The Department of Chemistry and Biochemistry
The Michael Faraday Laboratories
Northern Illinois University
DeKalb, IL 60115-2862
CHN Elemental Analysis
The lab is equipped with a PerkinElmer 2400 Series II CHN Elemental Analyzer for the determination of carbon, hydrogen, and nitrogen content in organic and other types of materials, including solids, liquids, volatile, and viscous samples. The method is based on the combustion of the sample in an oxygen atmosphere at 925°C.
In CHN mode, the accuracy of this method is ±0.3%, so the sample needs to be very pure to pass.
This analytical service is also available to other interested institutions, academic or industrial. For information please contact Dr. Taesam Kim at firstname.lastname@example.org.
If you would like to have an elemental analysis performed, please provide a minimum of 3 mg of sample in a screw- or snap-cap vial (NO round bottom flasks!) and fill out the Elemental Analysis Request Form (PDF). Typically, 2 mg to 5 mg will be enough material for a duplicate run. In cases where you have very little sample available, it is possible to do one CHN run with as little as 1 mg for organic samples.
The determination of the mass percentage of CHN elements in the sample is based upon the direct weight of the material sampled. Therefore, it is very important that samples are dry, free of foreign substances such as solvent, dust, rust, hair, aluminum foil, parafilm, and paper filter fibers (the most common contaminant). The lab needs to know if and what metals, halides, or other interferences might be contained in the sample.
In CHN mode, the accuracy is ±0.3%. Samples must be very pure and have the correct chemical structure to pass elemental analysis. If there are any solvents or moisture trapped in the sample, the accuracy of the results will be affected. Also, if the sample is not homogeneous, duplicate runs will not agree to within ±0.3%.
If a sample is extremely volatile, it may lose mass due to evaporation after it has been weighed out, even if it is crimp-sealed in a special volatile sample pan. This can also cause the results to be inaccurate.
Some compounds are inherently difficult to combust completely. Incomplete combustion can also cause inaccurate results. In this case, the sample could be re-run under different conditions, with an added oxygen boost, or with the addition of a chemical combustion aid such as vanadium pentoxide.
As the calibration of the instrument requires the theoretical percentage of each element, it is important to have listed at least a range or approximate value of the percentage composition for each element in the compound.