Elemental Analysis

Nitrogen Analysis & Techniques Used :

The method in use is an upgraded form of that originally researched in Switzerland and marketed by various firms in the US.  Fundamentally, the scheme involves combustion of a sample in ultra-pure oxygen at 990 deg C in a closed system. The products (gasses) are swept through copper to remove excess Oxygen and silver salts to remove halogens, phosphorus, and sulfur. Since the heat conductivity depends upon it’s composition, the mixture of remaining gasses is sensed.  The H2O is removed. Later the CO2 is removed and finally only N2 remains. Sensing is done after each removal.

The instrument is calibrated using various standards from the NIST.  Thus all three elements can be determined in one run from the same sample selection. Running one sample at a time enables us to check for inorganic residue post combustion.

Interferences are very few.  Very high fluorine levels (>60%) can cause high nitrogen results.  This can be circumvented. The optimal sample size depends upon theory. It is always best that the analyst knows all elements present (the molecular formula). If completely unknown, the operator will select about 2 mg for analysis. 

This equipment does well in the analysis of air-sensitive samples.  These samples are sealed under nitrogen (in a controlled atmosphere) in preweighed capsules.  After removal from the glove box, the capsule is reweighed and quickly inserted into the analyzer.  This “special handling” process can be done in less than 4 minutes thus minimizing any degradation of the sample.  There is a correction made for the increased nitrogen blank from the glove box gas.

The preceding is a brief description of the theory of operation for the CHN analysis system.  Please phone or e-mail if you have specific questions about your sample and this system.

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Established in 1956, Midwest Microlab, LLC, is equipped to provide rapid accurate organic microchemical analysis to research and industry. Specialties include analysis for Carbon, Hydrogen, Nitrogen, direct Oxygen, and halogens including Fluorine.