Instruments and Techniques
Exeter Analytical - Model CE 440 CHN Analyzer
Principles of Operation
The samples to be analyzed are weighed into consumable tin or aluminum capsules.
Mettler Toledo UMT2 balance
The resulting combustion products pass through specialized reagents to produce carbon dioxide (CO2), water (H2O) and Nitrogen (N2) and oxides of nitrogen. These reagents also remove other interferences including haloges, sulfur and phosphorus. The gases are then passed over copper to scrub excess oxygen and reduce oxides of nitrogen to elemental nitrogen. After scrubbing, the gases enter a mixing volume chamber to ensure a homogeneous mixture at constant temperature and pressure.
The mixture then passes through a series of high-precision thermal conductivity detectors, each conatining a pair of thermal conductivity cells
Between the first two cells is a water trap. The differential signal between the cells is proportional to the water concentration, which is a function of the amount of hydrogen in the original sample. Between the next two cells is a carbon dioxide trap for measuring carbon. Finally, nitrogen is measured against a helium reference.
Based on a 2.0 mg sample.
Source: Exeter Analytical, Inc.
Further readingCE-440 Theory of Operation
CHN Micro-Analysis: A Comparative Review of the Effects of Instrument Design on Analytical Performance