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Chem 211 > Unit 5 > Flashcards

Unit 5 Flashcards

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

A

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

25
Q

What does N=(16(tr)^2)/(w)^2 show

A

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
Q

Why are later eluted compounds more poorly resolved, Longitudinal Diffusion

A

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
Q

What is Eddy Diffusion

A

Diffusion due to particles being different shapes and sizes, they’ll take different pathways, poorer resolution

28
Q

What is Mass Transfer

A

Equilibrium between the stationary and mobile phase, flow rate effects this

29
Q

What is Longitudinal Diffusion

A

Diffusion due to the solute going from high to low concentration, wider peaks because later elution

30
Q

Van Deemter Equation

A

H = A + B/v + Cv

31
Q

What does A in Van Deemter Equation mean

A

Eddy Diffusion

32
Q

What does B in Van Deemter Equation mean

A

Longitudinal Diffusion

33
Q

What does C in Van Deemter Equation mean

A

Mass Transfer

34
Q

Why does Van Deemter Equation contradict itself

A

B wants a high flow rate, faster elution but C wants a smaller flow rate, more time to reach equilibrium

35
Q

What does H in Van Deemter Equation mean

A

Plate Height (WE WANT TO MINIMIZE)

36
Q

What does v in Van Deemter Equation mean

A

flow rate

37
Q

What are the axes on Van Deemter graph

A

Y= Plate Height X=Flow rate

38
Q

What is effected before optimum flow rate

A

B, longitudinal diffusion

39
Q

What is effected after optimum flow rate

A

C, mass transfer

40
Q

Isocratic Elution

A

When the mobile phase is kept constant

41
Q

Gradient Elution

A

When the mobile phase changes

42
Q

Why is Gradient Elution beneficial

A

by changing the polarity of the mobile phase the elution time can be decreased thus resolution can be increased

43
Q

Van Deemeter Equation in GC

A

H = B/v + Cv…No A because no packing of column

44
Q

What predicts elution in GC?

A

Boiling point, lower=first

45
Q

What is split injection for GC

A

Some of sample goes to waste to prevent overloading the column

46
Q

Does GC or LC have better resolution and why?

A

GC because there is smaller plate height thus more theoretical plates

47
Q

Effect of particle size on separation efficiency

A

Smaller=better

48
Q

HPLC Instrumentation order

A

Pump, Injector, Column, Detector, Computer

49
Q

GC Instrumentation order

A

Mobile Phase (gas), Flow Regulator, Injector, Column (w/oven), detector, computer

50
Q

What does pump do in HPLC

A

Forces mobile phase through column

51
Q

What does Injector do

A

introduces sample to columns

52
Q

What does column do

A

separates compounds

53
Q

What does detector do in chromatography

A

produces signal upon elution

54
Q

In reversed phase gradient HPLC what do you want the properties of the mobile to be

A

Polar -> Non-Polar

55
Q

In normal phase gradient HPLC what do you want the properties of the mobile to be

A

Non-Polar -> Polar

56
Q

Benefits of superficially porous particles

A

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
Q

What is the gradient elution equivalent for GC

A

temperature programming

58
Q

What is the purpose of the Z-shaped flow cell in liquid HPLC?

A

Higher path length which will increase sensitivity because it will increase the slope of calibration curve

Chem 211 (5 decks)

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