The present invention relates to a device, to a system, and to a method for the preparation and fractioned dispensing of samples of a fluid. The device of the invention comprises a body having formed therein guide means suitable for receiving a sample-taker member and for guiding it in translation through the device, and at least one preparation chamber enabling an aliquot of a fluid sample dispensed into the chamber by a said sample-taker member to be prepared in a stream of a suitable reagent. The guide means pass through the preparation chamber and communicate therewith to enable an aliquot of fluid to be dispensed into the chamber in a determined position of the sample-taker member in the guide means. The preparation chamber has an introduction orifice for introducing at least one reagent into the chamber for mixing the reagent with an aliquot, and at least one dispensing orifice for dispensing the mixture formed by said aliquot and said reagent to recovery and/or analysis means.