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CHM 326 > Seperation & GCS > Flashcards

Seperation & GCS Flashcards

1
Q

What is analytical separation?

A

Operation (process) in which a mixture is divided into at-least 2 components with different compositions OR 2 molecules with the same chemical structure but with different stereochemical structure

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2
Q

What are the two types if analytical separation?

A

Chemical and Physical

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3
Q

What is chemical separation based on?

A

Based on the differences in chemical reactivity

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4
Q

What is physical separation based on?

A

Based on differences in physical properties

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5
Q

What does the partition coefficient (k) represent?

A

The degree of separation

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6
Q

What does Q represent in separations?

A

The remaining fraction of solute in the water equilibrium

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7
Q

What type of separation process is extraction?

A

Equilibrium separation process

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8
Q

List the different equilibrium separation processes

A
  1. Precipitation
  2. Fractional crystallization
  3. Fractional distillation
  4. Extraction
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9
Q

What is Chromatography?

A

A physical method of separation in which components to be separated are distributed between two phases

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10
Q

What are the phases in chrmatography?

A
  1. mobile phase

2. stationary phase

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11
Q

Explain the difference between the mobile phase and the stationary phase in chromatography

A

The stationary phase does not move whereas the mobile phase moves through the stationary phase

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12
Q

List all of the chromatograph components in order of flow

A
  1. mobile phase supple reservoir
  2. mobile phase delivery system
  3. sample injection system
  4. column packed with stationary phase
  5. detection system
  6. mobile phase waste reservoir
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13
Q

What is the mobile phase supply reservoir in GCS vs. HPLC?

A

It is an inert carrier in GCS and liquid in HPLC

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14
Q

What is the mobile phase delivery system in GCS vs. HPLC?

A

High or low pressure liquid pump in HPLC and pressurized gas tank in GCS

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15
Q

What is the detection system in a chromatograph dependent on?

A

Dependent on the nature of samples

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16
Q

List the types of retention by sorption

A
  1. Adsorption [SiO2 (silica) stationary phase]

2. Partition [GC with liquid stationary phase]

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17
Q

What occurs in adsorption [SiO2 (silica) stationary phase]?

A

Adsorption of solutes occurs at the interface (where mobile and stationary phase meet) between the phases

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18
Q

What occurs in partition [GC with liquid stationary phase]?

A

Sample components partition between the mobile phase and the supported liquid layer (stationary phase)

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19
Q

What is a type of retention by exclusion and what are the two different analytical techniques that it can be performed with?

A

Size exclusion (gel filtration or gel permeation)

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20
Q

Which solutes show less retention in retention by exclusion (aka size exclusion)?

A

Larger sized solutes show less retention than smaller

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21
Q

How is retention by exclusion driven?

A

It is entropically driven

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22
Q

What does Delta H equal in retention by exclusion?

A

It equal 0

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23
Q

How does retention by ion-exchange occur?

A

The advancing front of stronger acid B+ exchanges with weaker acid A+ pre-equilibrated with the basic resin

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24
Q

What is the stationary phase in retention by ion-exchange?

A

it is a sulfonated resin

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25
Q

What is the stationary phase in retention by exclusion?

A

it is porous

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26
Q

What is the stationary phase in partition retention by sorption?

A

GC with liquid stationary phase

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27
Q

What is the stationary phase in adsorption retention by sorption?

A

Silica

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28
Q

What are the three different methods of retention by affinity?

A
  1. A change of buffer composition elutes the bound substance w/o harming it or the ligand
  2. Extremes of pH or high [chaotropic agent] are required for elution, but may cause permanent or temporary damage
  3. Specific elution by addition of a substance that competes for binding
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29
Q

What is the benefit of retention by affinity using specific elution by addition of a substance that competes for binding?

A

it can enhance the specificity of media that use group-specific ligands

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30
Q

What are the two types of mass transport in an equilibrium separation process?

