The determination of nitrogen in nitro, nitroso, and azo compounds by the direct application of Kieldahl's method leads to low results, particularly when the content of nitrogen attached to oxygen exceeds lOΒ°/o 1 . Many reagents have, therefore, been suggested for reduction of these types of nitrogen before the Kjeldahl digestion. The reduced nitrogen is then converted to ammonium sulphate from which ammonia is distilled and titrated.
It has been shown, however, that the distillation step in the Kjeldahl method can be eliminated advantageously. This can be achieved by employing either the formaldehyde reaction 2 or the determination of ammonia s with hypochlorite. Nitrogen has been determined by the latter method in organic compounds on the sub-micro 4, micro, semimicro 5 and macro scales and in agricultural and animal products 6.
Clearly, the possibility of determining nitrogen in nitro groups, etc., in organic compounds would make this method much more widely applicable. This required an investigation of the various reducing agents with a particular view to determining nitrogen eventually by the hypochlorite method. Some of the reductants successfully used in the usual Kjeldahl method are thiosalicylic acid ~, aromatic hydroxy compounds a, phenol and zinc dust 9, zinc in methanol and hydrochloric acid 10, zinc alone n, potassium persulphate and zinc dust la, stannous chloride ~a , sulphur 14, iron and aluminium 15. Hydriodic acid le and various carbohydratesl~, 18 have also been employed. Recent work in the field, particularly by BRADSTREET 18, indicates that sucrose brings about a quantitative reduction of oxygen-bound nitrogen in organic nitrogenous compounds.
We have shown that either glucose or zinc in methanol and hydrochloric acid is quite effective as a reductant and provides no interference in the later procedure. Glucose is particularly effective for the quantitative reduction of nitro, nitroso or azo groups in a large number of, compounds having different amounts of nitrogen.
EXPERIMENTAL
Reagents
All the reagents used were of analytical reagent grade.