Method for extracting low-molecular-weight substance existing in biological sample

A method for extracting a low-molecular-weight substance existing in a biological sample from the sample, the method comprising:

• 1) an adsorption step of adsorbing the low-molecular-weight substance on porous carbon by mixing the biological sample with the porous carbon having mesopores of 3.5 nm to 150 nm and micropores of a larger size as a hierarchical structure, and then recovering the porous carbon from the obtained mixture, or by bringing the biological sample into contact with a filtration filter on which the porous carbon having mesopores of 3.5 nm to 150 nm and micropores of a larger size as a hierarchical structure is disposed or supported;
• and
• 2) a releasing step of releasing the low-molecular-weight substance from the porous carbon by mixing the porous carbon having the low-molecular-weight substance adsorbed thereon, obtained after the adsorption step, with an aqueous solution containing 0.1 mass % to 1 mass % of spherical silica having an average particle diameter of 10 nm to 100 nm and containing 10% to 12% of acetonitrile, or by causing the filtration filter obtained after the adsorption step to contact and pass through the aqueous solution.