A
  1. Extraction

2. Chromatography

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31
Q

In separation, if the chemical reaction produces a negative delta G is the reaction spontaneous or not spontaneous?

A

it is spontaneous when delta G is negative

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32
Q

What happens if delta G is positive or 0 in a chemical reaction in separation?

A

There is no reaction

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33
Q

When will you see no partition of distribution of solute between two phases?

A

When delta G is positive or 0

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34
Q

When will partition of distribution of a solute be spontaneous?

A

When delta G is negeative

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35
Q

If k >1 what will delta G be and what does this mean?

A

delta G will be negative and the distribution between the phases will be spontaneous

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36
Q

if k=1 what will delta G be and what does this mean?

A

Delta G will equal 0 and no further separation will occur as the system is at equilibrium

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37
Q

if k<1 what will delta G be and what does this mean?

A

delta G will be positive and the separation will not proceed as it is not thermodynamically favorable

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38
Q

What is delta S?

A

the entropy of separation

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39
Q

What is delta H?

A

the enthalpy of separation

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40
Q

Why does adsorption of solutes occur at the interface between the phases?

A

Due to specific interactions between the solutes and stationary phase which produces a non-zero delta H due to dipole-dipole interactions and hydrogen bonding

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41
Q

What is enthalpy in regards to separation?

A

it is the change in numbers of micro-states

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42
Q

In regards to enthalpy in separation, why is delta H greater than delta S?

A

Because decreasing entropy takes energy giving off a larger magnitude of delta H ( bigger magnitude = more negative)

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43
Q

When is delta H negative in separation?

A

When the solute is retained

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44
Q

What is the sign of delta S when the solute is retained and why?

A

Positive because you lose entropy

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45
Q

When is the separation enthalpically driven?

A

When delta G is negative

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46
Q

When is separation entropically driven?

A

when delta H is equal to 0

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47
Q

What is void time?

A

solutes in enthalpically driven separation that don’t interact with the stationary phase elute at the void time

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48
Q

How is efficiency reached in separations?

A

by decreasing plate height to maximizing plate count (N)

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49
Q

What is mass transfer?

A

crossing at the interface

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50
Q

What is efficiency dependent on?

A

retention time and column length

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51
Q

What does a theoretical plate represent?

A

the amount of times equilibrium is met

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52
Q

Why do you need to run separation at relatively slow rates?

A

To keep equilibrium at each plate

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53
Q

Is the rate of mass transport or mass transfer greater at equilibrium along the column?

A

The rate of mass transfer is greater than mass transport

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54
Q

What is band width dependent on?

A

mass transport

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55
Q

What is “A” in the van deemter equation

A

It is a constant that is offset of the Y-axis

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56
Q

What is “Cu (mu)” in the van deemter equation?

A

it is a linear function

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57
Q

what is mu in the van deemter equation?

A

The velocity of the mobile phase (aka flow rate)

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58
Q

What is “H” in the van deemter equation?

A

it is the plate height

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59
Q

What is the A term in the van deemter equation?

A

it is flow rate independent and due to different paths taken by the solute moving down the column (eddy diffusion)

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60
Q

What is Eddy Diffusion?

A

Different paths taken by the solute moving down the column

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61
Q

What is the B term in the van deemter equation?

A

It is flow rate dependent and relates to “longitudinal diffusion” along column length

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62
Q

What is the C term in the van deemter equation?

A

Relates to the rate of mass transfer

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63
Q

Which van deemter equation term is most complex?

A

The C term

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64
Q

Which van deemter equation term is called the “non-equilibrium” contribution to H?

A

The C term

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65
Q

What is a resolution an indicator of?

A

It is an indicator of separation

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66
Q

What is “df” in GCS?

A

the dimension of the film

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67
Q

What is the most common liquid stationary phase used in GCS?

A

Open tubular (WCOT)

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68
Q

What types of gas are used in GCS?

A

He, N2, & Ar

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69
Q

What is tR?

