen is no exception. The two principal methods of determining organic nitrogen were first described almost a century ago, the Kjeldahl method in 1883 and the Dumas method in 1831, yet it is only in recent years that important alterations in techniques have led to considerable improvements. The advent of gas-liquid chromatography was followed by considerable refinements in the Dumas method so that it is now possible to analyse dry solid samples rapidly, only a few minutes being required for each determination of nitrogen (see Fleck & Munro, 1965). The Kjeldahl method, however, remains the most widely used and convenient for samples of biological origin. The subsequent discussion relates only to the determination of the nitrogen content of samples of animal tissues, excreta and food. Substances such as keratin, horn, or soils may present difficulties and for such special applications it is essential to consult the recent reviews and to carry out careful recovery experiments with the technique adopted.