Capillary electrophoresis

Question 1

Is CE chromatography?

Answer 1

No, even though it is about separation, chromatography is about separation based on distribution between two phases. In CE no stationary phase and no partitioning

Question 2

What is electrophoresis?

Answer 2

Separation of charged analytes in an applied electric field

Question 3

Why do ions move at different speed?

Answer 3

It depends on their charge and hydrodynamic radius (size)

Question 4

What is a challenge in CE?

Answer 4

Joule heating
Heat released from the current flowing through the tube, proportional to diameter of the tube and applied electric field. It causes a loss of resolution

Question 5

How can we minimise Joule heating?

Answer 5

Narrower tubes (but detectability goes down)
Less conducting buffer solutions
Cold temperatures (higher density of water in cold temp means less convection)

Question 6

What are the components of CE?

Answer 6

Empty fused silica capillaries
High voltage power supply
(cheap equipment)

Question 7

What are advantages of CE over HPLC?

Answer 7

High efficiency
Wide pH range
Low solvent consumption
Ability to study equilibria in solution

Question 8

What are disadvantages of CE over HPLC?

Answer 8

Stability issues
High detection limits
Limited selectivity

Question 8

What is the most commonly used capillary material?

Answer 8

Fused silica

Question 9

What is BGE?

Answer 9

Background electrolyte

Question 10

What is EOF?

Answer 10

Electroosmotic flow

Question 11

What is the wall/surface of the fused silica capillary like?

Answer 11

It has OH groups, when pH is higher than pKa the H+ leaves so negatively charged O- on wall and H+ in BGE

Question 12

Is the surface/wall negatively charged when pH is larger than pKa?

Answer 12

Yes

Question 13

Where is the EOF moving?

Answer 13

Towards the cathode

Question 14

What does the cross-sectional flow profile look like?

Answer 14

Flat unlike HPLC

Question 15

How can you control the EOF?

Answer 15

Temperature, electric field, buffer pH, ionic strength of buffer

Question 16

What are the ions movements based on?

Answer 16

Charge and size

Question 17

Will analytes move more or less if the charge is more?

Answer 17

Move more

Question 18

Will analytes move more or less if the size is large?

Answer 18

Move less

Question 19

Is there an A, B or C term in the Van Deemter curve for CE?

Answer 19

Only B term. Only longitudinal diffusion. No resistance to mass transfer and no multiple flow paths.

Question 20

How can we improve separation efficiency in CE?

Answer 20

Alter pH to increase analyte mobility
Reduce temperature to decrease diffusion
Increase separation voltage

Question 21

How do we minimise Joule heating?

Answer 21

Low voltage
Narrow capillary
Thermostating

Question 22

What type of detector is used in CE?

Answer 22

UV-Vis

Question 23

What does electrodispersion lead to?

Answer 23

Fronting and tailing, caused by differences in conductivity and mobility in the sample zone and in the buffer

Question 24

Separation in CE is primarily driven by _____ instead of selectivity like chromatography

Answer 24

Efficiency (the term containing N in Rs = efficiency * selectivity * retentivity)

Question 25

Is there any selectivity and retentivity in CE?

Answer 25

No. There is no distribution between phases

Question 26

Which different injection modes exist?

Answer 26

Hydrodynamic and electrokinetic (remember lab)

Question 27

Where is the detector located in CE?

Answer 27

On-column detection

Question 28

What is tM?

Answer 28

Migration time

Question 29

What is teo?

Answer 29

Time of electroosmotic flow

Question 30

What is the "diagram" called?

Answer 30

Electropherogram

Question 31

What is CE about in short?

Answer 31

Separation of ionic compounds in an electric field inside a narrow capillary

Question 32

What is the most important parameter to control?

Answer 32

pH

Question 33

What makes the EOF move?

Answer 33

The charged capillary wall surface

Question 34

Can you do CZE (capillary zone electrophoresis) both in positive and negative mode?

Answer 34

Yes

Question 35

How can you do chiral separation using CE?

Answer 35

Using cyclodextrins the enantiomers will bind differently which allows them to be separated

Question 36

What is CZE?

Answer 36

Capillary zone electrophoresis (the simplest form)

Question 37

What is MEKC?

Answer 37

Capillary electrokinetic chromatography (Micelles, separation based on hydrophobic effect)

Question 38

How does MEKC work?

Answer 38

Analytes partition between BGE and micelles based on hydrophobic effects and ion pairing

Question 39

What do you use MEKC for?

Answer 39

Amino acids, nucleotides, pharmaceuticals, vitamin

Question 40

What are the surfactants used for in MEKC?

Answer 40

To create a pseudo-stationary phase (micelles)

Question 41

What is CEC?

Answer 41

Capillary electrochromatography

Question 42

How much does Rs increase when you increase the voltage?

Answer 42

Increases with the square root of the applied voltage