Analyzing a solid sample for carbon, nitrogen and hydrogen can tell researchers a good deal about their material. Whether you are an ecologist looking at the C:N ratio of a foliage sample, or a chemical engineer ensuring that your synthesis produced material with the correct amount of carbon you were expecting, this device gives you the ability to measure the masses and ratios of carbon, nitrogen and hydrogen without digesting the materials and diluting them. In essence, the Costech ECS 4010 is a specialized gas chromatograph (GC), set up for detecting permanent gasses and measuring them via specific reactions and a Thermal Conductivity Detector (TCD). The chromatography management software allows the researcher to set up a calibration curve and large set of unknowns and allow the system to do the work with minimal supervision.
Prior to analysis, solid samples are wrapped in a tin foil capsules. The autosampler deposits these samples into an oxygen rich combustion zone, where the contents of the capsule combust and a specific set of catalysts ensure that all carbon in the sample forms carbon dioxide and that nitrogen is converted to N2 gas. In the next reaction vessel reduced copper wire scavenges all of the remaining oxygen. All hydrogen in the sealed and oxygen enriched, combustion chamber will naturally form water with no additional catalyst required. The gas products of this combustion then migrate through a large bore separation column (2 to 3 m in length) to separate the gasses, then to the TCD where it travels through a channel parallel to a stream of helium reference gas, which is also doubles as the carrier.
If a shorter analysis is desired, a water trap can be inserted just prior to separation, cutting the analysis time by more than half, removing the ability to measure hydrogen, but still giving accurate carbon and nitrogen values.
Additionally, the combustion chamber can be changed and a large capacity water trap installed, so that sulfur can be analyzed, converted by catalyst to sulfur dioxide. The nitrogen and carbon are treated as they are in CHN mode. In this configuration, water vapor must be removed so that sulfuric acid does not condense on the surface of the metal columns, but carbon and nitrogen can be analyzed as well, albeit with reduced efficiency.
We can also change the method of sample decomposition from combustion to pyrolysis and perform oxygen analysis on solid samples using the same TCD but with a different set of catalysts and a different, oxygen selective column.
However, even in CN mode, this system is not one that researchers can generally “jump into.” Some method development will be required to ensure that you have an adequate amount of nitrogen to get a signal, 0.007 mg at a minimum, but not so much material that you have too much carbon for the detector. We try to keep carbon below 5 mg per sample. Similar, test runs will have to be performed for other modes before large scale testing on your materials can begin.
CEST has two of these devices, one dedicated in “macro” mode, so that larger samples with poor carbon and nitrogen content can still be measured. For this system, samples sizes up to 70 mg can be combusted and measured, but the same limitations for carbon content exist.