3.3.16 Chromatography

Question 1

What is chromatography

Answer 1

Separation techniques
Depend on principle that mixture can be separated if it is dissolved in a solvent and then the resulting solution (mobile phases) moves over a solid (stationary phase)

Question 2

Mobile phase

Answer 2

Carries soluble components of the mixture with it. The more soluble the component, the faster it moves - higher affinity for mobile phase. Solvent in mobile phase called eluent in column chromatography

Question 3

Stationary phase

Answer 3

Holds back components in the mixture that are attracted to it. The higher infinity, a component in mixture has for stationary phase, the slower it moves in the solvent

Question 4

Separation (chromatography) depends on

Answer 4

The balance between solubility in the mobile and retention in the stationary phase

Question 5

Thin-layer chromatography

Answer 5

A plate (glass metal or plastic sheet coated with thin layer silica gel or alumina - stationary phase) is coated with a solid and a solvent moves up the plate. UV light/chemical spraying locating agent may be required to see the components of the mixture and give colourful compounds

Question 6

Advantage of thin-layer over paper chromatography

Answer 6

Runs faster
Smaller amounts of mixture can be separated
Spots usually spread out less
Plates are more robust that paper

Question 7

Column chromatography

Answer 7

A column is packed with a solid such as silica, aluminium oxide or resin as the stationary phase and a solvent (eleunt) moves down the column. As solvent moves down the column, the compounds move at different rates and can be collected by flasks at the bottom

Question 8

Advantages of column chromatography

Answer 8

Large amounts of the mixture can be separated and collected e.g. a mix of amino acids can be separated into its pure components
More than one element can be used- better separation

Question 9

Gas-liquid chromatography

Answer 9

Stationary phase: column packed with solid powder
Mobile phase: unreactive, high pressure gas like helium or nitrogen
After injection, gas is carried along by the column and mixture separated into components as some components move along with the gas and are retained by the oil
Detectors required

Question 10

Gas chromatography mass spectrometry

Answer 10

Combination of both analytical techniques
Molecules separated by gas chromatography
Then put into mass spectrometer to be accurately identified

Question 11

Reagent to hydrolyse protein

Answer 11

Conc HCl

Question 12

How to see spots on TLC plates

Answer 12

Uv light
Ninhydrin

Question 13

Why might 2 solvents be required for chromatography

Answer 13

Some don’t dissolve in first

Question 14

What kind of bonding is linked to sample moving slower

Answer 14

Hydrogen bonding

Question 15

Why will different substances show different Rf values

Answer 15

They are bonded differently- more polar bonds mean longer retention time (smaller Rf) so hydrogen bonding/dipoles are attracted more strongly to stationary phase

Question 16

How to confirm identity of substance from Rf value

Answer 16

Compare your Rf value to the accepted Rf values for that substance in the same solvent and set up

Question 17

GLC advantages

Answer 17

Very sensitive
Can trace traces of substances in foodstuffs
Link oil pollution on beaches to the specific tanker the oil came from

Question 18

GLC uses

Answer 18

Test athletes and horses’ blood and urine for drugs

Question 19

How can you use GC or GCMC to identify substances

Answer 19

Match gas chromatograph to that of a known under the same conditions- retention times match
Confirmed using mass spectroscopy, NMR or infrared spectroscopy