There is described a sample holder and associated fluid container assembly for optical analysis of a fluid sample within a translucent container of the fluid container assembly. The sample holder includes clamping members rotatably mounted to a frame for rotation, about parallel axes spaced apart from each other, between a container accepting position in which the clamping members are spaced apart from the translucent container, and an analysis position in the clamping members abut the translucent container. The clamping members each define an optical waveguide slot extending therethrough that is substantially aligned with the translucent container when the clamping members are disposed in the analysis position, to thereby provide optical access to the translucent container for optical analysis of the fluid sample therein.