Chromatography, the separation of mixtures by passing a mobile phase through a stationary phase, is a common technique used in most clinical and research laboratories. Media, the substance of the stationary phase, can be packed into an empty tube, also known as a column, by a laboratory technician. Empty columns are available for purchase which can then be used and discarded, or cleaned and used multiple times. The appropriate column will depend on the sample type, the purification method and the laboratory system. Mixtures can be separated by gravity, vacuum pressure or centrifugation. Small scale applications can be done with minimal sample volume; large production, or bioprocess, can be done on a manufacturing scale.