A

retention time

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70
Q

how is retention time and boiling point of an analyte related?

A

Retention time increases as the BP of an analyte increases

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71
Q

What exerts a strong influence on tR in GCS?

A

The polarity of the stationary phase

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72
Q

What is the operation principle for retention in GC based on?

A

Polarity, “like dissolves like”

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73
Q

What are four stationary phases used in GCS?

A
  1. Diphenyl/dimethyl polysiloxanes
  2. Cyanopropyl/phenyl/dimethyl polysiloxanes
  3. Carbowax (polyethlene glycol)
  4. Biscyanopropyl/cyanophenyl
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74
Q

What is the polarity for the corresponding GCS stationary phase?

  1. Diphenyl/dimethyl polysiloxanes
  2. Cyanopropyl/phenyl/dimethyl polysiloxanes
  3. Carbowax (polyethlene glycol)
  4. Biscyanopropyl/cyanophenyl
A
  1. NP
  2. intermediate polarity
  3. strongly polar
  4. strongly polar
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75
Q

True or False: As the particle size (dp) decreases, the efficiency of a GC separation which employs a wall-coated open tubular column (WCOT) decreases

A

False

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76
Q

True or False: When a separation is entropically-driven,

ΔG = -T∆S.

A

True

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77
Q

Name two of the “Big Three of Chromatography”

A

Retention, efficiency, & resolution

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78
Q

True or False: As the particle size (dp) increases, the efficiency of a GC separation which employs a packed column decreases.

A

True

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79
Q

True or False: When a separation is entropically-driven, ΔH ≠ 0.

A

False

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80
Q

True or False: For an open tubular GC column, such as wall-coated open tubular (WCOT) column, the van Deemter equation’s A term = 0.

A

True

81
Q

Explain why the value of the plate height, H, in the

van Deemter equation for GC is dominated by the magnitude of the B term.

A

Diffusion strongly influences plate height, H, in GC.
Because DM is large, B is large.
As a result, plate height, H, in GC is said to be “B term-driven”.

82
Q

What are the six advantages of GC?

A
  1. rapid analysis times
  2. Highly resolved peaks
  3. both qualitative and quantitative
  4. sensitive
  5. Micro-scale sample size
  6. simple and relatively inexpensive instrumentation
83
Q

What are the three limitations of GC?

A
  1. samples must be volatile
  2. samples must be temperature-stable
  3. Large-scale separations are not always feasible
84
Q

In WCOT, what is the A term equal to?

A

0

85
Q

In WCOT, what is the B term equal to?

A

2Dm

86
Q

In WCOT, what is the C term equal to?

A

[8k’df^2/(1+k’)^2Ds]

87
Q

For a WCOT, what is the van deemter equation?

A

H=B/u + Cu

88
Q

What does the term D stand for in the fick equation?

A

diffusion coefficient

89
Q

As temperature increases what happen to D?

A

D increaases

90
Q

When two gases or liquids are separated into two compartments, what is dc/dx?

A

dc/dx>0

91
Q

When two gases or liquids are in one compartment, what is dc/dx?

A

dc/dx=0

92
Q

Is diffusion of gases or liquids faster and by what order of magnitude?

A

Diffusion of gas is fast by 4 magnitudes

93
Q

True of false: diffusion influences plate height in GC?

A

True

94
Q

A dp decreases, what occurs to A?

A

it decreases

95
Q

What needs to occur to dp to decrease H?

A

need to minimize dp

96
Q

As Dm decreases, what occurs to B?

A

it decreases

97
Q

To decrease H what must occur to Dm?

A

Dm must be minimized

98
Q

What is the magnitude of Dm in the B term in GC?

A

10^-1 cm^2/s

99
Q

In the C term in GC, which term is negligible?

A

The second term

100
Q

What occurs to C as df decreases?

A

C decreases

101
Q

AS temperature increases in GC, what occurs to tR, Rs, and H?

