Fad - Hplc Phases

Front 1

What are the two modes of modern-day HPLC?

Back 1

1. Normal phase

2. Reversed phase

Front 2

What is the most common form of HPLC?

Back 2

Reversed-phase

Front 3

What are the phases in reversed-phase HPLC?

Back 3

1. Polar mobile phase

2. Hydrophobic stationary phase

Front 4

Name a common hydrophobic stationary phase

Back 4

Octadecylsilyl (ODS)

Front 5

What are the phases in normal phase HPLC?

Back 5

1. Non-polar mobile phase

2. Polar stationary phase

Front 6

In ion-exchance chromatography, what is the basis for separation?

Back 6

Separation based upon ion-exchanging with counter-ions and ionic interaction with bonde ionic group

Front 7

In size-exclusion chromatography, what is the basis for separation?

Back 7

Separation based upon analyte's molecular size and sieving action of the column packing

Front 8

Name two common mobile phases for NPC

Back 8

1. Hexane

2. Dichloromethane

Front 9

Name some common stationary phases in NPC

Back 9

1. Silica

2. Alumina

3. Amino-

4. Cyano-

5. Phenyl bonded phases

Front 10

What type of analytes is NPC useful for?

Back 10

Polar analytes

Front 11

What type of analytes is RPC useful for?

Back 11

Water-insoluble non-polar analytes

Front 12

Name two common polar mobile phases

Back 12

1. Methanol in water

2. Acetonitrile in water

Front 13

In RPC, do polar or non-polar analytes elute first?

Back 13

Polar analytes elute first

Front 14

How can ionic compounds be separated in RPC?

Back 14

Ion-pairing reagents or ion suppression (Heptanesulphonic acid)

Front 15

What is IEC used to separate?

Back 15

Ionic or ionizable analytes

Front 16

What is the stationary phase for IEC?

Back 16

Anionic (sulphonate) or cationic (quaternary ammonium) groups on polymeric materials or silica.

Front 17

What does the mobile phase in IEC consist of?

Back 17

Buffered solutions of different pH and ionic strength

Front 18

What are the three primary characteristics of HPLC mobile phases?

Back 18

1. Desirable physical properties

2. Strength

3. Selectivity

Front 19

Name eight desirable physical properties of a HPLC mobile phase

Back 19

1. High purity

2. Low cost

3. UV transparency

4. Non-corrosive

5. Low viscosity

6. Low toxicity

7. Non-flammable

8. Sample solubility

Front 20

What is the name of the scale used to characterise the strength of solvents?

Back 20

Hildebrand's scale

Front 21

How should solvents be treated before use?

Back 21

Filtered and degassed

Front 22

Name five common mobile phase modifiers and their use

Back 22

1. Buffers - stabilise pH of mobile phase under RP

2. Acidifiers - Suppress ionisation of acidic analytes under RP

3. Ionic strength - Control elution of ionic analyte under RP

4. Ion-pair reagents - Separation of ionic compounds under RP

5. Amine modifiers - Reduce tailing of basic analytes under RP

Front 23

Name three examples of mobile phase buffers

Back 23

1. Phosphate

2. Acetate

3. Citrate

Front 24

Name two examples of mobile phase acidifiers

Back 24

1. Phosphoric acid

2. Acetic acid

Front 25

What is commonly used to control the ionic strength of a solvent?

Back 25

NaCl

Front 26

What is a commonly used ion-pair reagent?

Back 26

Heptanesulphonate

Front 27

What is a common amine modifier?

Back 27

Triethylamine

Front 28

What is peak tailing, and what type of chromatography is it mainly a problem in?

Back 28

Assymetry of peaks - mainly a problem when separating amines using RP

Front 29

How is peak tailing caused?

Back 29

Interaction of polar amines with residual silanols on the RP column

Front 30

How do you work out the value of peak tailing on a chromatogram?

Back 30

Front 31

At what value does peak tailing become unacceptable?

Back 31

>2.0

Front 32

Name three methods of overcoming peak tailing

Back 32

1. Lower pH (<3)

2. Add amine modifier

3. Endcapping

Front 33

What is an issue that can arise when lowering pH to overcome peak tailing?

Back 33

Can result in stripping of silica column

Front 34

How does adding an amine modifier help overcome peak tailing? What is one drawback?

Back 34

Competes with the analyte for the silnaols, therefore reducing analyte-silanol interactions. Drawback - stinks of fish.

Front 35

What is endcapping, and how is it accomplished?

Back 35

Endcapping is the reduction of residual silanols by 'capping' them to make them substantially less polar. Accomplished by adding Trimethylchlorsilane / Hexamethyldisilazane.

Front 36

How effective is endcapping at reducing silanols?

Back 36

Reduces by 50%