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Analytical chemistry > Capillary electrophoresis > Flashcards

Capillary electrophoresis Flashcards

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1
Q

Is CE chromatography?

A

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

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2
Q

What is electrophoresis?

A

Separation of charged analytes in an applied electric field

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3
Q

Why do ions move at different speed?

A

It depends on their charge and hydrodynamic radius (size)

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4
Q

What is a challenge in CE?

A

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

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5
Q

How can we minimise Joule heating?

A

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

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6
Q

What are the components of CE?

A

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

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7
Q

What are advantages of CE over HPLC?

A

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

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8
Q

What are disadvantages of CE over HPLC?

A

Stability issues
High detection limits
Limited selectivity

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8
Q

What is the most commonly used capillary material?

A

Fused silica

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9
Q

What is BGE?

A

Background electrolyte

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10
Q

What is EOF?

A

Electroosmotic flow

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11
Q

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

A

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

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12
Q

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

A

Yes

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13
Q

Where is the EOF moving?

A

Towards the cathode

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14
Q

What does the cross-sectional flow profile look like?

A

Flat unlike HPLC

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15
Q

How can you control the EOF?

A

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

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16
Q

What are the ions movements based on?

A

Charge and size

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17
Q

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

A

Move more

18
Q

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

A

Move less

19
Q

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

A

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

20
Q

How can we improve separation efficiency in CE?

A

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

21
Q

How do we minimise Joule heating?

A

Low voltage
Narrow capillary
Thermostating

22
Q

What type of detector is used in CE?

A

UV-Vis

23
Q

What does electrodispersion lead to?

A

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

24
Q

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

A

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

25
Q

Is there any selectivity and retentivity in CE?

A

No. There is no distribution between phases

26
Q

Which different injection modes exist?

A

Hydrodynamic and electrokinetic (remember lab)

27
Q

Where is the detector located in CE?

A

On-column detection

28
Q

What is tM?

A

Migration time

29
Q

What is teo?

A

Time of electroosmotic flow

30
Q

What is the “diagram” called?

A

Electropherogram

31
Q

What is CE about in short?

A

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

32
Q

What is the most important parameter to control?

A

pH

33
Q

What makes the EOF move?

A

The charged capillary wall surface

34
Q

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

A

Yes

35
Q

How can you do chiral separation using CE?

A

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

36
Q

What is CZE?

A

Capillary zone electrophoresis (the simplest form)

37
Q

What is MEKC?

A

Capillary electrokinetic chromatography

(Micelles, separation based on hydrophobic effect)

38
Q

How does MEKC work?

A

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

39
Q

What do you use MEKC for?

A

Amino acids, nucleotides, pharmaceuticals, vitamin

40
Q

What are the surfactants used for in MEKC?

A

To create a pseudo-stationary phase (micelles)

41
Q

What is CEC?

A

Capillary electrochromatography

42
Q

How much does Rs increase when you increase the voltage?

A

Increases with the square root of the applied voltage

43
Q
A

Analytical chemistry (9 decks)

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