Chromatography
No description yet. This curated deck is ready for daily study.
Card preview (24)
What is the purpose of paper chromatography?
It is a separation technique used to separate dyes
What does TLC stand for?
Thin layer chromatography
What is TLC?
A development of the paper chromatography where the filter paper is replaced by a glass, metal or plastic sheet coated with a thin layer of silica gel (SiO2) or alumina (Al2O3) which acts as a stationary phase. These are often called plates.
What are the advantages of TLC over paper chromatography?
• Faster • Smaller amounts of mixtures can be separated • Spots are usually spread out less • The plates are more robust than paper
How can the positions of colourless spots on a chromatogram be located?
By shining UV light on the plate OR by chemically spraying the plate with a locating agent which reacts with the components of the mixture to give coloured compounds.
What is TLC often used to separate?
Mixtures of amino acids.
How to calculate the Rf value?
Distance moved by spot/distance moved by solvent (all Rf values must be below 1)
What are Rf values used for?
Identifying each component
What does column chromatography use?
A powder such as silica, aluminium oxide or a resin (stationary phase).
How does column chromatography work?
A column is packed with a solid and a solvent moves down the column
How can you get a better separation in column chromatography?
Use more than one eluent
What are the advantages of column chromatography?
Large amounts can be separated and collected. You can separate amino acids into its pure components using this technique. More than one eluent can be used.
What is the stationary phase in gas-liquid chromatography?
A powder coated in oil. It is either packed into or coated onto the inside of a long capillary tube and placed in an oven.
What is the mobile phase in gas-liquid chromatography?
Usually it is an unreactive gas e.g. nitrogen or helium.
What happens during gas-liquid chromatography?
After injection, the sample is carried along by the gas and the mixture separates as some of the components move along with the gas and some are retained by the oil each to a different degree. Thus the components leave the column at different times after injection so they have different retention times.
In a typical GC trace what are the x and y axis?
x axis - retention time y axis - signal from detector
What is the area under each peak in a GC trace?
The area under each peak is proportional to the abundance of that component.
What is an advantage of GC?
It is extremely sensitive so it can separate minute traces of substances in foodstuffs and even link crude oil pollution found on beaches with its tanker of origin by comparing oil samples.
What is GC used for commonly?
Testing athletes’ blood or urine for drug taking
How is a component identified using GC?
By matching its retention time with that of a known substance under the same conditions. This is then confirmed by comparing the mass spectra of the two substances.
What is GCMS?
Gas chromatography mass spectrometry
What is the mass spectrometer used as in GCMS?
As the detector for a gas chromatography system
Describe GCMS.
As each component of a mixture comes out of the gas chromatography column, the time it has taken to pass through the column (Retention time) is noted. Each component is fed automatically into mass spectrometer which enables the compound to be identified either by its fragmentation pattern or by measuring its accurate mass.