Chromatography Flashcards
Stationary phase
Mixture passes over in order to be separated
Mobile phase
Mixture carried over the solid material. Either gas or liquid
Affinity refers to
Stationary phase
Solubility refers to
Mobile phase
High affinity to stationary phase
Means components of mixture will travel slowly
Low solubility in the mobile phase
Travel slowly with the solvent
3 types of chromatography
- Thin layer chromatography = plate is coated in a solid and moves up the plate
- Column chromatography = columns is packed with solid and solvent moves down the column
- Gas chromatography = column is packed with a a solid and coated with a liquid and a gas is passed throhhh the chum at high pressure and temperature
TLC method
- Wearing gloves draw a line 1cm above the bottom the the TLC plate
- Use a capillary tube to add tiny drops of each solution at equal distances and allow to dry
- Add solvent to large beaker with a slid no more than 1cm in depth
- Place TLC plate into chamber make sure that the solvent is below the pencil line
- When the level of the solvent reaches 1cm from the top of the plate remove and mark with a pencil line and allow to dry in a fume cupboard
- Place under a sub light to see the spots
Calculate rf value
Why use a pencil line
So will not dissolve in solvent and mix with spots
Why use small drops
Large drops will cause spots to merge
Why use lid
To prevent evaporation of toxic solvent
Why do you wear gloves
So no contamination on hands from plate
Why use uv light
Spots are colourless and not visible
Rf equation
Distance moved by spot / distance moved by solvent
Column chromatography
- A glass tube is filled with a stationary phase usually silica in powered form to increase surface area
- Solvent is added to cover all the powder
- Mixture is dissolved in a mimum of solvent and added to column
- The mixture then runs through the column
The time taken to reach the end is recorded
What is gas chromatography used for
Used to separate mixture of volatile solvent that can easily evaporate. Measure sthe time taken from the injection to the detector
What the gas
Inert gas in the mobile phase which is sully helium
Stationary phase is also inert
What will basic gas liquid chromatography tell us
The number of peaks which shows the abundance and can be connected to a IR or mass spectra to identify the compound
Advantage of TLC
Faster than paper
Work on small samples
Can be used to determine when a chemical reaction is complete
Limitations of TLC
Similar compounds have similar Fr values
Condition must be kept constant
Cannot be used fir large quantities
Difficult to find a solvent that separates all components ina a mixture
Polar molecules have
A higher affinity to the stationary phase so travel slower so smaller rf value
Area of the peaks
Proportional to amount of components in a. a mixture
Limitations of gas chromatography
Peaks may be hidden
No reference retention times
Similar retention times / peaks
Uses of gas chromatography
Forensic
Environmental analysis
Airport security
