A device for determining a fluid sample volume contained in a porous structure (104, 204 304), comprising: a holder configured to retain a container (102, 202) having a sample receiving compartment, wherein, in use, the porous structure is at least partially disposed in the sample receiving compartment, the porous structure being fluidly coupled to a sample application location; a camera configured to take a plurality of images of the porous structure over time; and a controller communicatively coupled to the camera and configured to, for each image: i. detect an area of the porous structure (104, 204, 304) in the image; ii. divide the area of the porous structure into a plurality of segments; iii. determine an optical saturation value for each one of the plurality of segments, wherein each of the optical saturation values correlates with a degree of sample saturation of the porous structure; iv. calculate, using the optical saturation value of at least one of the plurality of segments of the porous structure, a sample volume in the porous structure, and optionally also at least one of J a sample saturation speed from said plurality of images, and an indicator of sample quality, characterized in that the device further comprises a compressive actuator, for example a knife edge, configured to stop a sample from flowing from the sample application location to the porous structure (104, 204, 304), and in that the controller is further configured to v. calculate from the plurality of images taken over time the sample volume in the porous structure in real time and trigger the actuator to stop the sample flow to the porous structure (104, 204, 304) when the sample volume reaches a predetermined threshold. a holder configured to retain a container (102, 202) having a sample receiving compartment, wherein, in use, the porous structure is at least partially disposed in the sample receiving compartment, the porous structure being fluidly coupled to a sample application location; a camera configured to take a plurality of images of the porous structure over time; and a controller communicatively coupled to the camera and configured to, for each image: i. detect an area of the porous structure (104, 204, 304) in the image; ii. divide the area of the porous structure into a plurality of segments; iii. determine an optical saturation value for each one of the plurality of segments, wherein each of the optical saturation values correlates with a degree of sample saturation of the porous structure; iv. calculate, using the optical saturation value of at least one of the plurality of segments of the porous structure, a sample volume in the porous structure, and optionally also at least one of J a sample saturation speed from said plurality of images, and an indicator of sample quality, characterized in that the device further comprises a compressive actuator, for example a knife edge, configured to stop a sample from flowing from the sample application location to the porous structure (104, 204, 304), and in that the controller is further configured to v. calculate from the plurality of images taken over time the sample volume in the porous structure in real time and trigger the actuator to stop the sample flow to the porous structure (104, 204, 304) when the sample volume reaches a predetermined threshold. i. detect an area of the porous structure (104, 204, 304) in the image; ii. divide the area of the porous structure into a plurality of segments; iii. determine an optical saturation value for each one of the plurality of segments, wherein each of the optical saturation values correlates with a degree of sample saturation of the porous structure; iv. calculate, using the optical saturation value of at least one of the plurality of segments of the porous structure, a sample volume in the porous structure, and optionally also at least one of J a sample saturation speed from said plurality of images, and an indicator of sample quality, characterized in that the device further comprises a compressive actuator, for example a knife edge, configured to stop a sample from flowing from the sample application location to the porous structure (104, 204, 304), and in that the controller is further configured to v. calculate from the plurality of images taken over time the sample volume in the porous structure in real time and trigger the actuator to stop the sample flow to the porous structure (104, 204, 304) when the sample volume reaches a predetermined threshold.