<Ul> <Li> Using a capillary, a small spot of solution containing the sample is applied to a plate, about 1.5 centimeters from the bottom edge . The solvent is allowed to completely evaporate off to prevent it from interfering with sample's interactions with the mobile phase in the next step . If a non-volatile solvent was used to apply the sample, the plate needs to be dried in a vacuum chamber . This step is often repeated to ensure there is enough analyte at the starting spot on the plate to obtain a visible result . Different samples can be placed in a row of spots the same distance from the bottom edge, each of which will move in its own adjacent lane from its own starting point . </Li> <Li> A small amount of an appropriate solvent (eluent) is poured into a glass beaker or any other suitable transparent container (separation chamber) to a depth of less than 1 centimeter . A strip of filter paper (aka "wick") is put into the chamber so that its bottom touches the solvent and the paper lies on the chamber wall and reaches almost to the top of the container . The container is closed with a cover glass or any other lid and is left for a few minutes to let the solvent vapors ascend the filter paper and saturate the air in the chamber . (Failure to saturate the chamber will result in poor separation and non-reproducible results). </Li> <Li> The TLC plate is then placed in the chamber so that the spot (s) of the sample do not touch the surface of the eluent in the chamber, and the lid is closed . The solvent moves up the plate by capillary action, meets the sample mixture and carries it up the plate (elutes the sample). The plate should be removed from the chamber before the solvent front reaches the top of the stationary phase (continuation of the elution will give a misleading result) and dried . </Li> <Li> Without delay, the solvent front, the furthest extent of solvent up the plate, is marked . </Li> <Li> The plate is visualized . As some plates are pre-coated with a phosphor such as zinc sulfide, allowing many compounds to be visualized by using ultraviolet light; dark spots appear where the compounds block the UV light from striking the plate . Alternatively, plates can be sprayed or immersed in chemicals after elution . Various visualising agents react with the spots to produce visible results . </Li> </Ul> <Li> Using a capillary, a small spot of solution containing the sample is applied to a plate, about 1.5 centimeters from the bottom edge . The solvent is allowed to completely evaporate off to prevent it from interfering with sample's interactions with the mobile phase in the next step . If a non-volatile solvent was used to apply the sample, the plate needs to be dried in a vacuum chamber . This step is often repeated to ensure there is enough analyte at the starting spot on the plate to obtain a visible result . Different samples can be placed in a row of spots the same distance from the bottom edge, each of which will move in its own adjacent lane from its own starting point . </Li> <Li> A small amount of an appropriate solvent (eluent) is poured into a glass beaker or any other suitable transparent container (separation chamber) to a depth of less than 1 centimeter . A strip of filter paper (aka "wick") is put into the chamber so that its bottom touches the solvent and the paper lies on the chamber wall and reaches almost to the top of the container . The container is closed with a cover glass or any other lid and is left for a few minutes to let the solvent vapors ascend the filter paper and saturate the air in the chamber . (Failure to saturate the chamber will result in poor separation and non-reproducible results). </Li> <Li> The TLC plate is then placed in the chamber so that the spot (s) of the sample do not touch the surface of the eluent in the chamber, and the lid is closed . The solvent moves up the plate by capillary action, meets the sample mixture and carries it up the plate (elutes the sample). The plate should be removed from the chamber before the solvent front reaches the top of the stationary phase (continuation of the elution will give a misleading result) and dried . </Li>

What does the filter paper do in tlc
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