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Why is it difficult to extract both lactic acid and squalene from the same biological sample?

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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 field of metabolomics, the difficulty in extracting both lactic acid and squalene from the same biological sample stems from the extreme chemical diversity of the metabolome.1

These two substances possess vastly different physical and chemical properties:
* Lactic acid is a highly hydrophilic (water-loving) substance.1
* Squalene is an oily, hydrophobic hydrocarbon.12

Because a compound is most soluble in a solvent that it closely resembles structurally, a single extraction protocol is rarely efficient for both. A solvent system optimized to recover highly hydrophilic molecules like lactic acid will typically perform poorly when attempting to extract oily, lipophilic molecules like squalene. Consequently, metabolomics researchers must often navigate these challenges by developing specialized assays, as there is no universal standard for extracting such chemically diverse metabolites simultaneously.31