Gas chromatography mass spectroscopy Gas chromatography linked to mass spectroscopy (GC-MS) is an example of an instrumental method Different substances, carried by a gas, travel through a column packed with a solid material at different speeds, so that they become separated The number of peaks on the output of a gas chromatograph shows the number of compounds present The molecular mass is given by the molecular ion peak The position of the peaks on the output indicates the retention time A mass spectrometer can identify substances very quickly and accurately and can detect very small quantities Gas chromatography