chromatography Flashcards
what is TLC
a plate is coated with a solid and a solvent moves up the plate
column chromatography?
a column is packed
with a solid and a solvent moves down the column
gas chromatography
a column is packed with a
solid or with a solid coated by a liquid, and a gas is passed through the column under pressure at high temperature
what’s the MP in gas chromatography
inert gas such as nitrogen, helium, argon
whats the SP in GC
high boiling point liquid on an inert solid
Separation by column chromatography depends on
the balance between solubility in the moving phase and retention in the stationary phase
A solid stationary phase separates by
adsorption
A liquid stationary phase separates by
relative solubility
WHEN Two directional chromatography
This process would be done if components in the mixture have the same Rf value or if some components are not soluble in the first solvent
METHOD for Two directional chromatography
A spot of the mixture on a TLC plate is first separated with one solvent.
Then the TLC plate is rotated 90o and the plate is placed in a second solvent for a second separation to take place
Simple column chromatography
- A glass tube is filled with the stationary phase usually silica or alumina in powder form to increase the surface area.
- A filter or plug is used to retain the solid in the tube. Solvent is added to cover all the powder.
- The mixture to be analysed is dissolved in a minimum of a solvent and added to the column.
- A solvent or mixture of solvents is then run through the column.
- The time for each component in the mixture to reach the end of the column is recorded (retention time)
Gas-Liquid Chromatography used for
separate mixtures of volatile liquids.
why It is important to use an inert carrier gas such as helium or nitrogen.
These will not react with the components being separated in the GC column.
The following factors can be changed to change the retention times of substances being separated:
GC column temperature, column length , flow rate.
If the temperature or the flow rate is higher then substance will move more quickly through the column to give shorter retention times.
what is GC-MS
It is also possible for gas-liquid chromatography machine to be connected to a mass spectrometer, IR or NMR machine, enabling all the components in a mixture to be identified.
GC-MS is used in analysis, in forensics, environmental analysis, airport security and space probes.
Most commonly a mass spectrometer is combined with GC to generate a mass spectra which can be analysed or compared with a spectral database by computer for positive identification of each component in the mixture.
