A method and apparatus for capturing a chemical compound, typically an impurity, and for accumulating said chemical compound on a capture mass CAPT included in at least one removable adsorbent cartridge MC over a period exceeding 2 days, with a view to the external chemical analysis thereof. The apparatus ST suitable for capturing at least one chemical compound in a fluid flow for its detection and/or quantification comprise, downstream of said cartridge or cartridges, at least one device for measuring the cumulative flow which has traversed the cartridge or cartridges over a set time period. In a preferred variation of the invention, the capture mass CAPT is fragmented into a plurality of elementary masses CAPTi which allows for the spread of an irreversible adsorption front or the displacement of a chromatographic zone.