Metabolomics [1] is a newly emerging field of 'omics' research. The metabolome [2] is defined as the complete set of small molecule endogenous metabolites, intermediates and metabolism products found in an organism. It can provide an instantaneous snapshot of the entire physiology of a living being. With its potential to provide a comprehensive snapshot of the biochemistry of a biological system, metabolomics can be used for life science research in areas such as disease and biomarker discovery. Metabolomics can also be combined with genomics, transcriptomics and proteomics studies, which are also known as multi-omics, to provide comprehensive insights into biological processes.
In general, metabolomics refers to metabolite profiling or the differential study of the metabolome between experimental and control groups when challenged with an external stimulus such as a drug treatment, a biochemical or environmental stress, or pathologies such as mutant/resistance-bred organisms. The stimulus could also be non-biological, such as food processing; as a consequence, metabolomics has huge potential across several application areas, including food and nutrition.
Because metabolomics aims to comprehensively identify and measure a large number of compounds in complex mixtures, its goals are a challenge for standard analytical chemistry. As a result, mass spectrometry has emerged as an alternative to NMR-based metabolomics, offers high selectivity and sensitivity, and has the potential to assess metabolites in both a qualitative and quantitative manner.
For scientists without specialized training in the field of mass spectrometry, using this approach can feel daunting. There are four fundamental areas one must master in order to be successful in metabolomics:
As endogenous metabolites are diverse in their physico-chemical properties, as well as varying in abundance, a true comprehensive metabolomics study will require orthogonal sample preparation and separation techniques. In reality, most experiments are not comprehensive and there is a bias towards certain classes of compounds.
The mass spectrometer can also introduce bias into the study. Utilizing positive or negative ion mode can affect which compounds can be ionized and detected.
Liquid chromatography (LC)-MS offers the broadest coverage of compounds due to its ability to work with different column chemistries. Common LC-MS compounds include lipids, polyamines, alcohols etc.
Samples that are volatile and amenable to chemical derivatization are well suited for gas chromatography (GC)-MS. Also GC offers high resolving power and a low cost-per-sample.
Ion chromatography (IC)-MS is best suited to charged or very polar metabolites that are difficult to analyze by LC-MS, including metabolites such as sugar phosphates and amino acids. IC also offers high resolution, enabling separation of isomers for mass spectrometry analysis.
