A mixing apparatus (200) is disclosed which comprises a) a mixing well (252) characterized by an internal volume not exceeding 100 ml.; b) a drive mechanism including a stationary circumferential gear (254) on an inner surface of the mixing well; c) a planetary mixing element (240) driven by a mixing element gear (270) which engages the stationary circumferential gear; and d) a central mixing element (230) positioned substantially at a center of the mixing well; wherein the planetary mixing element revolves around the central mixing element.