Improved combustion techniques for the microdetermination of nitrogen in organic compounds with an automatic analyzer

Abstract

Routine analysis with the Coleman nitrogen analyzer, over the past 2 years, has led to various modifications in the procedure. It was found that compounds containing certain structures, such as 1,2,4-triazoles, pyridine rings, etc., often gave low results, while others containing long aliphatic chains gave high results. In many cases premature degradation of the sample, regardless of the melting point, has appeared to be the main problem. Cooling of the sample before and during the preheat period has eliminated this difficulty. The most effective catalyst found has been a mixture of silver oxide, manganese dioxide, vanadium pentoxide, and cobaltic oxide. This is placed on the sample which is weighed in a tin capsule. The use of tin capsules has proved to be more effective than aluminum boats with amine hydrochlorides and aliphatic chains. A modified post-treatment tube packing, with silver on aluminum oxide (alumina) between the copper oxide and copper, is used to effectively remove halogens and sulfur which quickly poison the copper packing. The modifications described have improved the reliability and accuracy of the instrument without increasing the time of a determination. The absolute deviation for standards was ±0.05% nitrogen, and for unknown compounds, ±0.14% nitrogen.