Thin layer chromotography
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49 Terms
What is separation science?
The use of techniques to separate components of a mixture.
Why is separation science important in pharmaceutical analysis?
To isolate, identify, and analyse compounds in complex mixtures.
Name three common chromatographic techniques
TLC, GC, HPLC.
Name four non-chromatographic separation methods.
Filtration, centrifugation, distillation, liquid-liquid extraction.
What is the basis of all chromatographic separations?
Partitioning between a mobile phase and a stationary phase.
What is the stationary phase?
The phase that remains fixed during chromatography.
What is the mobile phase?
The phase that moves through the stationary phase carrying analytes
What determines how far a compound travels in chromatography?
Its relative affinity for the stationary and mobile phases.
Which compounds move furthest in chromatography?
Compounds with greater affinity for the mobile phase.
What is an eluent?
The mobile phase.
What is elution?
The movement of the mobile phase and analytes through the stationary phase.
What is effluent?
The mobile phase and analytes exiting the chromatographic system.
What is resolution?
The degree of separation between compounds.
What does TLC stand for?
Thin Layer Chromatography.
Who introduced TLC
Stahl in 1956.
What is the principle of TLC?
Compounds separate due to different affinities for the stationary and mobile phases.
How does the mobile phase move through a TLC plate?
By capillary action.
What is the stationary phase in TLC?
A thin layer of adsorbent coated onto a plate.
What materials can TLC plates be made from?
Glass, plastic, or aluminium.
What is the most common TLC stationary phase?
Silica gel.
What are the properties of silica gel?
Polar, hydrophilic, and acidic.
What is the mobile phase in TLC?
A solvent or solvent mixture.
What is the origin in TLC?
The point where the sample is applied.
Why do polar compounds travel less distance on silica TLC plates?
They interact more strongly with the polar stationary phase.
Why do non-polar compounds travel further on silica TLC plates?
They interact less strongly with the stationary phase.
What happens to Rf values when mobile phase polarity increases?
Rf values generally increase.
What is the purpose of visualisation in TLC?
To detect colourless compounds after separation.
Why is UV detection commonly used in TLC?
Most drugs contain UV-absorbing chromophores.
What is seen under UV 254 nm?
Purple spots on a green background
What type of TLC detection is UV visualisation?
Non-destructive.
What does iodine vapour detect?
Many organic compounds, producing brown spots.
What does ninhydrin detect?
Primary and secondary amines.
What colour does ninhydrin produce after reaction?
Ruhemann's purple.
What are examples of compounds detected by ninhydrin?
Amino acids and aminoglycoside antibiotics.
What is the Rf value?
Distance travelled by compound ÷ distance travelled by solvent front.
What information does an Rf value provide?
A characteristic value used to identify a compound.
How are Rf values commonly reported in pharmaceutical analysis?
As Rf × 100.
How can TLC be used to identify compounds?
By comparing Rf values with known standards.
How can TLC detect impurities?
Additional spots indicate the presence of impurities.
What does the number of spots on a TLC plate indicate?
The number of components present.
What does spot intensity indicate?
The relative amount of compound present.
Is TLC qualitative, quantitative, or both?
Mainly qualitative but can provide semi-quantitative information.
What is a major pharmaceutical application of TLC?
Identification of drugs.
How is TLC used in pharmacopoeias?
For identification and impurity testing.
What is a limit test?
A test to determine whether impurity levels exceed acceptable limits.
What are the main advantages of TLC?
Simple, cheap, flexible, robust, and suitable for analysing multiple samples.
What is a major advantage of TLC compared with many methods?
The entire chromatogram can be viewed at once.
What are the main limitations of TLC?
Lower sensitivity, lower separation efficiency, and unsuitable for volatile compounds.
Why does TLC require operator skill?
Reliable separations depend on correct solvent choice, spotting, and interpretation.