chromatography

Question 1

how does TLC separate?

Answer 1

• stationary phase is polar/non-polar
• mobile phase is polar/non-polar
• components of mixture adsorb onto the stationary phase and desorb and dissolve in the mobile phase in different degrees
• distance travelled by the mixture components depends on the strength of the intermolecular forces between solute+mobile phase and solute+stationary phase
• polar/non polar components travel a smaller/greater distance

Question 2

how does gas chromatography separate?

Answer 2

GC allows separation of components based on their volatility
- high temperature of of injecting chamber vapourises the sample
- sample of gas is passed through thin tube packed with an inert substance (eg silica) coated in a viscous, non-volatile liquid
- inert gas carrier (helium) acts as the mobile phase and moves the gas sample through the chromatography column
- various gas sample components move through at different speeds as they interact with the stationary phase (NOT THE MOBILE PHASE) and separate based on their volatility and particle size
- gas chromatography works the best for separating gas mixtures that can be easily vapourised without decomposing (molar mass less than 300)

Question 3

retention time and area for GC

Answer 3

Rt: depends on the component’s boiling point/volatility. determines the identity of the component based on its polarity/volatility/particle size
area: concentration of the component, but must be calibrated with a set of standards at known concentration

USE THE SAME TEMPERATURE, COLUMN, CARRIER GAS, GAS FLOW RATE

Question 4

HPLC

Answer 4

1) sample/mixture to be separated is loaded into the column containing the stationary phase (tightly packed column of fine particles) is pumped through column with high pressure
2) components of mixture adsorb onto SP with different degrees and desorb and dissolve into MP with different degrees
3) interaction between sample/mixture components and SP/MP means that they move through column at different speeds, allowing separation of mixture
4) greater tendency to adsorb onto onto SP rather than dissolve in mobile liquid phase as it has stronger IMF with SP than MP, takes longer to elute from the column, Rt increases

Question 5

why is HPLC high pressure

Answer 5

small particle size of SP, large SA that allows greater interaction with the analytes in the mobile phase for more efficient separation
greatly reduces flow rate of solvent and mixture through column, so high pressure pump increases flow rate