Lab & analytical techniques · Reference
What is LC-MS?
LC-MS couples liquid chromatography, which separates the components of a sample in solution, with mass spectrometry, which identifies and quantifies them by mass-to-charge ratio, combining separation and identification in one analysis.
How the two techniques are coupled
In LC-MS, a sample in solution first passes through a liquid chromatograph — typically HPLC — where its components separate as they move through the column at different rates. As each separated component leaves the column, it is delivered into a mass spectrometer. The challenge of the interface is to convert the liquid stream into gas-phase ions; this is usually done by electrospray ionisation, which sprays the eluent into a fine charged mist that releases ions gently enough to keep fragile molecules intact. The mass spectrometer then measures the mass-to-charge ratio of those ions.
Why combine them
Each technique alone has a limitation that the other addresses. Liquid chromatography separates complex mixtures well but, on its own, identifies components only by retention time, which is not unique.
Mass spectrometry identifies and quantifies molecules precisely but struggles with very complex mixtures fed in all at once. Coupling them means components arrive at the mass spectrometer one group at a time, already separated, so each can be characterised cleanly. The result is both separation and confident molecular identification in a single run.
Uses in research
LC-MS is a cornerstone of analytical work on substances that are too large, polar, or heat-sensitive for gas-phase methods, including peptides, proteins, drugs, and metabolites. It is central to proteomics, metabolomics, and pharmaceutical research. Its complementary partner for volatile compounds is GC-MS. Reproducible results depend on documented chromatographic and mass-spectrometric conditions and on calibration against reference standards.
Key facts
At a glance
- Couples: liquid chromatography with mass spectrometry
- Separation step: HPLC (components emerge at different times)
- Identification step: mass spectrometry (mass-to-charge ratio)
- Common interface: electrospray ionisation
- Suits: large, polar, or heat-sensitive molecules
- Key fields: proteomics, metabolomics, pharmaceutical analysis
Common questions
FAQ
What does LC-MS stand for?+
LC-MS stands for liquid chromatography–mass spectrometry. It combines a liquid chromatograph, which separates the components of a sample, with a mass spectrometer, which identifies and quantifies each component by its mass-to-charge ratio.
What is the difference between LC-MS and GC-MS?+
Both couple a separation step to mass spectrometry, but LC-MS separates components in a liquid and suits large, polar, or heat-sensitive molecules, whereas GC-MS separates components in the gas phase and suits volatile compounds that can be vaporised without decomposing.
The step most authors miss
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