Three methods are given for the determination of organic nitrogen. The macro-kjeldahl method is described in B. The semi-micro-kjeldahl method is described in C. The block digestion and flow injection analysis is described in D. The major factor that influences the selection of a macro- or semi-micro-kjeldahl method is the concentration of organic nitrogen. The micro-kjeldahl method is applicable for samples containing either low or high concentrations of organic nitrogen but requires a relatively large sample volume for low concentrations. The semi-micro-kjeldahl method is applicable to samples containing high concentrations of organic nitrogen. This section is reprinted from the 20th Edition.