33.1 Chromatography Flashcards
What principle does chromatography depend on
That all mixtures can be separated if dissolved in solvent and then the resulting solution (now called mobile phase) is moved over a solvent.
Every component has a unique balance between its affinity for the stationary and for the mobile phase.
What does the mobile phase do
It carries the soluble parts of mixture with it. The more soluble the component in the mobile phase, the faster it moves
What is the stationary phase
It will hold back the components of the mixture that are attracted to it. The more affinity one of these components has for stationary phase, the slower it will move.
What is thin layer chromatography
It is a development of paper chromatography, but the filter paper is replaced by either…
- Glass
- Metal
- Plastic sheet coated with a thin layer of silica gel
- Al2O3
These act as a stationary phase
Advantages of thin layer chromatography over paper chromatography
It runs faster so quicker process of separation
Smaller amounts of mixture can be separated
Spots spread out less so are more precise to be measured better
Plates are more robust than paper
Once chromatography has occurred how do you find position of colourless spots
Ultraviolet light is shone onto plate to locate it
Or spray a locating agent which reacts with the components to give coloured compounds
How is rf value measured
RF = Distance moved by spot divided by total distance moved by solvent
What is the stationary phase of column chromatography made of
It uses a powder such as silica, aluminium oxide or resin as the stationary phase
How does column chromatography work
The powder is packed into a narrow tube (the column)
The solvent (called the eluent) is added on top and runs down the column so components of mixture move at different rates and can be collected separately in flasks at the bottom
You can use multiple eluents to get better separation
Advantage of column chromatography
Large amounts of mixture can be separated and collected
Eg amino acids can be separated into their components by this method
Gas liquid chromatography:
What is the stationary phase
What is mobile phase
Stationary phase is a powder coated with oil which is placed in a long capillary tube which is coiled up and placed in oven
Mobile phase is a gas eg nitrogen or helium
Process of gas liquid chromatography
.Powder coated with oil is placed in a long capillary tube which is coiled up and placed in oven
The sample is carried along by gas and the mixture separates as some of the components move along with the gas and some are retained by the oil.
This means the components leave column at different times after injection so have different retention times
How does graph of these work
Retention time on x axis and signal from detector on y axis
Area under each peak is proportional to that amount of component
Advantage of Gas liquid chromatography
Incredibly sensitive and can separate minute traces of substances
It can also identify components:
By matching the retention time of a substance with the retention time of a known compound under the same conditions
What is Gas chromatography mass spectrometry
- A mass spectrometer is used to detect gas chromatography system
Each component of mixture comes out of a gas chromatography column, so the retention time is noted
Each component is fed to mass spectrometer which enables them to be identified by fragmentation pattern or measuring its accurate mass
