Seperation & GCS Flashcards
(199 cards)
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
2
Q
What are the two types if analytical separation?
A
Chemical and Physical
3
Q
What is chemical separation based on?
A
Based on the differences in chemical reactivity
4
Q
What is physical separation based on?
A
Based on differences in physical properties
5
Q
What does the partition coefficient (k) represent?
A
The degree of separation
6
Q
What does Q represent in separations?
A
The remaining fraction of solute in the water equilibrium
7
Q
What type of separation process is extraction?
A
Equilibrium separation process
8
Q
List the different equilibrium separation processes
A
- Precipitation
- Fractional crystallization
- Fractional distillation
- Extraction
9
Q
What is Chromatography?
A
A physical method of separation in which components to be separated are distributed between two phases
10
Q
What are the phases in chrmatography?
A
- mobile phase
2. stationary phase
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
12
Q
List all of the chromatograph components in order of flow
A
- mobile phase supple reservoir
- mobile phase delivery system
- sample injection system
- column packed with stationary phase
- detection system
- mobile phase waste reservoir
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
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
15
Q
What is the detection system in a chromatograph dependent on?
A
Dependent on the nature of samples
16
Q
List the types of retention by sorption
A
- Adsorption [SiO2 (silica) stationary phase]
2. Partition [GC with liquid stationary phase]
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
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)
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)
20
Q
Which solutes show less retention in retention by exclusion (aka size exclusion)?
A
Larger sized solutes show less retention than smaller
21
Q
How is retention by exclusion driven?
A
It is entropically driven
22
Q
What does Delta H equal in retention by exclusion?
A
It equal 0
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
24
Q
What is the stationary phase in retention by ion-exchange?
A
it is a sulfonated resin
25
What is the stationary phase in retention by exclusion?
it is porous
26
What is the stationary phase in partition retention by sorption?
GC with liquid stationary phase
27
What is the stationary phase in adsorption retention by sorption?
Silica
28
What are the three different methods of retention by affinity?
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
29
What is the benefit of retention by affinity using specific elution by addition of a substance that competes for binding?
it can enhance the specificity of media that use group-specific ligands
30
What are the two types of mass transport in an equilibrium separation process?
1. Extraction
| 2. Chromatography
31
In separation, if the chemical reaction produces a negative delta G is the reaction spontaneous or not spontaneous?
it is spontaneous when delta G is negative
32
What happens if delta G is positive or 0 in a chemical reaction in separation?
There is no reaction
33
When will you see no partition of distribution of solute between two phases?
When delta G is positive or 0
34
When will partition of distribution of a solute be spontaneous?
When delta G is negeative
35
If k >1 what will delta G be and what does this mean?
delta G will be negative and the distribution between the phases will be spontaneous
36
if k=1 what will delta G be and what does this mean?
Delta G will equal 0 and no further separation will occur as the system is at equilibrium
37
if k<1 what will delta G be and what does this mean?
delta G will be positive and the separation will not proceed as it is not thermodynamically favorable
38
What is delta S?
the entropy of separation
39
What is delta H?
the enthalpy of separation
40
Why does adsorption of solutes occur at the interface between the phases?
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
41
What is enthalpy in regards to separation?
it is the change in numbers of micro-states
42
In regards to enthalpy in separation, why is delta H greater than delta S?
Because decreasing entropy takes energy giving off a larger magnitude of delta H ( bigger magnitude = more negative)
43
When is delta H negative in separation?
When the solute is retained
44
What is the sign of delta S when the solute is retained and why?
Positive because you lose entropy
45
When is the separation enthalpically driven?
When delta G is negative
46
When is separation entropically driven?
when delta H is equal to 0
47
What is void time?
solutes in enthalpically driven separation that don't interact with the stationary phase elute at the void time
48
How is efficiency reached in separations?
by decreasing plate height to maximizing plate count (N)
49
What is mass transfer?
crossing at the interface
50
What is efficiency dependent on?
retention time and column length
51
What does a theoretical plate represent?
the amount of times equilibrium is met
52
Why do you need to run separation at relatively slow rates?
To keep equilibrium at each plate
53
Is the rate of mass transport or mass transfer greater at equilibrium along the column?
