To state the obvious, researching metabolomics is complex! As a still relatively new branch of ‘omics’ researching and understanding the metabolism of living organisms in a wide range of conditions, including in health and disease, offers up complex matrices, large numbers of analytes to map and low levels of detection required; plus the sheer amount of data involved. There is no doubt advances in mass spectrometry, particularly high-resolution accurate mass instruments, have helped shape the study of metabolites allowing sensitivity in the femtomolar and attomolar levels.
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Most research scientists will be familiar with liquid chromatography methods to separate out compounds of interest then hyphenating these techniques to a mass spectrometer to harness the additional resolving power and sensitivity required. Gas chromatography is another tool in metabolomics profiling, although not many metabolites are truly volatile, derivatization can be used to detect, for example, amino acids using GC-MS, however, derivatization comes with its own issues as detailed in my previous blog post. LC-MS would be the overarching technique with many citations in the literature. However, LC-MS does also have some limitations in its capabilities.
This diagram demonstrates the analyte areas generally covered using HILIC or reverse-phase liquid chromatography in terms of polarity and ionic properties.
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Any analyte which is highly polar and highly ionic, such as sugar-phosphate isomers or those in the TCA (tricarboxylic acid) cycle, such as citrate, isocitrate, malate, and glutamate, are better suited to ion chromatography. Couple this to mass spectrometry and you have separation designed for these compounds with all the sensitivity and resolving power of a mass spectrometer.
Ion Chromatography coupled to mass spectrometry is a growing technology in many fields due to the fact it can fill in the gaps left by LC-MS analysis. IC-MS is used in targeted and untargeted metabolomic profiling. Analyzing small polar metabolites has been a key part of research into metabolic disturbances in oral cancers. Methods have been developed to analyze mono and diphosphate sugars in under nine minutes. With the advances in HRAM MS systems, you can calculate the empirical formula of the target compound from the molecular ion. If you have gaps in your metabolomics profiling, can IC-MS help you reach further?
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