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 .