There are many different techniques used to analyze the progress of a reaction. Most commonly, as it is cheap, available, and effective, thin-layer chromatography (TLC) is the method of choice. However, many chemistry researchers often employ an additional technique in order to corroborate the results of TLC as well as to increase their certainty of having obtained a particular product. This technique is called gas chromatography-mass spectrometry (GC-MS).

GC-MS combines the principles of gas/liquid chromatography with mass spectrometry such that it allows for the identification of various chemical substances within a single sample – exactly what is needed for characterization of a chemical reaction – but with more acuity than simply by TLC. And, of course, there is the added benefit of obtaining mass spectrometry data for the sample at the same time.

The GC part of the GC-MS is a capillary column that, like column chromatography, uses chemical properties that allow separation of different chemicals in the reaction solution as it travels with an inactive solvent. As the chemicals elute, they are then shuttled into a mass spectrometer. In the MS, the molecule are bombarded with high energy electrons that fragment the molecule into little pieces. They are then accelerated through a magnetic field and fragments of different mass/charge (m/z) ratios will hit the detector at different points, allowing for differentiation. As charge is typically 1, m/z approximates mass very well.

A sample GC-MS spectrum might look like this (top – GC, bottom – MS):

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