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CHM 343 Separations > FInal: Supercritical Fluid Chromatography & Capillary Electrophoresis > Flashcards

FInal: Supercritical Fluid Chromatography & Capillary Electrophoresis Flashcards

1
Q

What are the properties of a supercritical fluid?

A
  • the viscosity is similar to that of a gas
  • supercritical fluid can move through a capillary or packed column without high pressures needed in HPLC
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2
Q

What kind of gradient is used in supercritical fluid chromatography?

A

a gradient with increasing pressure in order to achieve increasing solvent density which therefore increases the eluent strength.

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3
Q

Why are relative eluent strengths of solvents in adsorption chromatography fairly indpendent of solute?

A

because they are both competing for adsorption sites therefore it doesn’t matter how strong the solvent is in comparison with the solute.

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4
Q

the density of a supercritical fluid is close to that of a (solid/liquid/gas).

A

liquid

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5
Q

is a supercritical fluid a good solvent or a bad solvent?

A

good solvent

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6
Q

supercritical fluids behaves more like the _______ mobile phase in _____ than the ______ mobile phase in ________.

A

liquid; HPLC

gaseous; GC

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7
Q

How do you recover supercritical fluid samples?

A

allow the solution to equilibriate with the atomosphere at relatively low temperature.

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8
Q

What is supercritical fluid chromatography?

A

a hybrid of gas and liquid chromatography, using supercritical fluid as its mobile phase.

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9
Q

What type of compunds can SFC handle?

A
  • nonvolatile or thermally unstable compounds
  • compunds with no spectroscopic or electrochemical properties
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10
Q

When would you choose to use SFC over GC?

A

when dealing with compounds that are nonvolatile or thermally unstable.

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11
Q

when would you choose to use SFC over LC?

A

when dealing with a compound with no spectroscopic or electrochemical properties.

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12
Q

In hydrophilic interaction chromatography (HILIC), why is eluet strength increased by increasing the fraction of water in the mobile phase?

A

since the stationary phase is polar, increasing the fraction of water in the mobile phase will allow it to compete better with the stationary phase therefore decresing the eluent time.

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13
Q

Why is high pressure needed in HPLC?

A

it increases the flow rate, which allows the eluates to come out faster and obtain more effective separation between peaks.

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14
Q

what is a bonded phase in liquid chromatography?

A

a liquid stationary phase is bonded to the solid support.

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15
Q

What are criteria for an adequate isocratic chromotographic separation?

A

adequate separation in a resonable time (0.5~20)

and Rs > 1.5

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16
Q

What are the general steps in developing an isocratic separation for reversed-phase chromatography with one organic solvent

A

1) Goal of analysis
2) Sample Preparation
3) Detector
4) wide gradient used to determine if isocratic or gradient separation is to be used.

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17
Q

what is electrophoresis?

A

a separation method based on the differential rate of migration ions in an applied dc electric field

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18
Q

Define Electrophoretic Migration.

A

The movement of ions is caused by the electric field , or the potential difference between two electrodes

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19
Q

Name the direction in which cations, anions, and neutral molecules migrate.

A

cations mgrate towards the cathode

anions migrate toward the anode

neutral molecules do not favor either

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20
Q

In electrophoretic migration, what does the rate at which the molecules move depend on?

A

charge-to-size ratios

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21
Q

the (smaller/larger) the ratio, the faster an ion migrates in the electric field.

A

larger

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22
Q

List all the variables for controlling electroosmotic flow.

(8 variables)

A
  1. Electric Field
  2. Ionic Strength
  3. Organic Modifiers
  4. Surfactant
  5. Temperature
  6. Buffer pH
  7. Covalent Coating
  8. Neutral Hydrophilic

EF, IS, OM, S, T, B, CC, NH

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23
Q

What is the result of changing the Electric Field variable in Electroosmotic Flow.

A

proportional change in EOF.

