Liquid Chromatography-Mass Spectrometry

Analysis of pure solutions by mass spectrometry is typically done by direct infusion, however when the sample is composed of multiple components then an initial separation of those components is frequently useful and often essential. When some components of the sample interfere with MS analysis, such as inorganic salts and ionic buffers, these must be removed.

An extremely useful method of separating analytes, or of removing salts, is by chromatographic means. Typically HPLC or UPLC systems are used prior to mass spectrometric analysis and this is made easy by directly interfacing HPLC with MS, such that the output from the chromatographic column enters the MS directly.

LC-MS allows analytes from a mixture to be analysed by MS individually, thereby considerably simplifying data interpretation.

Separation of complex mixtures prior to MS analysis is typically carried out by reversed phase chromatography, which uses hydrophobic interactions of the analyte molecules with carbon chains attached to chromatographic resin. This process also effectively removes ionic species, such as the salts and buffers that are typically used in life science applications and which interfere with MS measurements.

Interfacing liquid chromatography to MS is straightforward. Our mass spectrometers are interfaced to Dionex Ultimate systems and allow optimal flow rates of either 100-500 microlitres per min, or 0.3-10 microlitres per minute, depending on the application. This allows mass measurements of multiple analytes present in a mixture in a single experiment.

LC-MS can be used for a diverse range of sample types and applications, ranging from analysis of potential drug compounds, analysis of molecules present in urine, mass measurements of proteins contained in buffer systems or analysis of small hydrophillic metabolites.

LC-MS is often preferred to direct infusion MS for the analysis of unknowns, since the automatic removal of ionic species aids MS detection of other, non-ionic species.

LC-MS is highly sensitive and sample amounts are typically measured in the microgram range or lower. If samples are already in solution, then low micromolar concentrations, or less, are required.