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How does mass spectrometry identify and measure metabolites?

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Diagram illustrating metabolism with two sections: anabolic reaction on the left shows energy used to build larger molecules from smaller ones, while catabolic reaction on the right shows larger molecules breaking down into smaller molecules with energy released. — Metabolomics In anabolic reactions, a cell uses energy to combine small molecules into larger molecules. In catabolic reactions, molecules are broken down, and energy is released.

In the context of metabolomics, mass spectrometry (MS) is a powerful analytical technique used to identify and measure metabolites by sorting gaseous ions based on their mass-to-charge ratios.1

The Process of Identification and Measurement

The identification and quantification of metabolites typically involve the following steps:

Extraction and Ionization: Metabolites are first extracted from biological samples. Because the metabolome is chemically diverse, extraction protocols must be carefully chosen to recover various substances. Once introduced into the instrument, the molecules are converted into charged particles (ions) within an [ionization chamber].213
Separation: These ions are accelerated by an electric field and passed through a mass analyzer, which uses magnetic or electric fields to deflect the ions into trajectories dependent on their mass and charge.13
Detection: A detector records the intensity and mass of the ions that strike it, producing a mass spectrum. This spectrum displays the mass-to-charge ratio on the horizontal axis and ion abundance on the vertical axis.3

Approaches in Metabolomics

Targeted Metabolomics: This approach focuses on defined panels of biochemicals. It is highly sensitive, specific, and reproducible, often using heavy isotopes as labels to achieve precise quantification.4
Nontargeted Metabolomics: This method aims to provide a broad portrait of metabolism by measuring a large number of molecular variables. It is primarily used for discovery applications, such as comparing metabolites between different biological conditions.4

By analyzing the resulting mass spectra, researchers can identify specific biomarkers for disease detection and gain insights into complex metabolic pathways.53