Figure 2 : Even the best packaged portion of HPTLC plates whether glass, plastic or aluminium based, are either from the very beginning or a few minutes after opening the package NOT ready for chromatography. The plate surface is quickly sorbing all available traces from the gas phase around. No qualified analyst would inject a sample into a non cleaned HPLC column. IN PLC not only visible but all non visible traces determine the chromatography. Some producers of ready made plates do not or cannot use enough clean water during the production procedure. Thus plate pre cleaning is a must. By circular PLC this is a enough quick and - if well done - perfect procedure: the proper cleaning mobile phase is in the phase bottle seen above. “Proper” however may be a problem for some analysts: A chemically treated plate needs other clean up phases than a standard HPTLC SiO2 phase. The cleaning liquid must have a very good solubility force for all to be removed sorbed plate impurities, should not destabilize the stationary phase, must be completely removable by flowing gas at room temperature etc. etc. Quite often methanol plus CH2Cl2 is a good cleaning phase mix. Very important is a well done drying step - at room temperature by the 2 L/min aquarium pumped gas flow - it may need 3...5 minutes at 20 degr. C.