A

tR decreases
Rs decreases
H increases

102
Q

What occurs at every 30C increase in temperature?

A

it halves tR

103
Q

In the B term, as temperature increases, what happens to Dm?

A

Dm increases

104
Q

in the C term, as temperature increases, what occurs to Ds?

A

Ds increases

105
Q

In the B and C term in GC, is Dm or Ds greater?

A

Dm»Ds

106
Q

How is retention time and overlapping peaks resolved in GC?

A

via the use of temperature programming

107
Q

What does it mean if a compound is combustible?

A

carbon-containing compound

108
Q

which GC detector requires combustible separated compounds?

A

FID

109
Q

What is an excellent detector for quantitative analysis of separated compounds?

A

FID

110
Q

How does FID work?

A

separated compounds are injected into a hydrogen-oxygen flame and combusted

111
Q

In FID what is produced and what does it generate?

A

Ions are produced which generate an ion current

112
Q

What is and ion current?

A

A signal

113
Q

What does TCD stand for?

A

Thermal conductivity detector

114
Q

What is a universal detector in GC?

A

Thermal conductivity detector

115
Q

What must a TCD detector use?

A

it must use a mobile phase of high thermal conductivity

116
Q

What is an example of a mobile phase with high thermal conductivity?

A

He

117
Q

How does a TCD work?

A

the difference in thermal conductivity between the mobile phase and separated compounds produces a signal proportional to the concentration of the separated compound

118
Q

What does ECD stand for?

A

Electron capture detector

119
Q

What are beta particles?

A

electrons

120
Q

What detector is extremely sensitive to halogenated compounds?

A

ECD

121
Q

What atoms are highly electronegative?

A

halogens

122
Q

What is used in ECD and what does it do?

A

it uses a radionuclide as a source of beta particles which shower the stream of separated compounds

123
Q

How does ECD work?

A

Separated compounds containing highly electronegative atoms capture beta particles and produce a signal proportional to the compound’s concentration

124
Q

What are the seven advantages of HPLC compared to GC?

A
  1. volatile samples not required
  2. thermal stability not required
  3. easier sample recovery after separation low temperature operation
  4. mobile phase composition can be varied systematically during the separation
  5. wider range of stationary phase
  6. wider range of applicable detectors
  7. mobile phase and stationary phase participate in the separation leading to greater selectivity in the separation
125
Q

What occurs in a gradient elution in HPLC?

A

the mobile phase composition is varied systematically during the separation

126
Q

What are considered LC methods in HPLC?

A

all chromatographic. methods which employ a liquid mobile phase

127
Q

What is the critical distinction between HPLC and GC?

A

the mobile phase

128
Q

What are the components of a high performance liquid chromatograph in order of flow?

A
  1. solvent reservoir (s) and degasser
  2. pumping system and gradient mixer
  3. sample injection system
  4. HPLC column
  5. detector
  6. waste reservoir
129
Q

What is the chemical nature of the solvent reservoir and degasser in HPLC?

A

aqueous and non-aqueous

130
Q

What are five types of column used in HPLC?

A

1, reverse phase

  1. normal phase
  2. ion exchange
  3. ion exclusion
131
Q

what are three detectors that can be used in HPLC?

A
  1. spectroscopic
  2. refractive index
  3. conductivity
132
Q

what is longitudinal diffusion in HPLC?

A

molecular diffusion of solute along the length of the column

133
Q

What is the van deemter equation in HPLC?

A

H=A + B/u + Cmu + Csmu + Csu

134
Q

In HPLC, what is the Cs term in the van deemter equation?

A

stationary phase mass transfer

135
Q

In HPLC, what is the Cm term in the van deemter equation?

A

mobile phase mass transfer of solute in flow streams between particles

136
Q

In HPLC, what is the term Csm in the van deemter equation?

A

stagnant mobile phase mass transfer of solute between the flow steam and stagnant pools of mobile phase

137
Q

What is stationary phase mass transfer in HPLC?

