A method of performing an optical measurement of an analyte in a processed biological sample using a cartridge, wherein the cartridge is operable for being spun around a rotational axis, wherein the cartridge comprises: - a support structure comprising a front face; - a fluidic structure for processing a biological sample into the processed biological sample, wherein the fluidic structure comprises a sample inlet for receiving the biological sample; and - a measurement structure recessed from the front face, wherein the measurement structure comprises a chromatographic membrane, wherein the measurement structure comprises a measurement structure inlet connected to the fluidic structure to receive the processed biological sample, wherein the measurement structure comprises an absorbent structure, wherein the chromatographic membrane extends from the measurement structure inlet to the absorbent structure, wherein the chromatographic membrane comprises a detection zone, wherein the measurement structure comprises an inlet air baffle (128, 128') connected to the front face, wherein the measurement structure (200, 300, 500, 700) further comprises a static cover for covering the chromatographic membrane, wherein the static cover comprises an optically transparent area, wherein the optically transparent area is fixed in alignment with the detection zone of the chromatographic membrane, wherein the measurement structure further comprises an outlet air baffle connected to the front face, wherein the measurement structure is vented by the outlet air baffle and the inlet air baffle (128, 128'), wherein the detection zone has a detection zone length in a radial direction, wherein the inlet air baffle has an inlet air baffle length in the radial direction, wherein outlet air baffle has an outlet air baffle length in the radial direction, and wherein the inlet air baffle length and/or the outlet air baffle length is greater than or equal to the detection zone length; wherein the method comprises: - placing the biological sample into the sample inlet; - controlling the rotational rate of the cartridge to process the biological sample into the processed biological sample using the fluidic structure; - controlling the rotational rate of the cartridge to allow the processed biological sample to flow from the measurement structure inlet to the absorbent structure via the chromatographic membrane, wherein the inlet air baffle reduces the evaporation of the processed biological sample during rotation of the cartridge; and - performing the optical measurement of the detection zone with an optical instrument. - a support structure comprising a front face; - a fluidic structure for processing a biological sample into the processed biological sample, wherein the fluidic structure comprises a sample inlet for receiving the biological sample; and - a measurement structure recessed from the front face, wherein the measurement structure comprises a chromatographic membrane, wherein the measurement structure comprises a measurement structure inlet connected to the fluidic structure to receive the processed biological sample, wherein the measurement structure comprises an absorbent structure, wherein the chromatographic membrane extends from the measurement structure inlet to the absorbent structure, wherein the chromatographic membrane comprises a detection zone, wherein the measurement structure comprises an inlet air baffle (128, 128') connected to the front face, wherein the measurement structure (200, 300, 500, 700) further comprises a static cover for covering the chromatographic membrane, wherein the static cover comprises an optically transparent area, wherein the optically transparent area is fixed in alignment with the detection zone of the chromatographic membrane, wherein the measurement structure further comprises an outlet air baffle connected to the front face, wherein the measurement structure is vented by the outlet air baffle and the inlet air baffle (128, 128'), wherein the detection zone has a detection zone length in a radial direction, wherein the inlet air baffle has an inlet air baffle length in the radial direction, wherein outlet air baffle has an outlet air baffle length in the radial direction, and wherein the inlet air baffle length and/or the outlet air baffle length is greater than or equal to the detection zone length; wherein the method comprises: - placing the biological sample into the sample inlet; - controlling the rotational rate of the cartridge to process the biological sample into the processed biological sample using the fluidic structure; - controlling the rotational rate of the cartridge to allow the processed biological sample to flow from the measurement structure inlet to the absorbent structure via the chromatographic membrane, wherein the inlet air baffle reduces the evaporation of the processed biological sample during rotation of the cartridge; and - performing the optical measurement of the detection zone with an optical instrument.