The invention provides a device for use in a cartridge for on-line preparation of a solution for a medical procedure. The device comprises a hollow body, the body having a first end and a second end and is provided with through holes in its wall. The second end is closed, while the first end is open and adapted for receiving fluid introduced into the cartridge. The fluid leaves the device through said holes. Furthermore, the invention relates to a cartridge provided with such a device, a method of manufacturing such a cartridge and the use of a charge of concentrate in such a cartridge.