The rate of mass transfer is greater than mass transport
54
What is band width dependent on?
mass transport
55
What is "A" in the van deemter equation
It is a constant that is offset of the Y-axis
56
What is "Cu (mu)" in the van deemter equation?
it is a linear function
57
what is mu in the van deemter equation?
The velocity of the mobile phase (aka flow rate)
58
What is "H" in the van deemter equation?
it is the plate height
59
What is the A term in the van deemter equation?
it is flow rate independent and due to different paths taken by the solute moving down the column (eddy diffusion)
60
What is Eddy Diffusion?
Different paths taken by the solute moving down the column
61
What is the B term in the van deemter equation?
It is flow rate dependent and relates to "longitudinal diffusion" along column length
62
What is the C term in the van deemter equation?
Relates to the rate of mass transfer
63
Which van deemter equation term is most complex?
The C term
64
Which van deemter equation term is called the "non-equilibrium" contribution to H?
The C term
65
What is a resolution an indicator of?
It is an indicator of separation
66
What is "df" in GCS?
the dimension of the film
67
What is the most common liquid stationary phase used in GCS?
Open tubular (WCOT)
68
What types of gas are used in GCS?
He, N2, & Ar
69
What is tR?
retention time
70
how is retention time and boiling point of an analyte related?
Retention time increases as the BP of an analyte increases
71
What exerts a strong influence on tR in GCS?
The polarity of the stationary phase
72
What is the operation principle for retention in GC based on?
Polarity, "like dissolves like"
73
What are four stationary phases used in GCS?
1. Diphenyl/dimethyl polysiloxanes
2. Cyanopropyl/phenyl/dimethyl polysiloxanes
3. Carbowax (polyethlene glycol)
4. Biscyanopropyl/cyanophenyl
74
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
1. NP
2. intermediate polarity
3. strongly polar
4. strongly polar
75
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
False
76
True or False: When a separation is entropically-driven,
| ΔG = -T∆S.
True
77
Name two of the “Big Three of Chromatography”
Retention, efficiency, & resolution
78
True or False: As the particle size (dp) increases, the efficiency of a GC separation which employs a packed column decreases.
True
79
True or False: When a separation is entropically-driven, ΔH ≠ 0.
False
80
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.
True
81
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.
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
What are the six advantages of GC?
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
What are the three limitations of GC?
1. samples must be volatile
2. samples must be temperature-stable
3. Large-scale separations are not always feasible
84
In WCOT, what is the A term equal to?
0
85
In WCOT, what is the B term equal to?
2Dm
86
In WCOT, what is the C term equal to?
[8k'df^2/(1+k')^2Ds]
87
For a WCOT, what is the van deemter equation?
H=B/u + Cu
88
What does the term D stand for in the fick equation?
diffusion coefficient
89
As temperature increases what happen to D?
D increaases
90
When two gases or liquids are separated into two compartments, what is dc/dx?
dc/dx>0
91
When two gases or liquids are in one compartment, what is dc/dx?
dc/dx=0
92
Is diffusion of gases or liquids faster and by what order of magnitude?
Diffusion of gas is fast by 4 magnitudes
93
True of false: diffusion influences plate height in GC?
True
94
A dp decreases, what occurs to A?
it decreases
95
What needs to occur to dp to decrease H?
need to minimize dp
96
As Dm decreases, what occurs to B?
it decreases
97
To decrease H what must occur to Dm?
Dm must be minimized
98
What is the magnitude of Dm in the B term in GC?
10^-1 cm^2/s
99
In the C term in GC, which term is negligible?
The second term
100
What occurs to C as df decreases?
C decreases
101
AS temperature increases in GC, what occurs to tR, Rs, and H?
tR decreases
Rs decreases
H increases
102
What occurs at every 30C increase in temperature?
it halves tR
103
In the B term, as temperature increases, what happens to Dm?
Dm increases
104
in the C term, as temperature increases, what occurs to Ds?
Ds increases
105
In the B and C term in GC, is Dm or Ds greater?
Dm>>Ds
106
How is retention time and overlapping peaks resolved in GC?
via the use of temperature programming
107
What does it mean if a compound is combustible?
carbon-containing compound
108
which GC detector requires combustible separated compounds?
FID
109
What is an excellent detector for quantitative analysis of separated compounds?
FID
110
How does FID work?
separated compounds are injected into a hydrogen-oxygen flame and combusted
111
In FID what is produced and what does it generate?
