chromatography techniques

Question 1

what is chromatography used for

Answer 1

used to separate and analyse small amounts of mixtures and to determine the composition and purity of substances

Question 2

how are the components separated in a stationary and mobile phase

Answer 2

• different types of polar groups
  amount of charged and polar - -
• chemical group
• molecular weight
• geometry
• position and numbers of carbon carbon double bonds.

Question 3

what is the stationary phases

Answer 3

solid or liquid on which components can bond/interact/absorb to
when components interact with the stationary phase, it slows their motion

Question 4

what is the mobile phase

Answer 4

a liquid or gas that passes over or through the stationary phase. it dissolves and carries the components of the mixture with it.

Question 5

what is the stationary and mobile phase in paper chromatography

Answer 5

stationary: chromatography paper
mobile: suitable solvent (water, ethanol etc.)

Question 6

what is the separation in paper chromatography

Answer 6

as the solvent moves up the paper it dissolves the components and moves them up the paper. the more soluble a component is, the further up it moves.

Question 7

what is the retention factor

Answer 7

measure of a components tendency to move with the mobile phase

Question 8

formular for retention factor in paper chromatography

Answer 8

distance component moved from origin / distance solvent moved from the origin

Question 9

why might comparisions be a problem

Answer 9

different substances have similar Rf values

there is nothing to compare it with (eg new substance)

Question 10

what is thin layer chromatography (TLC)

Answer 10

faster and provides more separation than paper chromatography

Question 11

stationary phase and mobile phase in TLC

Answer 11

silica mounted on a glass plate - stationary

suitable or water solvent - mobile phase

Question 12

advantages of paper chromatography

Answer 12

• cheap
• little preparation
• more efficient for polar and water soluble compounds
• easy to handle and store

Question 13

what is high performance liquid chromatography and phases and separation (HPLC)

Answer 13

used for larger organic molecules

stationary - polar solid
mobile - non polar solvent

separation - due to varying polarities, components interact with the stationary phase to different extents.

Question 14

advantages of HPLC

Answer 14

High sensitivity and precision
Small sample size
Readily automated

Question 15

disadvantages of HPLC

Answer 15

• Moderately expensive instrument
• Trained technician required to operate
• Substance must be soluble in a suitable solvent

Question 16

method of HPLC

Answer 16

• a sample is injected, mobile phase (non-polar solvent) and sample are pushed through the dense column under high pressure.
• different compounds have different retention times (Rt) (due to varying polarities and solubility’s)
• output can be detected by compounds absorbing UV
• can be connected to a mass spectrometer

Question 17

what is gas chromatography (GC) with its phases

Answer 17

used to identify individual substances and concentrations of small organic molecules that can withstand high temperatures

mobile - intert carrier gas
stationary phase - liquid

Question 18

separation of GC

Answer 18

separation depends on boiling point and solubility
- high BP = long retention time
- more solubility = long retention time

Question 19

advantages of GC

Answer 19

High sensitivity and precision
Small sample size
Readily automated

Question 20

disadvantages of GC

Answer 20

Moderately expensive instrument
Trained technician required to operate
Sample must be vapourised without breaking down.

Question 21

methods of GC

Answer 21

a very small amount of a sample is injected into the machine
the injector is contained in an oven
the sample boils and is carried along a thin column by an inert carrier gas
the time taken to travel through the tube will depend on how much time is spent moving with the gas rather than being attached to the liquid (solubility).
The retention time (Rt) is used to
identify each component.

Question 22

interpretation of chromatography

Answer 22

each compound in the mixture will produce a peak

the areas under the peaks are proportional to the amount of a compound

retention times are used to identify compounds – they are found out by putting known compounds through the system under similar conditions