33 - Chromatography Flashcards
What is chromatography?
A family of separation techniques that depend on the principle that a small amount of mixture can be separated if dissolved in a solvent and then the resulting solution moves over a solid.
What is the mobile phase?
The substance that carries the soluble components of the mixture with it through the supporting medium.
What is the stationary phase?
A layer or coating on the supporting medium that interacts with the analytes.
What is the supporting medium?
A solid surface on which the stationary phase is bound or coated.
Why do the components of the mixture separate?
Each component has an unique balance between its affinity for the stationary phase and its affinity for the mobile phase.
What is the stationary and mobile phase in paper chromatography?
SP = Chromatography paper
MP = suitable solvent
How does paper chromatography work?
The solvent to moves the mixture up the chromatography paper, with different components traveling at different distances due to their varying affinities for the paper and the solvent.
What are the key considerations with paper chromatography?
Solvent level below the sample line
Lid used to saturate the chamber with the solvent, prevent the solvent from evaporating.
Paper chromatography - If the sample moves further up does it have a greater affinity for the stationary or mobile phase?
Mobile phase (more soluble in the solvent)
What is the formula for Rf?
distance travelled by the solvent
What are the issues with paper chromatography?
Components may have similar Rf values.
An unknown component may have no previous chemical to compare it with.
What is the stationary and mobile phase in thin-layer chromatography?
SP = silica mounted on a glass plate
MP = suitable organic solvent
What are the advantages of thin-layer chromatography over paper chromatography?
Faster
Smaller amounts of mixtures can be separated
Plates are more robust than paper
What is done if the components are colourless?
UV light
Locating agent is used which reacts with the components to give coloured compounds.
What are examples of locating agents?
Ninhydrin for amino acids, iodine vapor for various compounds
What is the stationary and mobile phase in column chromatography?
SP = powdered silica
MP = suitable organic solvent
How does column chromatography work?
The chromatography column is filled with solvent and silica powder.
Drops of the mixture is placed on top of the silica.
Tap opened to allow solvent to flow out.
Additional solvent added to replace that leaving.
Components travel through at different rates and separate.
Batches of the solvent collected at intervals.
The solvent in each batch is evaporated to obtain its components.
What is the retention time in terms of column chromatography?
The time taken for the component to move through the column.
What is the stationary and mobile phase in gas-liquid chromatography?
SP = Liquid absorbed onto an inert solid support (coating capillary tube)
MP = unreactive gas
How does gas-liquid chromatography work?
Very small amount of sample injected into the machine.
The capillary tube is contained in an oven.
The sample boils and is carried along the thin capillary tube by the inert carrier gas.
The capillary tube contains a liquid stationary phase absorbed onto an inert solid.
The components of the mixture separate as some move with the gas and some are retained by the stationary phase, to different degrees.
What is retention time in terms of liquid-gas chromatography?
The time taken for the compound to travel to the detector, from the time the sample is injected to the time its peak shows a maximum height.
What is a chromatograph graph?
A visual representation of the different components in the sample.
What does the area under a peak represent in a chromatograph graph?
It is proportional to the amount of that component.
What is a use of liquid-gas chromatography?
Drug testing