*joule heating may result*

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24
Q

What is the result of changing the Buffer pH variable in Electroosmotic Flow.

A

EOF decreases at low pH, increases at high pH.

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25
Q

What is the result of changing the Ionic Strength variable in Electroosmotic Flow.

A

Decreases the zeta potential between the cation layers and EOF with increasing buffer concentration

*high ionic strength means high current and Joule heating*

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26
Q

What is the result of changing the Organic Modifiers variable in Electroosmotic Flow.

A

increasing modifier decreases the zeta potential & EOF

*complex effects*

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27
Q

What is the result of changing the Surfactant variable in Electroosmotic Flow.

A

Adsorbs to capillary wall through hydrophobic or ionic interactions.

*Anionic surfactants increase EOF*

*Cationic surfactants decrease EOF*

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28
Q

What is the result of changing the Neutral Hydrophillic variable in Electroosmotic Flow.

A

Adsorbs to capillary wall via hydrophobic interactions.

*Decreases EOF by shielding surface charge, also increases viscosity*

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29
Q

What is the result of changing the Covalent Coating variable in Electroosmotic Flow.

A

chemically bonded to capillary wall

*Many things can happen*

30
Q

What is the result of changing the Temperature variable in Electroosmotic Flow.

A

changes the viscosity

*easy to control*

31
Q

What variable(s) of the Van Deemter equation apply to capillary electrophoresis. why don’t some of the variables apply?

A

Only the B term

A(multiple path) term does not apply becasue its an open tube

C (mass transfer) doesn’t apply because there is no stationary phase

32
Q

Where is the detector placed in CE?

A

at the cathode

33
Q

What is the difference between HPLC and CE?

A
  • CE has a flat flow vs HPLC has parabolic flow
  • CE has higher separation efficiency than HPLC
  • CE is simpler to operate than HPLC
  • HPLC has more mobile and stationary phase choices
  • CE is limited to thin capillaries while HPLC has variety.
34
Q

Name the two types of systems in CE.

A
  • Continuous system
  • Discontinuous system
35
Q

Name the different methods for continuous system electrophoresis.

A
  1. CZE: Caillary Zone Electrophoresis
  2. CEC: Capillary ElectroChromatography
  3. MEKC: Micellar Electrokinetic Capillary Chromat.
  4. CGE: Capillary Gel Electrophoresis
  5. CIEF: Capillary Isoelectric Focusing
36
Q

Name the method for discontinuous system electrophoresis.

A

CITP: Capillary Isotachophoresis

37
Q

What are the applications of CE

A
  • Analysis of carbohydrates
  • Analysis of inorganic anions/metals ions
  • DNA profiling
  • Protein identification
38
Q

Describe Lab-on-a-Chip.

A

liquid can now be moved by Electroosmosis or by pressure through micron-size channels etched into glass or plastic chips the size of a microscope slide.

39
Q

what are the different substrate materials for Lab-on-a-Chip.

A

silica

polymer

40
Q

Name the different types of detection methods for Lab-on-a-chip.

A

Fluorescence

Electrochemistry

Mass Spectrometry

41
Q

Although similar to HPLC, what are the distinguishable parts in supercritical fluid chromatography

A
  • A thermostatted column
  • A restrictor or back-pressure device
42
Q

what is the purpose of a thermostatted column oven in super critical fluid chrom.

A

to provide precise temperature control of the mobile phase

43
Q

what is the purpose of a restrictor or back-pressure device in super critical fluid chrom.

A

to maintain the desired temperature in the column and to convert the eluent from a super critical fluid to a gas for transfer to the detector

44
Q

What are the variables for super critical fluid chromatography?

A
  • pressure
  • temperature
45
Q

What is the most widely used mobile phase for supercritical fluid chromatography?

A

CO2

46
Q

Why is CO2 the most widely used mobile phase in supercritical fluid chromatography.

