Thin layer chromatography (TLC) is normally carried out on single-phase (adsorbent) plates. However, it may be necessary to use nore than one adsorbent to achieve the separation of complex mixtures. Literature reports indicate that the use of mixed phases in TLC is not very common, possibly because the plates are difficult to prepare and precoated single-phase plates of different absorbents are readily available (silica gel, reversed phase, cellulose. alumina, etc.).