Quality control in sampling has been demonstrated as practicable in sampling procedures that require the combination of sample increments to form a composite sample. The proposed method requires no sampling resources or use of time beyond those normally used. Increments are allocated at random into two half-sized composites, each of which is analysed separately. The absolute difference between the two results is plotted on a one-sided control chart, which is interpreted like a Shewhart chart. In commonly prevailing circumstances the analytical precision is negligible and the chart represents sampling precision alone.