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Chem 211 > Unit 5 > Flashcards

Unit 5 Flashcards

(58 cards)

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1
Q

What is the state of stationary phase in column chromatography

A

Solid

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2
Q

What is the state of mobile phase in column chromatography

A

Liquid

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3
Q

What is chromatography

A

Technique used to separate compounds in mixture

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4
Q

What does partition coefficient tell (K=mobile/stationary)

A

Which state A1 or A2 the analyte prefers to be in

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5
Q

What is liquid-liquid extraction dependent on

A

Ionic strength, pH, solvent etc..

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6
Q

What is a method of measuring the progression of a reaction

A

Thin Layer Chromatography

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7
Q

Partition vs Adsorption Chromatography

A

Partition is when the solute is absorbed into the other face while Adsorbance is when it sticks to the surface of the other phase

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8
Q

Examples of Adsorption Chromatography

A

TLC or Column Chromatography

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9
Q

Examples of Partition Chromatography

A

HPLC

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10
Q

What is the stationary phase in TLC or column chromatography made of

A

silica or alumina

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11
Q

In normal HPLC what is the polarity of the column

A

Polar

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12
Q

In reversed HPLC what is the polarity of the column

A

Non-Polar

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13
Q

Effect of polarity on elution in normal HPLC

A

Non-Polar elutes first and Polar elutes last

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14
Q

Effect of polarity on elution in reversed HPLC

A

Polar elutes first and Non-Polar elutes last

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15
Q

What is dead time in HPLC

A

Time spent in mobile phase
(tm)

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16
Q

What is retention time in HPLC

A

Time for analyte to elute (tr)

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17
Q

What is retention factor

A

time in stationary/ time in mobile (t’r/tm)

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18
Q

What is t’r

A

retention time after being corrected for tm (tr-tm=t’r)

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19
Q

What is the equation for efficiency of separation with good resolution

A

R= (2|trb-tra|)/ (Δtb+Δta)

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20
Q

What is tr(x)

A

the time of elution of compound X

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21
Q

what is Δtr(x)

A

the amount of time that compound X was being eluted

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22
Q

What is (FWHM)x

A

The full width (Δtr(x)) at half of the max signal for compound X

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23
Q

Is a high or low number of plates for efficient and why

A

More plates is more efficient because it gives a narrower peak/ better resolution

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24
Q

What does N=L/H show

Study These Flashcards
A

Relationship between # of theoretical plates and length/height of column

25
What does N=(16(tr)^2)/(w)^2 show
Relationship between # of theoretical plates and time of elution and how long it took for the compound to be eluted (width of peak/resolution)
26
Why are later eluted compounds more poorly resolved, Longitudinal Diffusion
From, N=(16(tr)^2)/(w)^2, if N in constant later eluting compounds (higher tr) will result in larger w (width of peak)
27
What is Eddy Diffusion
Diffusion due to particles being different shapes and sizes, they'll take different pathways, poorer resolution
28
What is Mass Transfer
Equilibrium between the stationary and mobile phase, flow rate effects this
29
What is Longitudinal Diffusion
Diffusion due to the solute going from high to low concentration, wider peaks because later elution
30
Van Deemter Equation
H = A + B/v + Cv
31
What does A in Van Deemter Equation mean
Eddy Diffusion
32
What does B in Van Deemter Equation mean
Longitudinal Diffusion
33
What does C in Van Deemter Equation mean
Mass Transfer
34
Why does Van Deemter Equation contradict itself
B wants a high flow rate, faster elution but C wants a smaller flow rate, more time to reach equilibrium
35
What does H in Van Deemter Equation mean
Plate Height (WE WANT TO MINIMIZE)
36
What does v in Van Deemter Equation mean
flow rate
37
What are the axes on Van Deemter graph
Y= Plate Height X=Flow rate
38
What is effected before optimum flow rate
B, longitudinal diffusion
39
What is effected after optimum flow rate
C, mass transfer
40
Isocratic Elution
When the mobile phase is kept constant
41
Gradient Elution
When the mobile phase changes
42
Why is Gradient Elution beneficial
by changing the polarity of the mobile phase the elution time can be decreased thus resolution can be increased
43
Van Deemeter Equation in GC
H = B/v + Cv...No A because no packing of column
44
What predicts elution in GC?
Boiling point, lower=first
45
What is split injection for GC
Some of sample goes to waste to prevent overloading the column
46
Does GC or LC have better resolution and why?
GC because there is smaller plate height thus more theoretical plates
47
Effect of particle size on separation efficiency
Smaller=better
48
HPLC Instrumentation order
Pump, Injector, Column, Detector, Computer
49
GC Instrumentation order
Mobile Phase (gas), Flow Regulator, Injector, Column (w/oven), detector, computer
50
What does pump do in HPLC
Forces mobile phase through column
51
What does Injector do
introduces sample to columns
52
What does column do
separates compounds
53
What does detector do in chromatography
produces signal upon elution
54
In reversed phase gradient HPLC what do you want the properties of the mobile to be
Polar -> Non-Polar
55
In normal phase gradient HPLC what do you want the properties of the mobile to be
Non-Polar -> Polar
56
Benefits of superficially porous particles
Allows for shorter diffusion lengths, Improves mass transfer because the inside is solid and thus the particles are pushed closer to the outside of the column
57
What is the gradient elution equivalent for GC
temperature programming
58
What is the purpose of the Z-shaped flow cell in liquid HPLC?
Higher path length which will increase sensitivity because it will increase the slope of calibration curve

Chem 211 (5 decks)

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