Microanalysis Laboratory

School Affiliated departments and LAS


Instruments and Techniques

CHN
Exeter Analytical - Model CE 440 CHN Analyzer



photo Model CE 440 CHN Analyzer

Principles of Operation

The samples to be analyzed are weighed into consumable tin or aluminum capsules.

image of balance
Mettler Toledo UMT2 balance
image of sample
Sample
The capsule is injected into a high temperature (1000°C) furnace and combusted in pure oxygen under static conditions. At the end of the combustion period, a dynamic burst of oxygen is added to ensure total combustion of all inorganic and organic substances. If tin capsules are used for the sample container, an initial exothermic reaction occurs raising the temperature of combustion to over 1800°C.

CE-440 Flow Schematic Diagram

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.

ELEMENT RANGE DETECTION LIMIT ERROR
C 0-99% 0.10% 0.06%
H 0-85% 0.10% 0.06%
N 0-85% 0.10% 0.06%

Based on a 2.0 mg sample.

Source: Exeter Analytical, Inc.

Further reading

CE-440 Theory of Operation

CE-440 Specs

CHN Micro-Analysis: A Comparative Review of the Effects of Instrument Design on Analytical Performance

University of Illinois at Urbana-Champaign
Microanalysis Laboratory
47 Noyes Laboratory
MC-712 Box 36-1
505 South Mathews Ave.
Urbana, IL 61801
Kiran Subedi, PhD
Facility Supervisor

micro [at] scs [dot] illinois [dot] edu
tel: (217) 333-3095
8:30 a.m. — 5:00 p.m.
Monday through Friday

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