A
  • low critical temperature and pressureso its easily achieved and maintained.
  • great solvent for non-polar organic molecules
  • no absorbance in UV range
  • odorless and nontoxic
  • inexpensive
47
Q

What dectors are used for supercritical fluid chromatography.

A

can use standard GC or HPLC detectors

48
Q

what is one major advantage of SFC over HPLC?

A

flame ionization dectector can be used.

49
Q

What are some applications of supercritical fluid chromatography.

A
  • natural products
  • drugs(chiral separation)
  • foods
  • pesticides and herbicides
  • surfactants
  • fossil fuels
  • polymers
  • explosives and propellants
50
Q

list separation effciency of SFC, LC, and GC in order or greatest to least.

A

GC > SFC > LC

51
Q

What are the features of an ideal extraction for supercritical fluids.

A
  • rapid, simple, and inexpensive
  • quantitative recovery without loss or degration
  • yields a sufficiently concentrated solution of the analyte
  • very little laboratory waste.
52
Q

What is the reality of extraction for supercritical fluids.

A
  • requires longer time to achieve enough analyte
  • concentration step in required
  • solvent cost is high
  • degration and atmospheric pollution may occur.
53
Q

Name the components that make up the instrumentation for supercritical flluid extraction

A
  • A fluid source (CO2)
  • A syringe pump (>400 atm; 2ml/min)
  • A control valve
  • An exit valve
54
Q

What is the purpose of the separator and suppressor in suppressed-ion chromatography. For cation chromatography, why is the suppressor an anion-exchange membrane?

A

separator column: separates ions by ion exchange

suppressor column: reduces the conductivity of eluent by exchanging the counterion

the suppressor is anion exchange membrane in order to exchange an ion for OH-

55
Q

State the effects of increasing cross-linking on an ion-exchange column.

A

decreased swelling, increased exchange capacity and selectivity, but longer equilibration time.

56
Q

what is electroosmosis?

A

a pumping action where the excess cations in the diffuse part of the double layer migrates toward the cathode.

57
Q

State three different methods to reduce electroosmotic flow.

A
  1. Lowering the pH
  2. varying tho ionic strength
  3. Increase the Modifier
58
Q

Explain how neutral molecules can be separated by micellar electrokinetic chromatography

A

neutral molecules spends some time in the negativley charged micelles that are moving upstream with some electrophorectic velocity, and each neutral molecule has a different partition coefficent between the solution and the micelles which then means they can be thought of as a type of chromatography, because molecules will elute at different times.

59
Q

what are the two parts distingishable in super critical fluid chromatography?

A
  • Thermostatted column oven
  • A restrictor or back pressure device
60
Q

What does a thermostatted column oven provide in the supercritical fluid chromatography instrument

A

provides precise temperature control of the mobile phase

61
Q

What does a restrictor or back-pressure device provide in the supercritical fluid chromatography instrument

A

maintains the desired temperature in the column and converts the eluent froma supercritical fluid to a gas for transfer to the detector

62
Q

what is electrophoretic mobility (µep)

A

the constant of proportionality between the speed of the ion and the electric field strength

63
Q

What is the best method to control electroosmotic flow?

A

Change the buffer pH

64
Q

for molecules of similar size, mobilty (increases/decreases) with charge.

A

increases

65
Q

what is joule heating?

A

when the flow of ions in the capillary generates heat

66
Q

true or false: electrophoresis transports anions in the opposite direction from electoosmosis.

A

true

67
Q

at neutral or high pH, why does electroosmosis transport anions to the cathode?

A

because electroosmosis is usually faster than electrophoresis, and electroosmosis is always moving toward the cathode.

68
Q

At low pH, electroosmosis is weak and anions may never reach the detector. If you want to separate anions at low pH, what must you do?

A

reverse the polarity to make the sample end negative and the detector positive

69
Q

The higher the apparent mobility, the (longer/shorter) the migration time.

A

shorter

70
Q
A

CHM 343 Separations (3 decks)

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