The two techniques work particularly well together because many samples used in pharmaceutical research, biotechnology and life sciences contain several substances at once. Looking at the mixture as a whole can make it difficult to identify individual compounds. LC-MS provides a way of separating those components first and then examining them in much greater detail.
How does LC-MS work?
LC-MS consists of two stages, liquid chromatography (LC) and mass spectrometry (MS).
The liquid chromatography step is performed by passing a sample through a column with a liquid solvent. The column is packed with a material that interacts differently with the different compounds. On account of these interactions substances travel through the column at different rates and elute at different times. This is known as retention.
The compounds eluting from the chromatography column are directed to the mass spectrometer after separation. The molecules are ionised, or made into charged particles, so the instrument can measure them by mass-to-charge ratio.
This information may also then be used for the identification of the compounds from the original sample. This information will also provide quantitative information concerning concentrations.
What is LC-MS used for?
LC-MS applications are many. It is particularly useful when researchers need to look at compounds within complex biological or chemical samples.
In pharmaceutical research, LC-MS can be used to study potential drug candidates during drug discovery and development. It can be used by researchers to verify the identity and purity of compounds, to analyse the changes of a compound over time, or to study metabolites generated after a drug has been administered to a biological system.
It is also frequently used in pharmacokinetic studies. These studies look at what happens to a drug in the body, including absorption, distribution, metabolism and excretion. LC-MS is capable of identifying drug compounds and their metabolites in samples such as blood plasma, serum or urine.
Bioanalysis is another important application. Biological samples are complex and contain thousands of different molecules, so assessing a particular compound in them can be difficult. Many of these investigations require the sensitivity and selectivity that LC-MS can offer.
In addition to pharmaceutical research, LC-MS can be used in other fields, such as clinical research, environmental testing, food analysis, toxicology and metabolomics.
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Why is LC-MS useful in research?
One of the main advantages of LC-MS is the ability to extract detailed information from relatively complex samples.
Liquid chromatography enables the separation of compounds that could, otherwise, interfere with each other. Then mass spectrometry provides an additional layer of information by measuring the mass-to-charge ratio of the ions that emerge from those compounds.
This combination can help distinguish between substances with similar properties. Modern LC-MS instruments can also detect compounds at very low concentrations. However, the actual sensitivity depends on the instrument, the sample and the analytical method.
For researchers, this combination can be particularly useful when the amount of a compound available for analysis is limited.
LC-MS can also be adapted for different types of work. Some methods are designed mainly to identify unknown compounds, while others are developed to measure a specific substance accurately across a defined concentration range.
LC-MS in drug development
LC-MS Using a validated quantitative method, LC-MS can also measure at several points during the development of medicines.
This can help scientists confirm whether a newly made compound has the expected molecular properties at an early stage of their research. It can also be used to see if unwanted impurities are present.
As development progresses, LC-MS can also aid studies of drug behaviour in biological systems. For instance, researchers may need to measure the concentration of a drug in plasma at various points. The data obtained can be used to build up a picture of how quickly the compound enters and leaves the blood stream.
LC-MS can also be used to study drug metabolites. In the liver and other tissues, enzymes can chemically alter a medicine so that it produces metabolites with properties different from those of the original compound. Thus, the identification and quantification of these metabolites may form an important part of understanding the behaviour of a drug.
LC-MS and LC-MS/MS
You may also hear the name LC-MS/MS, which stands for liquid chromatography tandem mass spectrometry.
In LC-MS/MS the instrument does additional rounds of mass analysis. A selected ion can be isolated and fragmented (collision-induced dissociation or tandem MS) and the resulting smaller fragments analysed. The fragmentation pattern obtained can give more specific information on the compound being investigated.
LC-MS/MS is extensively used for sensitive and selective quantitative analysis especially in bioanalytical work. It is useful when a target compound has to be measured in a complex biological sample where other substances might otherwise interfere with the measurement.
LC-MS and LC-MS/MS are similar but are not interchangeable terms. LC-MS/MS refers specifically to a tandem mass spectrometry setup.
What samples can be analysed?
The type of sample used with LC-MS depends on the purpose of the study. Typical examples include blood, plasma, serum, urine, and tissue extracts. Researchers can also look at pharmaceutical formulations, chemical mixtures and samples from environmental or food studies.
Sample preparation is a significant part of the process. The sample could be made up of any of the following, among others: proteins, salts, and lipids. For this reason, based on the experiment being carried out, scientists might use filtration, extraction, dilution, or protein precipitation before introducing the sample into the LC-MS system.
The process of sample preparation could greatly influence the outcome of the experiment.
What does LC-MS analysis accomplish?
The information provided from LC-MS analysis may consist of the mass-to-charge ratio of the compound along with its retention time. In combination, these values can be used to identify compounds within a sample.
LC-MS can also allow for the quantification of the amount of a specific target compound with a validated method.
However, an LC-MS result does not automatically provide a complete answer. Interpretation depends on the analytical method, instrument settings, reference standards, sample preparation and other factors. Therefore, when using LC-MS data to support research or regulated work, it is critical to create and validate the method properly.
In summary
LC-MS is the pairing of the separation capacity of liquid chromatography with the molecular analysis of mass spectrometry. It is an ideal instrument for analysing compounds within complex samples.
LC-MS is a valuable technique in contemporary analytical and bio-analytical research, which includes everything from pharmaceutical compound identification to metabolite research and even the detection of drug levels in biological samples. The importance of LC-MS comes from its capability to make sensitive and accurate measurements, especially when scientists need not only to identify compounds in a sample but also to quantify them.
Research Use Only. This glossary explains terminology used in published research. It is not medical advice and does not describe any product for human or animal use.