Chromatography Flashcards
What are the components of the moving phase in TLC?
Solvent
The solvent carries the samples up the TLC plate.
What is the stationary phase in TLC made of?
Silica gel or alumina on aluminum, glass, or plastic
The stationary phase interacts with the compounds being separated.
What is the purpose of adding a fluorescent compound to the TLC plate?
To aid in visualisation under UV light
Why should TLC plates be held by the edges?
To prevent contamination from hands
Why must the solvent level be below the baseline in TLC?
So the sample spots don’t dissolve in the solvent
What causes the solvent to rise in TLC?
Capillary action
When should the TLC plate be removed from the chamber?
When the solvent front is ~1cm from the top
How are spots visualized in TLC using UV light?
The fluorescent background glows and sample spots quench the glow
What is another method to visualize TLC spots besides UV?
Using a stain or developing agent like ninhydrin
What is Rf in chromatography?
The ratio of the distance moved by the compound to the distance moved by the solvent front
How does polarity affect movement in TLC?
More polar compounds move slower; less polar move faster
Can TLC be used for paper chromatography?
Yes
What are common uses of Rf values?
Compound identification and monitoring reactions
What is the apparatus called in chromatography?
Chromatograph
What is the pattern of separated substances called?
Chromatogram
What does retention time refer to?
Time a component stays in the column
What is chromatography in general terms?
A technique for separating mixtures based on affinities to phases
What is the moving phase in gas chromatography (GC)?
Carrier gas (e.g., He or N₂)
What is the stationary phase in GC?
Non-volatile liquid film on inert powder in a coiled tube
How is the sample introduced in GC?
Injected in vaporized form into the column
What does longer retention time indicate in GC?
Stronger interaction with the stationary phase
What affects retention time and resolution in GC?
Gas flow rate, column length, and operating temperature
How does gas flow rate affect resolution in GC?
Higher flow rate = lower retention time = lower resolution
How does column length affect resolution in GC?
Longer column = higher resolution
How does temperature affect GC analysis?
Alters retention time and peak separation
How are components detected in GC?
By detectors which produce a chromatogram with peaks
What does the area under a peak in GC represent?
The quantity of that component
What are key uses of gas chromatography?
Separation of volatile compounds, trace analysis, and structure identification
What is GC-MS?
Gas chromatography-mass spectrometry
What is the stationary phase in column chromatography?
Silica or alumina powder
What is the moving phase in column chromatography?
Eluent (a pure solvent or mixture)
What is the process of adding eluent to a column called?
Elution
How is the column packed in column chromatography?
With finely divided silica or alumina
What happens after adding the sample in column chromatography?
Solvent is added to wash the sample down the column
How are fractions collected in column chromatography?
In test tubes at intervals
How is TLC used in column chromatography?
To check the contents of fractions
How are compounds recovered after separation in column chromatography?
Evaporating the solvent from combined fractions
Which compounds travel slowest in column chromatography?
Most polar compounds
Why do polar compounds move slower in column chromatography?
They adsorb more strongly to the stationary phase
What is the advantage of column chromatography over TLC?
It can separate larger amounts of sample
What is the purpose of chromatography in general?
To separate and identify components in a mixture
What is a carrier gas?
An inert gas used to transport samples in gas chromatography
What is capillary action?
The movement of liquid through a porous material due to intermolecular forces
What is the mobile phase?
The phase that moves through the stationary phase and carries the components
What does ‘eluent’ refer to?
The solvent used in column chromatography to carry compounds through the column
Why is visualisation important in TLC?
To detect colorless compounds
What causes different movement rates in chromatography?
Differences in compound polarity and interaction with the phases
What does a peak on a chromatogram represent?
A specific compound in the sample
Why use a lid in TLC chambers?
To saturate the chamber and prevent solvent evaporation
Why use inert gases in GC?
They don’t react with the sample or stationary phase
