Abstract: An assembly for maintaining a fluid sample in a homogeneous state. The assembly includes a mechanical mixer comprised of an annular ring positioned within a collection chamber of the assembly. The annular ring is comprised of a material compatible to the fluid and having a density less than that of the fluid to be collected in the collection chamber. By inverting the assembly once the fluid sample has been collected within the collection chamber, the annular ring forming the mechanical mixer is caused to be translated through the fluid to float on a top surface of the fluid. Translation of the annular ring through the fluid causes mixing of the fluid to thereby maintain the fluid in a homogeneous state.