Instrument-cartridge interfaces for fluidic analyzers that have an instrument and a removable cartridge are disclosed. For example, and in one illustrative embodiment, the instrument may include a needle that is adapted to penetrate a septum on a removable cartridge. In another illustrative embodiment, the instrument may include a plunger that is adapted to deform a deformable membrane on a removable cartridge. In yet another illustrative embodiment, the instrument may include a nozzle that is adapted to mate and seal with a flow channel on a removable cartridge. Techniques for detecting the flow rate in a flow channel on a removable cartridge, as well as the position of fluid in a flow channel of a removable cartridge, are also disclosed.