This produces a chromatogram where different samples can be compared to a reference material. Thin layer chromatography Thin chromatography (TLC) is similar to paper chromatography but instead of paper, the stationary phase is a thin layer of an inert substance (eg silica) supported on a flat, unreactive surface (eg a glass plate). TLC has some advantages over chromatography. For example: the mobile phase moves more quickly through the stationary phase the mobile moves more evenly through the stationary phase there is a range of absorbencies for the stationary phase TLC tends to produce more useful chromatograms than paper chromatography, which show greater separation of the components in the mixture - and are therefore easier to analyse. The distance a sample travels can depend on the size or the polarity of the molecules involved. Larger molecules take longer to move up the chromatography paper or TLC plate, whereas smaller molecules are more mobile. Likewise, the polarity of the molecules can affect how far the spots travel, depending on the type of solvent used. Polar molecules will be more strongly attracted to polar solvents, and so would move further if a polar solvent was used as opposed to a non-polar solvent. The distance that spots move can be compared to the overall distance the solvent has moved and comparisons and measurements made. Gas chromatography In gas chromatography (GC), the mobile phase is an inert gas (eg helium). The stationary phase is a very thin layer of an inert liquid on an inert solid support - such as beads of silica packed into a long thin tube (this flexible tube is coiled many times inside a thermostatically-controlled oven to keep it at a constant temperature). GC is used to separate complex mixtures. It is much better at this than thin-layer or paper chromatography.
This produces a chromatogram where different samples can be compared to a reference material. Thin layer chromatography Thin chromatography (TLC) is similar to paper chromatography but instead of paper, the stationary phase is a thin layer of an inert substance (eg silica) supported on a flat, unreactive surface (eg a glass plate). TLC has some advantages over chromatography. For example: the mobile phase moves more quickly through the stationary phase the mobile moves more evenly through the stationary phase there is a range of absorbencies for the stationary phase TLC tends to produce more useful chromatograms than paper chromatography, which show greater separation of the components in the mixture - and are therefore easier to analyse. The distance a sample travels can depend on the size or the polarity of the molecules involved. Larger molecules take longer to move up the chromatography paper or TLC plate, whereas smaller molecules are more mobile. Likewise, the polarity of the molecules can affect how far the spots travel, depending on the type of solvent used. Polar molecules will be more strongly attracted to polar solvents, and so would move further if a polar solvent was used as opposed to a non-polar solvent. The distance that spots move can be compared to the overall distance the solvent has moved and comparisons and measurements made. Gas chromatography In gas chromatography (GC), the mobile phase is an inert gas (eg helium). The stationary phase is a very thin layer of an inert liquid on an inert solid support - such as beads of silica packed into a long thin tube (this flexible tube is coiled many times inside a thermostatically-controlled oven to keep it at a constant temperature). GC is used to separate complex mixtures. It is much better at this than thin-layer or paper chromatography.
CfE-Higher-Unit-3-Summary-Booklet.docx