Principles of Liquid Chromatography - Mass Spectroscopy LC-MS

Liquid Chromatography-Mass Spectrometry (LC-MS) is an analytical chemistry laboratory technique for identification, quantitation and mass analysis of materials. This technique allows for the structural elucidation of unknown molecules through fragmentation. Similar to HPLC, LC/MS utilizes a compound's intrinsic affinity for both a "mobile phase" and a "stationary phase". Once the sample is in the solvent flow, it travels through an analytical column. The compounds present in the sample mixture are then separated depending on their affinity to the coated particles in the column. After the components in the sample are separated, they pass through a mass detector. Three ionization types are available for sample analysis, Electrospray Ionization (ESI), Atmospheric Pressure Chemical Ionization (APCI) and Atmospheric Pressure Photo Ionization (APPI). Both ESI and APCI are similar in that the ionization of the analyte(s) of interest occurs at atmospheric pressure. The differences between the two techniques lie in the way the analyte(s) of interest are ionized. The m/z analyzer (mass analyzer) is used to separate the ions according to their m/z ratio based on their characteristic behavior in electric and/or magnetic fields. More specifically, quadrupoles, quadrupole ion traps and time-of-flight (TOF) s have undergone numerous modifications and improvements over the past decade in order to be interfaced with ESI.