The gas chromatograph-mass spectrometer is a combination instrument used to separate the components of some mixtures. In the forensic laboratory the most common mixture contains drugs.
The gas chromatograph consists of an injector, a column in an oven, and a detector. The vaporised mixture is applied by the injector to the column. The column is a long (25m), thin (0.25mm) tube coated with an inert material to which the components of the mixture bind with varying degrees of tenacity. The oven is gradually heated to make the components leave the column in sequence. As the separated components leave the column the detector sends a signal to a computer which produces a graph of the detected components in the form of a series of peaks representing the quantity of component and the time that the component left the column.
Of course several compounds could be present in one peak, therefore the content of each peak passes to the mass spectrometer where they are bombarded with a stream of electrons that break up and ionise the molecules. This instrument separates the ions on the basis of their charge to mass ratio, and a graph of these can be produced for each peak from the GC.
