One such detector, known as a flame ionization detector (FID) analyzes the separated components from the GC by combusting them and analyzing the spectrum of said combustion. Each chemical compound exhibits a unique spectrum when combusted,
This unique spectrum is because, withIn quantum theory, electrons returning to their rest state after having energy added to them (such as being heated) give off a characteristic frequency tied to the properties of the atom to which they are attached. For example, the salts of copper give off a characteristic green color even to the naked eye. A flame ionization detector can test the atoms in a very small sample and record the frequencies, which can then be compared to standard samples to identify all the compounds in the sample.
It should be noted that a flame ionization detector is not the only detector which can be used in conjunction with gas chromatography, and many other detectors exists for specified applications. Gas chromatography can further be used in conjunction with mass spectrometry (a process known as GC/MS) to accurately discern the composition of the sample by means of analyzing the mass of the components of the sample.
In medicine, gas chromatography is used to test for toxins in the blood and hair, and is even sensitive enough to test a single hair for compounds deposited in it as it grows. It can easily detect quantities of compounds that are too small to test for with standard chemical tests. It can also be used on just about any type of tissue.
However, gas chromatography is very expensive. Only the best hospitals and labs are typically equipped with the necessary equipment.