Rotatable cartridge with a metering chamber for analyzing a biological sample

A method of performing a measurement of a processed biological sample using a cartridge, wherein the cartridge is operable for being spun around a rotational axis, wherein the cartridge comprises:

• an aliquoting chamber;
• a metering chamber, wherein the metering chamber has side wall regions and a central region, wherein the side wall regions are narrower than the central region in a cross sectional view of the metering chamber, wherein capillary action next to the side wall regions of the metering chamber is greater than in the central region of the metering chamber,
• a connecting duct for connecting the metering chamber with the aliquoting chamber, wherein the connecting duct comprises a duct entrance in the aliquoting chamber, wherein the connecting duct further comprises a duct exit in the metering chamber, wherein a circular arc about the rotational axis passes through both the duct entrance and the duct exit;
• a downstream fluidic element, wherein the downstream fluidic element is connected to the metering chamber via a valve;
• a fluidic structure for processing a biological sample into the processed biological sample, wherein the fluidic structure comprises the downstream fluidic element, wherein the downstream fluidic element is fluidically connected to the fluidic structure, wherein the fluidic structure comprises a measurement structure for enabling measurement of the processed biological sample, wherein the fluidic structure is configured for receiving the biological sample;
• wherein the method comprises the steps of:
• placing the biological sample into the fluidic structure;
• controlling the rotational rate of the cartridge to process the biological sample into the processed biological sample using the fluidic structure;
• filling the aliquoting chamber with a fluid;
• decreasing the rotational rate of the cartridge to permit the fluid in the aliquoting chamber to flow into the connecting duct and to fill the metering chamber a first time;
• increasing the rotational rate of the cartridge to transfer a first part of the fluid from the metering chamber through the valve and to transfer a first remaining part back into the aliquoting chamber;
• decreasing the rotational rate of the cartridge to permit the fluid in the aliquoting chamber to flow into the metering chamber and to fill the metering chamber a second time;
• increasing the rotational rate of the cartridge to transfer a second part of the fluid from the metering chamber through the valve and to transfer a second remaining part back into the aliquoting chamber;
• performing the measurement using the measurement structure and using a measurement system;
• and
• a vent, wherein the vent is connected to the metering chamber, wherein the vent is nearer to the rotational axis than the metering chamber.