Chromatography and NMR Flashcards
what is chromatography?
is a technique used for separating the components of a mixture on the basis of difference in their affinities for a stationary and for a moving phase
why is chromatography used?
provides and important method of separating and identifying components in a mixture
in chromatography, there is always a fixed..?
stationary phase through which passes a moving phase containing the mixture to be separated
What does separation in chromatography depends on?
the balance between solubility in the moving phase and retention in the stationary phase
Chromatography can either be..?
Analytical or Preparative
what is analytical chromatography?
Analytical chromatography involves the analysis of small amounts of material
what does analytic chromatography try to identify?
tries to identify and measure the relative amounts of various components present in the mixture
How is the resulting chromatogram compared?
the resulting chromatogram is compared with a known ‘standards; (chromatograms of specific substances of a ,known concentration
What is Analytical chromatography used in?
used routinely in sport drug testing
What is preparative chromatography?
is a larger scale process used to separate a mixture of products at the end of a chemical reaction
Chromatographic separation falls into two categories, what are the two categories?
- Partition chromatography and adsorption chromatography
What is partition chromatography?
- separation depends on the balance between a solutes solubility in the moving phase and retention in the stationary phase
- Stationary phase - Thin, non-volatile liquid film on the surface of an inner solid or fibrous matrix (e.g paper - cellulose fibres)
- moving phase - liquid or gas
- solute molecules equilibrate (partition between 2 phases)
what is Adsorption chromatography?
- strongly adsorbed molecules travel more slowly in the moving phase than those that are only weakly adsorbed
- stationary phase - solid (e.g alumina- aluminium oxide, silica - silicon dioxide)
- moving phase - liquid or gas
- separation occurs when solute molecules become attached to adsorption sites on the solid
What are different chromatographic techniques?
- paper chromatography (Similar to TLC)
- thin-layer chromatography (TLC)
- column chromatography (CG)
- Gas chromatography (GC)
what is Paper Chromatography?
Used in schools to separate the different dyes in an ink solution or the different food additives (colours) in sweets.
What is a chromatogram?
a chromatogram is a pattern of separated substances obtained by chromatography
How can the number of substances be identified?
the number of substances present in a mixture is given by the number of spots on the chromatogram
How can compounds be identified?
Using their Rf values (under standard conditions)
How are mixture patterns compared with?
Known standards on the same chromatogram
How can Rf values be calculated?
Distance moved by substance/ distance moved by solvent front
Why is the Rf value different for the same substances?
The Rf value for a substance is different in different solvents
When is complete separation only possible?
sometimes complete separation is only possible by rotating the paper through 90°, changing the solvent and repeating the process (2D- paper chromatography)
What is Thin-layer Chromatography?
a plate is coated with a thin layer of a solid and a solvent moves up the plate
when is TLC used?
used routinely in laboratories by bench-top scientists -