A method of performing a measurement on a sample containing an analyte using a cartridge, wherein the cartridge comprises: - a first reservoir at least partially filled with a reagent fluid; - a second reservoir at least partially filled with particles; - a pumping chamber, wherein the pumping chamber is formed from a cavity, wherein the cartridge further comprises a plunger mounted within the pumping chamber, wherein the plunger is configured for changing the volume of the pumping chamber, wherein a single expansion of the pumping chamber causes transport of both reagent fluid and particles into the pumping chamber; - at least one first pumping chamber conduit (120, 120') connecting the first reservoir and the pumping chamber; - at least one second pumping chamber conduit (122, 122') connecting the second reservoir and the pumping chamber; - an outlet for dispensing the reagent fluid and the particles from the cartridge; - an outlet conduit connecting the outlet to the pumping chamber; and - a valve for sealing the outlet conduit; wherein the method comprises the steps of: • closing the valve; • applying a force to the plunger to transport a first defined volume of reagent fluid and a second defined volume of particles into the pumping chamber to form a mixture of reagent fluid and particles, wherein applying the force to transport the first defined volume of reagent fluid and the second defined volume of particles into the pumping chamber to form the mixture of reagent fluid and particles comprises expanding the volume of the pumping chamber with the plunger; • opening the valve; • forcing the mixture in the pumping chamber using the plunger to dispense the mixture from the outlet into a fluid receptacle for mixing with the sample containing an analyte, wherein forcing the mixture in the pumping chamber to dispense the mixture comprises reducing the volume of the pumping chamber with the plunger; and • performing the measurement on the sample containing an analyte using an analytical unit. - a first reservoir at least partially filled with a reagent fluid; - a second reservoir at least partially filled with particles; - a pumping chamber, wherein the pumping chamber is formed from a cavity, wherein the cartridge further comprises a plunger mounted within the pumping chamber, wherein the plunger is configured for changing the volume of the pumping chamber, wherein a single expansion of the pumping chamber causes transport of both reagent fluid and particles into the pumping chamber; - at least one first pumping chamber conduit (120, 120') connecting the first reservoir and the pumping chamber; - at least one second pumping chamber conduit (122, 122') connecting the second reservoir and the pumping chamber; - an outlet for dispensing the reagent fluid and the particles from the cartridge; - an outlet conduit connecting the outlet to the pumping chamber; and - a valve for sealing the outlet conduit; • closing the valve; • applying a force to the plunger to transport a first defined volume of reagent fluid and a second defined volume of particles into the pumping chamber to form a mixture of reagent fluid and particles, wherein applying the force to transport the first defined volume of reagent fluid and the second defined volume of particles into the pumping chamber to form the mixture of reagent fluid and particles comprises expanding the volume of the pumping chamber with the plunger; • opening the valve; • forcing the mixture in the pumping chamber using the plunger to dispense the mixture from the outlet into a fluid receptacle for mixing with the sample containing an analyte, wherein forcing the mixture in the pumping chamber to dispense the mixture comprises reducing the volume of the pumping chamber with the plunger; and • performing the measurement on the sample containing an analyte using an analytical unit.