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Analytical > CE > Flashcards

CE Flashcards

1
Q

CE Instrument

A
  1. Outlet
  2. Inlet
  3. sample
  4. power supply
  5. capillary
  6. detector and computer
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2
Q

CE vs LC

A
  • no eddy diffusion
  • flat velocity profile
  • higher efficiency and resolution
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3
Q

Controlling EOF

A
  1. pH

determines ionisation of silanols

  1. Coating
    - permanent

constant EOF

  • dynamic

reversible, and variable EOF

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4
Q

Electrophoretic Mobility and Velocity

A
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5
Q

apparent velocity

A
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6
Q

Electrophoretic mobility from times

A
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7
Q

EOF velocity

A
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8
Q

Co vs Counter EOF

A

co:

EOF and mobility aligned. Detected before EOF.

Counter:

EOF and mobility opposite. Detected after EOF

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9
Q

CZE Separation Media

A

Background Electrolyte

contains co and counter ions for EOF

and buffered

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10
Q

CZE separation

A

separates by electrophoretic mobility

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11
Q

CZE analytes

A

Ions

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12
Q

CZE disadvantages

A

Cannot separate neutral (migrate together)

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13
Q

Detection methods

A
  1. Photometric

direct or indirect

  1. Conductivity

differences in conductivity

  1. MS
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14
Q

Co ions for indirect

A
  1. strong absorbance
  2. mobility close to analytes average

phthalic acid, p-hydroxybenzoic, chromate

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15
Q

Why Buffer

A

reproducibility

smoother signal

tolerance to sample pH

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16
Q

Electromigration Dispersion

A

Occurs whe conductivity lower in BGE

analytes move faster in BGE

causes tailing or fronting

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17
Q

Minimise EMD

A
  1. maximise electrolyte concentration in BGE
  2. minimise injected analyte concentration
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18
Q

Poor sensitivity UV

A

Because of beers law

  1. short path length
    - bubble cell, right angle, multi reflection cell
  2. limited sample amounts

stack analyte

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19
Q

Field Enhancement Stacking

A

analyte has lower conductivity than BGE

analyte moves faster in band

and stacks at interface

allows for longer injection, high sample amounts, increased sensitivity

typically prepared in water

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20
Q

CE-MS

A

offline detection

Advantages:

  • high sensitivity
  • qualitative and quantitative

Disadvantages

  • expensive
  • limit BGE/buffer choice
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21
Q

Electrokinetic chromatography details

A
  • allows for separation of neutrals
  • charged micelles have own migration time
  • partition between BGE and micelles by hydrophobicity
  • analytes that partition more towards micelles migrate closer to micelles
  • analytes that partition more towards micelles migrate closer to EOF
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22
Q

EKC separation media

A

BGE and psuedo stationary phase/micelles

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23
Q

EKC retention calc

A

Normal and

Reverse

k = 1/(tr/tmc - 1)

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24
Q

Neutral effective velocity

A
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25
Q

Retention factors EKC

A

hydrophobicity of analyte

concentration of micelles

structure of micelles

pH

additives e.g. ion pair

26
Q

Chiral EKC separation media

A

chiral pseudo stationary phase

cyclodextrin

27
Q

chiral EKC Separation mechanism

A

effective velocity (retention and mobility)

28
Q

chiral EKC analytes

A

small or large organic enantiomers

29
Q

Chiral EKC Applications

A

purification

impurity determination

enantiomer excess

30
Q

chiral EKC advantages

A

Higher efficiency that LC

faster equilibration

cheaper

phased added to buffer rather than a column

can combine with other CE modes

31
Q

Enantiomer Excess

32
Q

Affinity Capillary Electrophoresis Details

A

Determination of binding constants of receptor and ligand

33
Q

ACE media

A

BGE with ligand or receptor

34
Q

ACE separation

A

ligand binds to receptor creating complex and altering migration time

increasing conc forms more complex and observed time is closer to complex time than receptor time

gradient of change is proportional to binding constant

35
Q

ACE limitations

A
  • time consuming
  • multiple experiments
  • specialised
  • assumptions (conc, equil, wall, field)
36
Q

ACE advantages

A
  • small sample size
  • binding stoichiometry
  • does need pure ligand
37
Q

ACE analytes

A

receptor and ligand

38
Q

Capillary Isotachopohoresis (cITP)

A

concentrates ions into bands

39
Q

cITP media

A

Leading and terminating electrolyte

40
Q

cITP separation

A

inject sample between LE and TE

LE > sample > TE

separates into mobility blocks

41
Q

cITP advantages

A

concentration of analyte blocks controlled by concentration of leading electrolyte

42
Q

cITP limits

A
  • conc changes affect migration times
  • hard to quantify
  • not good for analytical
43
Q

cITP analytes

44
Q

Capillary ioselectric focussing (cIEF)

A

separates zwitterions based on isoelectric point i.e. pH where no charge

45
Q

cIEF Media

A

anolyte catholyte

acid at the anode

base at the cathode

46
Q

cIEF Separation

A

anolyte/catholyte creates pH gradient

analytes migrate till reach isoelectric point

creates bands that can be eluted by pressure

47
Q

cIEF analytes

A

zwitterions/ampholytes

48
Q

cIEF applications

A

separating ampholytes

determining isoelectric point

49
Q

Capillary Gel Electrophoresis (CGE)

A

separate large molecules by size through seiving with gel

50
Q

CGE media

A

gel/soluble polymer

51
Q

CGE advantages

A

faster more efficient than traditional

replacable gel

automation

quantitation

52
Q

CGE applications

A

DNA sequencing

molecular weight determination

determination of agrregates

53
Q

Capillary Electrochromatography (CEC)

A

chromatographic phase/column embedded in capillary. Combines electrophoresis and chromatography

54
Q

CEC columns

A

packed

monolithic

open tubular

microfabricated

55
Q

CEC separation

A

effective mobility

(electrophoresis and retention)

56
Q

CEC advantages

A

can separate anions, cations and neutrals in one run

better efficiency than LC

57
Q

Stacking MEKC

A

sweeping

sample prepared without micelles

analyte migrates to interface of band and BGE

leading to sharper peaks

58
Q

oxidation at anode

A

2 H2O(l) → O2(g) + 4 H+(aq) + 4e−

becomes acidic

59
Q

Reduction at cathode

A

2 H+(aq) + 2e− → H2(g)

becomes basic

60
Q

uep units

A

cm2 / V min

61
Q

CZE method

A
  1. Know analytes
  2. choose BGE to ionise
  3. apply suitable voltage - avoid joule heating
  4. organic solvents - alter selectivity/solubility
  5. coatings - alter EOF

Analytical (7 decks)

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