Why are repeated mixing steps used while reducing the particle size of a laboratory sample?

In the context of analytical chemistry, repeated mixing steps are essential during the particle size reduction of a laboratory sample to ensure the material remains representative throughout the process.1

When a sample is reduced in a series of steps, each stage of grinding—or comminution—must be followed by an interval of mixing to counteract the natural tendency of particles to segregate based on their physical properties, such as size, shape, and density. Without these mixing intervals, fine particles may collect in the center of a pile while larger or rounded particles migrate to the edges, leading to an uneven distribution of the analyte.1

By incorporating consistent mixing, the analyst ensures that the subsample remains uniform, which is critical for maintaining the integrity of the test sample before the final test portions are selected for determination.1