In the present invention, preparation of a sample for analysis of residual agricultural chemicals in a caffeine-containing food product such as tea includes a step in which residual agricultural chemicals are extracted from a food product using an organic water-soluble extraction solvent to obtain a liquid extract, a step in which a mixture of a treatment agent that includes a powdered basic carbon material–containing silica gel, the liquid extract, and an organic purifying solvent that can dissolve the residual agricultural chemicals is obtained, and a step in which some of the liquid content of the mixture is separated. The powdered basic carbon material–containing silica gel is normally prepared in accordance with a method which includes a step for causing gelling by adding hydrochloric acid to an aqueous solution of sodium silicate to which a carbon material has been added, and in which the quantity of hydrochloric acid added is controlled...

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