Why are heavy isotopes used in targeted metabolomics assays?

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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 targeted metabolomics, heavy isotopes are used to label substances to ensure that assays are reproducibly quantitative, highly sensitive, and specific.1

By incorporating these labeled compounds, researchers can employ the technique of isotope dilution. In this process, a known quantity of an isotopically enriched substance—often called a spike—is added to a biological sample. Because the heavy isotope acts as a tracer, it allows for the precise measurement of the mass and quantity of specific metabolites within a complex mixture. This method is particularly valuable in biochemistry for "tracing" the fate of compounds in metabolism and overcoming challenges where precise quantitative analysis by conventional means is difficult.234