Gas Chromatography-Mass Spectrometry (GC-MS).
It permits separation of a complex mixture into its components, before ionization and mass analysis. This is particularly useful when analysing relatively low levels of target compound derived from complex biological mixtures. The target analyte must to relatively volatile or must be susceptible to conversion into a volatile derivative to permit GC separation. In general, the Derivatized analyte should have a MW of less than 1000 Da, although Derivatized analytes with MW upto 1000-2000 Da can also be analysed. EI can CI in positive and negative modes are employed for ionization.