Ions are produced which generate an ion current
112
What is and ion current?
A signal
113
What does TCD stand for?
Thermal conductivity detector
114
What is a universal detector in GC?
Thermal conductivity detector
115
What must a TCD detector use?
it must use a mobile phase of high thermal conductivity
116
What is an example of a mobile phase with high thermal conductivity?
He
117
How does a TCD work?
the difference in thermal conductivity between the mobile phase and separated compounds produces a signal proportional to the concentration of the separated compound
118
What does ECD stand for?
Electron capture detector
119
What are beta particles?
electrons
120
What detector is extremely sensitive to halogenated compounds?
ECD
121
What atoms are highly electronegative?
halogens
122
What is used in ECD and what does it do?
it uses a radionuclide as a source of beta particles which shower the stream of separated compounds
123
How does ECD work?
Separated compounds containing highly electronegative atoms capture beta particles and produce a signal proportional to the compound's concentration
124
What are the seven advantages of HPLC compared to GC?
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
What occurs in a gradient elution in HPLC?
the mobile phase composition is varied systematically during the separation
126
What are considered LC methods in HPLC?
all chromatographic. methods which employ a liquid mobile phase
127
What is the critical distinction between HPLC and GC?
the mobile phase
128
What are the components of a high performance liquid chromatograph in order of flow?
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
What is the chemical nature of the solvent reservoir and degasser in HPLC?
aqueous and non-aqueous
130
What are five types of column used in HPLC?
1, reverse phase
2. normal phase
3. ion exchange
4. ion exclusion
131
what are three detectors that can be used in HPLC?
1. spectroscopic
2. refractive index
3. conductivity
132
what is longitudinal diffusion in HPLC?
molecular diffusion of solute along the length of the column
133
What is the van deemter equation in HPLC?
H=A + B/u + Cmu + Csmu + Csu
134
In HPLC, what is the Cs term in the van deemter equation?
stationary phase mass transfer
135
In HPLC, what is the Cm term in the van deemter equation?
mobile phase mass transfer of solute in flow streams between particles
136
In HPLC, what is the term Csm in the van deemter equation?
stagnant mobile phase mass transfer of solute between the flow steam and stagnant pools of mobile phase
137
What is stationary phase mass transfer in HPLC?
diffusion of solute between mobile and stationary phases
138
In mobile phase mass transfer (Cm) in HPLC, where is the solute?
the solute is in laminar flow streams between particles
139
in the Cm term, what is Dm equal to in HPLC?
~10^-4
140
What is stagnant mobile phase mass transfer (Csm) in HPLC?
diffusion of solute between moving and stagnant pools of mobile phase
141
In the term Csm, what is Dm equal to in HPLC?
~10^-4
142
What is stationary phase mass transfer (Cs) in HPLC?
diffusion of solute between mobile and stationary phases
143
In the Cs term, what is Ds equal to in HPLC?
~10^-5
144
In HPLC, what is Ds?
diffusion coefficient in the stationary phase
145
What is DI in HPLC?
the diffusion coefficient in the liquid phase (stationary phase)
146
What is Dm in HPLC?
the diffusion coefficient in the mobile phase (liquid)
147
What is referred to as "C-term driven"?
HPLC
148
What occurs to A as dp decreases in HPLC?
A decreases
149
What must occur to dp to decrease H in HPLC?
must minimize dp
150
What occurs to Dm as B decreases in HPLC?
Dm decreases
151
In HPLC, which term is very small and why?
The B term is very small in HPLC because Dm is small
152
In HPLC, what is the magnitude of Dm?
10^-4 to 10^-5
153
In HPLC, what is the magnitude of the Cs term?
10^-5 to -6
154
In HPLC, what is the magnitude of the Csm term?
10^-4 to -5
155
In HPLC, what is the magnitude of the Cm term?
10^-4 to -5
156
In HPLC, as df and dp decreases, what occurs to the C term?
The C term decreases
157
In HPLC, what occurs to the C term as Ds and Dm decreases?
The C term increases
158
in HPLC, what must occur in the C term to decrease H?
df and dp must be minimized while maximizing Ds and Dm
159
What are the three components of the reverse phase column in HPLC?
