Die Bestimmung von Zentimilligrammengen Stickstoff in organischen Substanzen

To determine the nitrogen content of a material, about 0,3 to 0,8 mg is mineralized with sulfuric acid in a quartz tube that is fused shut. The reaction products (sulfuric acid and ammonium sulfate) are percolated over an anion exchanger in hydroxide form. The resulting ammonium hydroxide is titrated with diluted perchloric acid and the endpoint determined with a Ph-meter. The lower limit of the suggested procedure is around 30μg nitrogen. The accuracy is better than 0,25 % absolute. Only metals interfere with the determination.