An analytical technique used to identify and supply information on the molecular structure of chemical compounds by ionizing its chemical species. The resulting molecular and fragment ions are detected and displayed on the basis of increasing mass/charge ratio (m/z) in a mass spectrum. When coupled with a gas chromatograph, a mass spectrometer can also be used to look for ions having particular characteristics such as biomarkers. Mass spectrometers are also used to determine stable isotopic ratios.