Liquid chromatography–mass spectrometry

Liquid chromatography -mass spectrometry (LC / MS, HPLC -MS) is a biochemical process for the separation and determination of molecules by a combination of liquid chromatography (LC or HPLC) with mass spectrometry (MS). The chromatography for the separation of molecules in a mixture, and the subsequent mass spectrometry is used for identification and / or quantification of substances. In general, more detectors be interconnected such as UV, ELS or conductivity detectors in LC yet.

Principle

One of the great difficulties in the LC / MS was the interface between the long Chromatographieteil and the mass spectrometer. At this point, excess sample volumes and in particular the solvent must be removed. Usually about 90 % of the solution is removed from the chromatography and the residual material is vaporized with different gas streams. While early devices had frequent defects and contamination of the interface, there are now devices that are suitable for routine use in the analytical laboratory.

As ionization today are electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI ) are used. Another way to circumvent the problems associated with these methods, the reduction of the sample volume in a nano-LC/MS. Here, the chromatographic separation with a much lower flow rate is performed, usually between 200 and 1000 nL / min. This eliminates the need for a carrier gas, which spills occur less frequently. A nano -LC unit a whole is more susceptible to other interference such as clogging of the column.

Through the coupling as a result of the methods is, for each point of the chromatogram is a mass spectrum is available. This enables the chemical structure of impurities in mixtures inform and present as an impurity profiles. The standing by the large number of mass spectra available information or data set provides workstation still facing challenges. Great effort is straight at the LC / MS analysis of proteins therefore operated, filter out false positive results. Since different LC / MS instruments ( and coupling methods ) often do not give comparable mass spectra, a spectrum interpretation on spectral databases (such as in gas chromatography -mass spectrometry (GC / MS) usual) is very restricted. Therefore, the elucidation of the chemical structure with LC / MS requires a high degree of experience and a comprehensive knowledge of the possible fragment masses. The use of MSxMS - coupling through triple-quad or ion trap devices therefore often aims to gain further information on the substances to be tested. The interpretation of the LC / MS measurements can also be supported by liquid chromatography / nuclear magnetic resonance spectroscopy measurements (LC / NMR).