Thin-layer chromatography
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Define the term 'stationary phase' in the context of thin-layer chromatography (TLC). Give an example.
The stationary phase is the solid material on which the separation occurs in TLC. It is typically a thin layer of a substance like aluminium oxide (Al₂O₃) or silica gel supported on a glass or plastic plate.
Define the term 'mobile phase' in the context of thin-layer chromatography (TLC). What is its role?
The mobile phase is the solvent that moves through the stationary phase in TLC, carrying the compounds to be separated. Its polarity influences the relative solubility and movement of different compounds.
Define the Rf value in thin-layer chromatography (TLC).
The Rf value (retardation factor) is the ratio of the distance traveled by the compound to the distance traveled by the solvent front in TLC. Rf = (distance traveled by compound) / (distance traveled by solvent front).
Explain how the interaction with the stationary phase affects the Rf value of a compound in TLC.
Stronger interactions with the stationary phase result in a smaller Rf value, as the compound spends more time adsorbed to the stationary phase and travels a shorter distance up the plate. Weaker interactions lead to higher Rf values.
Explain how the relative solubility of a compound in the mobile phase affects its Rf value in TLC.
Greater solubility in the mobile phase leads to a larger Rf value. The compound is more readily dissolved and carried further up the TLC plate by the solvent.
Describe the stationary phase in gas-liquid chromatography (GLC).
In GLC, the stationary phase is a high-boiling point, non-polar liquid coated on an inert solid support (
Describe the mobile phase in gas-liquid chromatography (GLC).
The mobile phase in GLC is an unreactive carrier gas, such as helium or nitrogen. It's role is to transport the vaporized sample through the column without interacting with it.
Define 'retention time' in gas-liquid chromatography (GLC).
Retention time is the time it takes for a particular compound to travel from the injection point to the detector in GLC. It is used to identify compounds.
How can you interpret a gas/liquid chromatogram to determine the percentage composition of a mixture?
The area under each peak in a GLC chromatogram is proportional to the amount of that component in the mixture. The percentage composition is determined by calculating the percentage of each peak area relative to the total area of all peaks.
Explain how interaction with the stationary phase affects retention times in gas-liquid chromatography (GLC).
Compounds with stronger interactions with the stationary phase will have longer retention times, as they spend more time dissolved in the liquid phase and are therefore slower to pass through the column. Weaker interactions result in shorter retention times.
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