Liquid Chromatography - Mass Spectrometry (LC-MS)
Liquid chromatography mass spectrometry (LC-MS) is an analytical chemistry laboratory technique for identification, quantitation and mass analysis of materials.
Similar to HPLC/UPLC, a pump is used to provide a continuous flow of a solvent into which a dissolved sample is introduced. Analytes within the dissolved sample are then separated based upon their intrinsic affinities for both a “mobile phase” (typically a buffered solvent) and a “stationary phase” (porous solid support with specialized coating). After the analytes in the sample dilution are separated, they pass through a UV detector and into a mass detector.
The mass detector can be equipped with probes to perform either atmospheric pressure chemical ionization (APCI) or electrospray ionization (ESI). Both APCI and ESI are similar in that the ionization of the analyte(s) of interest occurs at atmospheric pressure. APCI is more effective than ESI with non-polar species in specialized circumstances, as the collisions with the reactive gas may provide the molecule with a charge ([M+H]+ ions).
For common circumstances, ESI nebulizes the sample producing ions that are either positively or negatively charged. Minimal (or no) fragmentation occurs, allowing for determination of the molecule’s molecular weight.
Once the parent ions are produced, they may be trapped using an ion trap (IT) and subjected to further fragmentation experiments, the number of which depends on the concentration of the analyte. For each experiment, fragment ions specific to the parent ion are be observed and can provide valuable information about the compound of interest.
As an additional option, EAG can perform LC tandem MS (LC-MS-MS) experiments with customized method development. Instead of being trapped using an ion trap as discussed above, ions migrate through a series of mass analyzers undergoing exclusion and fragmentation (also referred to as MS2) for highly sensitive and selective mass analysis using a triple quadrupole mass spectrometer.
For both UV and MS responses, the measured peak area or height is concentration-dependent and may be used to quantify the component.