A sample holder for holding a fluid container for performing optical analysis of a fluid sample contained within the container, the holder comprising: a base having an upright backing member; and a movable upright clamping member configured to move relative to the backing member between an open, retracted position, in which the clamping member no longer contacts the container, and a closed, holding position, in which the clamping member presses against the container to lightly clamp the container between the clamping member and the backing member whereby the container is immobilized for optical analysis of the fluid sample in the container, wherein the backing member and the clamping member comprise substantially horizontal slots (111, 121) to provide optical access to the fluid sample when held in the sample holder to enable collection of scattered light at an angle relative to light incident on the fluid sample, and wherein: at least one first heating/cooling element (112a, 112b) connected to an inwardly facing surface of the backing member, the first heating/cooling element being capable of transferring heat to or from the fluid sample in the container; at least one first heat-conductive plate (114a, 114b) connected to an inwardly facing surface of the first heating/cooling element (112a, 112b) for conducting heat to or from the fluid sample in the container; at least one second heating/cooling element (122a, 122b) connected to an inwardly facing surface of the movable clamping member, the second heating/cooling element (122a, 122b) being capable of transferring heat to or from the fluid sample in the container; and at least one second heat-conductive plate (124a, 124b) connected to an inwardly facing surface of the second heating/cooling element (122a, 122b) for conducting heat to or from the fluid sample in the container. a base having an upright backing member; and a movable upright clamping member configured to move relative to the backing member between an open, retracted position, in which the clamping member no longer contacts the container, and a closed, holding position, in which the clamping member presses against the container to lightly clamp the container between the clamping member and the backing member whereby the container is immobilized for optical analysis of the fluid sample in the container, wherein the backing member and the clamping member comprise substantially horizontal slots (111, 121) to provide optical access to the fluid sample when held in the sample holder to enable collection of scattered light at an angle relative to light incident on the fluid sample, and wherein: at least one first heating/cooling element (112a, 112b) connected to an inwardly facing surface of the backing member, the first heating/cooling element being capable of transferring heat to or from the fluid sample in the container; at least one first heat-conductive plate (114a, 114b) connected to an inwardly facing surface of the first heating/cooling element (112a, 112b) for conducting heat to or from the fluid sample in the container; at least one second heating/cooling element (122a, 122b) connected to an inwardly facing surface of the movable clamping member, the second heating/cooling element (122a, 122b) being capable of transferring heat to or from the fluid sample in the container; and at least one second heat-conductive plate (124a, 124b) connected to an inwardly facing surface of the second heating/cooling element (122a, 122b) for conducting heat to or from the fluid sample in the container. at least one first heating/cooling element (112a, 112b) connected to an inwardly facing surface of the backing member, the first heating/cooling element being capable of transferring heat to or from the fluid sample in the container; at least one first heat-conductive plate (114a, 114b) connected to an inwardly facing surface of the first heating/cooling element (112a, 112b) for conducting heat to or from the fluid sample in the container; at least one second heating/cooling element (122a, 122b) connected to an inwardly facing surface of the movable clamping member, the second heating/cooling element (122a, 122b) being capable of transferring heat to or from the fluid sample in the container; and at least one second heat-conductive plate (124a, 124b) connected to an inwardly facing surface of the second heating/cooling element (122a, 122b) for conducting heat to or from the fluid sample in the container.