1. solid support
2. C-X chain
3. "end cap"
160
In Reverse phase HPLC, what can the solid support of the column be made of?
1. rigid (silica)
2. hard gels (polymer)
3. macro-porous
4. spherical
5. non-spherical
161
What must dp be equal to in the solid support of reverse phase HPLC?
dp must be less than or equal to 10 um
162
In reverse phase HPLC what is the end cap made up of?
trimethylsilane group [-Si(CH3)3]
163
In reverse phase HPLC, what can the C-X chain be made up of?
1. C-8 (octyl)
2. C-18 (octadecyl)
3. phenyl
4. cyano-propyl
164
What occurs to the solid support surface in reverse phase HPLC?
silanization of the solid support surface
165
In silanization of the solid support surface in reverse phase HPLC, what reaction takes place?
-Si-OH + Cl-Si(R)3 to -Si-O-Si(R)3 + HCl
166
In silanization of the solid support surface in reverse phase HPLC, what can the R term be?
H or (1, 2, 3) alkly or aryl group
167
What are the three components in reverse phase HPLC?
1. Mobile phase
2. Stationary phase
3. Solid support
168
What is the polarity of the stationary phase in reverse phase HPLC?
It is non-polar
169
What does the term k' stand for?
retention
170
In reverse phase HPLC, what is retention (k') determined by?
it is determined by non-specific hydrophobic interactions between the stationary phase and the solute
171
What does the term alpha stand for in reverse phase HPLC?
Selectivity
172
In reverse phase HPLC, what is selectivity determined by?
it is determined by the specific interactions between the mobile phase and the solute
173
What is retention time (capacity factor) determined by in reverse phase HPLC?
it is determined by the solvent strength of the mobile phase (S)
174
In reverse phase HPLC, how can the solvent strength of the mobile phase be controlled?
it can be controlled by mixing solvent of different polarity
175
What is a common non-polar solvent used in reverse phase HPLC?
tetrahydrofuran
176
what is meant by the term isocratic elution in HPLC?
when the mobile phase composition (its solvent strength) is held constant
177
What is meant by the term gradient elution in reverse phase HPLC?
when the mobile phase composition is continuously changing during separation
178
In reverse phase HPLC, what occurs as the slope of the gradient increases?
tR and Rs decreases
179
What is meant by the term separation in HPLC and GC?
the selectivity
180
What does the term Vr and Vm stand for?
```
Vr = peak elution volume of solute
Vm = elution volume of the mobile phase
```
181
what is the void volume in HPLC?
elution volume of the mobile phase (Vm)
182
What is efficiency determined by?
plate count (N) and plate height (H)
183
What does Rs stand for?
resolution
184
Retention in HPLC is often expressed in terms of what?
expressed in terms of volume and time
185
What does the term F stand for in HPLC?
the volumetric flow rate in mL/min
186
What does IEC stand for?
ion exchange chromatography
187
What are the components in an ion exchange chromatograph in order of flow?
1. solvent reservoirs (A & B)
2. pump/mixer
3. injector
4. IEC column
5. detector
6. waste reservoir
188
What can be used as a mobile phase in IEC?
aqueous and non-aqueous modified solutions
189
What can the elution in IEC be?
1. isocratic
| 2. gradient
190
What types of exchange modes does IEC function in?
both anion and cation exchange modes
191
What does the term X^(+ or -) refer to in IEC?
the charged site on the ion exchange resin
192
What forms do cation and anion exchange resins come in, in IEC?
both strong and weak forms
193
What do strong anion exchangers employ as the charged sites on the resin in IEC?
they employ quaternary amine groups as the charged site on the resin
194
What do weak anion exchangers employ as the charged sites on the resin in IEC?
They employ diethyl-amino groups as the charged sites on the resin
195
What do strong cation exchangers employ as the charged sites on the resin in IEC?
they employ sulfonic acid groups
196
What do weak cation exchangers employ as the charged sites on the resin in IEC?
they employ carboxymethyl groups
197
Describe briefly the similarities and differences between mass transport and mass transfer in a chromatographic separation
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
Explain briefly what is meant by an entropically-driven chromatographic separation. Name one example of an entropically-driven chromatographic separation
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
Explain briefly what is meant by an enthalpically-driven chromatographic separation. Name one example of an enthalpically-driven chromatographic separation
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
