ABSTRACT
Gas chromatography/mass spectroscopy (GC/MS) is probably the best technique to identify a wide array of unknown organic substances in sample matrices. The single-most important application of MS is of course to identify an unknown compound from its characteristic mass spectra. The interpretation of mass spectra requires some basic skill and knowledge of fragmentation of molecules. The number of Carbon atoms can be calculated from the relative intensities of the molecular ion peak, M and the isotope peak M + 1, which is one mass above the molecular ion. When an organic molecule contains N atom(s), its fragmentation pattern under electron impact ionization may be interpreted with some degree of accuracy by the nitrogen rule. The index of hydrogen deficiency (IHD) is used to calculate the number of rings and double bonds. In atmospheric pressure chemical ionization (APCI) sources, the CI occurs at much higher pressures. Organic substances that are not volatile are grouped under semivolatiles.
