Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Separation Techniques > Chromatography > Flashcards

Chromatography Flashcards

1
Q

Who initially designed chromatography, and for what purpose?

A

M. Tswett (botanist); separate pigments in plants using column made of calcium carbonate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

origin of the term ‘chromatography’

A

greek;

chroma = color
graphein = to write
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

the 2 phases in chromatography:

A

mobile phase

stationary phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the mobile phase? What does it do?

A

fluid that passes through/over the stationary phase
(liquid, gas, or supercritical fluid)

elutes out the various components in the sample (also called the ‘eluent’)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the stationary phase? What does it do?

A

column or surface - gel, solid, (or liquid distributed, bound, or immobilized on solid)

immobile (fixed) phase that interacts with compounds passing through (pushed by mobile phase)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the definition of chromatography?

A

separation based on difference in rate (speed) that components migrate through stationary phase (pushed by mobiled phase)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is ‘elution?’

A

process of separating components of mixture using appropriate solvents

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

When a sample is passed through a chromatography column, the ____ chemicals will pass through fastest, while ____ chemicals move slowly

A

unretained

retained (greater affinity for column)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

The results (output) diagram of chromatography is called a _____. Different compounds are shown as ______

A

chromatogram

different peaks

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is tR?

A

retention time (time between injection and max peak of analyte)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

The larger the tR, the greater the ______

A

affinity for the column (retention)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is u?

A

linear velocity of mobile phase (or non retained analyte)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

The linear velocities of retained analytes ‘B’ and ‘C’ would be expressed as:

A

vB

vC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does ‘L’ represent?

A

length of column

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is tM?

A

dead/void time

time needed for mobile phase to pass through

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

L divided by tM =

A

u (linear velocity of mobile phase)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is k’B?

A

retention factor
time the sample component stays in stationary phase vs time it resides in mobile phase

(indicates how much longer it is held back by stationary phase vs travelling straight through with mobile phase)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How to calculate k’B: (2)

A

ratio of amounts in 2 phases (stationary/mobile)

(tR(B) - tM)/tM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

different types of interaction between the stationary phase and compounds (4)

A

adsorption
partitioning (affinity based)
ion exchange (charge based)
sieving (size based)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

For ____ and ____ interactions, the stationary phase is immobilized on an inert base

A

ion exchange

partitioning

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

sieving interactions will have greater retention for (larger/smaller) particles

A

smaller (caught up inside sorbent )

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

types of liquid chromatography: (5)

A 
liquid solid (adsorption)
liquid liquid (partitioning)
ion exchange
size exclusion (sieving)
affinity (partitioning)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

types of gas chromatography techniques: (2)

A 
gas liquid (partitioning)
gas solid (adsorption)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

types of supercritical fluid chromatography:

A 
SF liquid (partitioning)
SF solid (adsorption)
25
Q

What theory did Martin and Synge come up with?

A

Plate theory:
consider chromatography as a series of 2 phase extractions (without reaching actual equlibrium due to continued movement through)

26
Q

What is the K distribution constant?

A

K = [A] in stationary phase / [A] in mobile phase

27
Q

A high K distribution constant means: _____

A

greater distribution into the stationary phase (more affinity); longer retention

28
Q

the greater the number of theoretical ‘plates’ in a column, the _____ the extraction

A

more efficient (better yield)

29
Q

What is ‘alpha?’

A

selectivity factor

30
Q

What is the selectivity factor?

A

measure of the separation of 2 components

ratio of the K distribution constants (or retention factors) for each

31
Q

T/F: alpha (selectivity factor) depends on column efficiency

A

False; independent of column efficiency

only consider the chemistry of compounds, eluent type, adsorbent chemistry

32
Q

What factors affect ‘alpha’ (selectivity factor)? (3)

A

chemistry of compounds
eluent type
adsorbent chemistry

33
Q

‘alpha’ (selectivity factor) must be _______, other wise ______

A

> 1

if alpha = 1, no chance to improve column efficiency to better separate

34
Q

The chromatogram peak should be a ____ shape

A

gaussian

35
Q

The number of _______ is used to assess column performance

A

theoretical plates (N)

36
Q

How is ‘N’ calculated?

A

N = 16 x (tR/W)^2
tR (retention time)
W (peak width at base)

37
Q

The height of each theoretical plate is given as:

A

H = L/N

38
Q

T/F: the theoretical plate approach does not explain peak broadening

A

true

39
Q

What is the equation used to describe chromatographic effiency in ‘rate theory?’
Who was behind it?

A 
H = A + B/u + C*u
u (linear v of mobile phase)
A: multipath coefficient
B: longitudinal diffusion coefficient
C: mass transfer coefficient

van Deemter

40
Q

what does ‘A’ (multipath coefficient’ in rate theory describe?

A

describes variation in analyte flow path (molecules flow down slightly different pathways, not travelling exactly same distance)

41
Q

what does ‘B’ (longitudinal coefficient’ in rate theory describe?

A

describes tendency of molecules to diffuse out in random directions (slightly drift in other directions rather than straight through column)

42
Q

what does ‘C’ (mass transfer coefficient’ in rate theory describe?

A

resistance to mass transfer; analyte is trying to equilibrate between stationary and mobile phase, but not instantaneous, and mobile phase keeps moving
=> molecules leaving stationary into mobile phase will lag behind slightly

43
Q

identical molecules will not elute out at the same time. This is known as ___ _____, and can be explained by ______

A

peak broadening

van deemter equation (A, B, C terms)

44
Q

As flow velocity increases (high flow), what happens to ