Chromatography is a technique used to separate mixtures into their different components. Chromatography can be used to determine the type of oil used in paint or the type of resin used in a varnish.
In gas chromatography (GC), a solution containing a tiny sample of paint or varnish is injected into a stream of gas (usually helium) which is sent through a very fine heated column. The molecules in the sample separate according to their chemical and physical properties.
High performance liquid chromatography (HPLC) uses liquid to carry the sample through a column of porous material, causing the molecules in the sample to separate.
In both forms of chromatography, a mass spectrometer (MS) is often used to provide information on the separated components. This helps to identify which components are present in a mixture.