Abstract: This invention describes a method and apparatus for a liquid dispensing cartridge pump suitable for dispensing reagent in an automatic system. In embodiments, the present invention may include a liquid metering chamber that accurately controls the amount of fluid dispensed. In other embodiments, the amount of fluid may be controlled by the action of a diaphragm, which may be assembled into a cavity of a dispenser housing creating a metering chamber. In another embodiment, the volume created by the metering chamber determines the volume of dispensed fluid. When the diaphragm is compressed from its free or extended state to its inverted state, it may substantially conform to the inner surface of the metering chamber. The fluid enters the metering chamber through an upper unidirectional valve and exits the dispenser housing through a lower unidirectional valve.