A

diffusion of solute between mobile and stationary phases

138
Q

In mobile phase mass transfer (Cm) in HPLC, where is the solute?

A

the solute is in laminar flow streams between particles

139
Q

in the Cm term, what is Dm equal to in HPLC?

A

~10^-4

140
Q

What is stagnant mobile phase mass transfer (Csm) in HPLC?

A

diffusion of solute between moving and stagnant pools of mobile phase

141
Q

In the term Csm, what is Dm equal to in HPLC?

A

~10^-4

142
Q

What is stationary phase mass transfer (Cs) in HPLC?

A

diffusion of solute between mobile and stationary phases

143
Q

In the Cs term, what is Ds equal to in HPLC?

A

~10^-5

144
Q

In HPLC, what is Ds?

A

diffusion coefficient in the stationary phase

145
Q

What is DI in HPLC?

A

the diffusion coefficient in the liquid phase (stationary phase)

146
Q

What is Dm in HPLC?

A

the diffusion coefficient in the mobile phase (liquid)

147
Q

What is referred to as “C-term driven”?

A

HPLC

148
Q

What occurs to A as dp decreases in HPLC?

A

A decreases

149
Q

What must occur to dp to decrease H in HPLC?

A

must minimize dp

150
Q

What occurs to Dm as B decreases in HPLC?

A

Dm decreases

151
Q

In HPLC, which term is very small and why?

A

The B term is very small in HPLC because Dm is small

152
Q

In HPLC, what is the magnitude of Dm?

A

10^-4 to 10^-5

153
Q

In HPLC, what is the magnitude of the Cs term?

A

10^-5 to -6

154
Q

In HPLC, what is the magnitude of the Csm term?

A

10^-4 to -5

155
Q

In HPLC, what is the magnitude of the Cm term?

A

10^-4 to -5

156
Q

In HPLC, as df and dp decreases, what occurs to the C term?

A

The C term decreases

157
Q

In HPLC, what occurs to the C term as Ds and Dm decreases?

A

The C term increases

158
Q

in HPLC, what must occur in the C term to decrease H?

A

df and dp must be minimized while maximizing Ds and Dm

159
Q

What are the three components of the reverse phase column in HPLC?

A
  1. solid support
  2. C-X chain
  3. “end cap”
160
Q

In Reverse phase HPLC, what can the solid support of the column be made of?

A
  1. rigid (silica)
  2. hard gels (polymer)
  3. macro-porous
  4. spherical
  5. non-spherical
161
Q

What must dp be equal to in the solid support of reverse phase HPLC?

A

dp must be less than or equal to 10 um

162
Q

In reverse phase HPLC what is the end cap made up of?

A

trimethylsilane group [-Si(CH3)3]

163
Q

In reverse phase HPLC, what can the C-X chain be made up of?

A
  1. C-8 (octyl)
  2. C-18 (octadecyl)
  3. phenyl
  4. cyano-propyl
164
Q

What occurs to the solid support surface in reverse phase HPLC?

A

silanization of the solid support surface

165
Q

In silanization of the solid support surface in reverse phase HPLC, what reaction takes place?

A

-Si-OH + Cl-Si(R)3 to -Si-O-Si(R)3 + HCl

166
Q

In silanization of the solid support surface in reverse phase HPLC, what can the R term be?

A

H or (1, 2, 3) alkly or aryl group

167
Q

What are the three components in reverse phase HPLC?

A
  1. Mobile phase
  2. Stationary phase
  3. Solid support
168
Q

What is the polarity of the stationary phase in reverse phase HPLC?

A

It is non-polar

169
Q

What does the term k’ stand for?

A

retention

170
Q

In reverse phase HPLC, what is retention (k’) determined by?

A

it is determined by non-specific hydrophobic interactions between the stationary phase and the solute

171
Q

What does the term alpha stand for in reverse phase HPLC?

A

Selectivity

172
Q

In reverse phase HPLC, what is selectivity determined by?

