Chromatography II

Question 1

Describe normal phase chromatography

Answer 1

Polar SP/Non-polar MP used

Non-polar analytes don’t interact with SP so elute faster, more polar do interact and separate well

Question 2

how does an increase in solvent polarity affect normal phase chromatography

Answer 2

Inc in solvent polarity inc solvent strength and dec retention (competition on adsorption sites on silica)

Question 3

When is the best retention and separation obtained?

Answer 3

Using non-polar solvents with low solvent strengths

Question 4

Describe reverse phase chromatography

Answer 4

Hydrophobic non-polar SP on surface of solid matrix and polar MP
Polar analytes not retained (elute quickly), non-polar interact with SP so retained/ separated on RP column

Question 5

Describe pH and RPC

Answer 5

If analyte neutral, pH of aq MP doesn’t affect separation

Question 6

What are the 4 classifications methods?

Answer 6

Adsorption, Partition, Ion exchange, Pore penetration

Question 7

Describe adsorption chromatography

Answer 7

Solid SP where samples adsorbed, Liquid/Gas MP

Compounds distribute btw 2 phases through sorption/desorption processes

Question 8

Describe partition chromatography

Answer 8

Liquid SP supported on inert solid, Liquid/Gas MP

Question 9

Describe what the column in column chromatography may look like

Answer 9

Column may be packed with small particles, coated with thin layer of liquid phase

Question 10

Describe ion exchange chromatography

Answer 10

Uses ion exchange resin as SP, separation based on ion exchange equilbria

Question 11

Describe size exclusion chromatography

Answer 11

Solvated molecules separated by size, depends on ability to penetrate sieve-like structure SP

Question 12

Describe thin layer chromatography (TLC)

Answer 12

SP - Thin layer on surface of plate, Samples in volatile solvent, evaporated, plate into tank with MP, closed, MP up by cap.ac

Question 13

Advantages of TLC

Answer 13

Inexpensive, Simple, Easy to detect analytes

Question 14

Disadvantages of TLC

Answer 14

More detection limits than HPLC/GC

Question 15

How to calculate Rf value?

Answer 15

Distance travelled by solute/Distance to solvent front

Question 16

What are the 2 types of TLC visualisations?

Answer 16

Physical - UV at 254nm

Chemical - I2, H2SO4, pH indicators, Ninhydrin for AA

Question 17

Describe how adjusting MP polarity affects Rf

Answer 17

Analytes with stronger interactions with SP have lower Rf values (non-polar)

Question 18

What are the main parts of an LC system?

Answer 18

Solvent delivery
Separation column
Detector

Question 19

Describe gas chromatography (GC)

Answer 19

Analytes separated btw MP/SP, MP (gas) under pressure flowing through heated column coated with SP (inner column), Column - long tube of silica/metal

Question 20

Which parameters control GC separation?

Answer 20

Temp of injector/column
Type/amount of SP
Column size
Type/speed of gas

Question 21

Describe temperature control of GC

Answer 21

Sample compounds with similar volatiles separated at same column temp

Question 22

What are the 3 different types of injection systems?

Answer 22

Split, Splitless, Cool on-column injection

Question 23

Describe split injection

Answer 23

Evaporated sample split so only small portion enters column (best for high conc of analytes)

Question 24

Describe splitless injection

Answer 24

Total sample volume injected into column

Question 25

Describe cool on-column injection

Answer 25

Direct injection to cold column, sample shouldn't have non-volatile solvents (may block column)

Question 26

Describe the SP desired product of GC

Answer 26

Low volatility, Thermally stable, Chemically inert, Forms thin film

Question 27

Describe the effect of flow rate in GC

Answer 27

Broader peak if gas speed is too low/high

Question 28

When is the highest efficiency achieved?

Answer 28

By optimum gas velocity

Question 29

Describe the effect of temperature and RT

Answer 29

Increase in temp by 30C halves RT

Question 30

What are the 2 types of GC columns?

Answer 30

Packed, Capillary

Question 31

Describe packed columns

Answer 31

Packed with particles, covered with SP | SP particles fill open tubes, leads to broader peaks

Question 32

Describe capillary columns

Answer 32

Metal of fused silica | Open tubes with little pressure drop so can use very long columns without inc in pressure

Question 33

Describe characteristics of the ideal detector

Answer 33

Good stability, sensitivity, short response time

Question 34

What are the most common GC detectors?

Answer 34

Mass spec detector | Flame ionisation detector