A

it is determined by the specific interactions between the mobile phase and the solute

173
Q

What is retention time (capacity factor) determined by in reverse phase HPLC?

A

it is determined by the solvent strength of the mobile phase (S)

174
Q

In reverse phase HPLC, how can the solvent strength of the mobile phase be controlled?

A

it can be controlled by mixing solvent of different polarity

175
Q

What is a common non-polar solvent used in reverse phase HPLC?

A

tetrahydrofuran

176
Q

what is meant by the term isocratic elution in HPLC?

A

when the mobile phase composition (its solvent strength) is held constant

177
Q

What is meant by the term gradient elution in reverse phase HPLC?

A

when the mobile phase composition is continuously changing during separation

178
Q

In reverse phase HPLC, what occurs as the slope of the gradient increases?

A

tR and Rs decreases

179
Q

What is meant by the term separation in HPLC and GC?

A

the selectivity

180
Q

What does the term Vr and Vm stand for?

A 
Vr = peak elution volume of solute
Vm = elution volume of the mobile phase
181
Q

what is the void volume in HPLC?

A

elution volume of the mobile phase (Vm)

182
Q

What is efficiency determined by?

A

plate count (N) and plate height (H)

183
Q

What does Rs stand for?

A

resolution

184
Q

Retention in HPLC is often expressed in terms of what?

A

expressed in terms of volume and time

185
Q

What does the term F stand for in HPLC?

A

the volumetric flow rate in mL/min

186
Q

What does IEC stand for?

A

ion exchange chromatography

187
Q

What are the components in an ion exchange chromatograph in order of flow?

A
  1. solvent reservoirs (A & B)
  2. pump/mixer
  3. injector
  4. IEC column
  5. detector
  6. waste reservoir
188
Q

What can be used as a mobile phase in IEC?

A

aqueous and non-aqueous modified solutions

189
Q

What can the elution in IEC be?

A
  1. isocratic

2. gradient

190
Q

What types of exchange modes does IEC function in?

A

both anion and cation exchange modes

191
Q

What does the term X^(+ or -) refer to in IEC?

A

the charged site on the ion exchange resin

192
Q

What forms do cation and anion exchange resins come in, in IEC?

A

both strong and weak forms

193
Q

What do strong anion exchangers employ as the charged sites on the resin in IEC?

A

they employ quaternary amine groups as the charged site on the resin

194
Q

What do weak anion exchangers employ as the charged sites on the resin in IEC?

A

They employ diethyl-amino groups as the charged sites on the resin

195
Q

What do strong cation exchangers employ as the charged sites on the resin in IEC?

A

they employ sulfonic acid groups

196
Q

What do weak cation exchangers employ as the charged sites on the resin in IEC?

A

they employ carboxymethyl groups

197
Q

Describe briefly the similarities and differences between mass transport and mass transfer in a chromatographic separation

A

Mass transport in a chromatographic separation is the movement of molecules through the stationary and mobile phases

Mass transfer in a chromatographic separation is the movement of molecules across the interface between the stationary and mobile phase

198
Q

Explain briefly what is meant by an entropically-driven chromatographic separation. Name one example of an entropically-driven chromatographic separation

A

In an entropically-driven separation the enthalpy of separation, delta H, = 0; delta G=delta H -T delta S, due to the lack of interactions between the solute and the stationary phase. Therefore delta G = - T delta S for the separation

An example of this is size exclusion separation

199
Q

Explain briefly what is meant by an enthalpically-driven chromatographic separation. Name one example of an enthalpically-driven chromatographic separation

A

The enthalpy of separation, delta H does not equal 0; delta G = delta H - t delta S, due to interactions between the solute and the stationary phase. delta G = delta H - T delta S for the separation but since delta H is much greater than delta S, delta G is driven by delta H

Examples include: sorption ( adsorption, partition), ion-exchange, affinity separations

CHM 326 (1 decks)

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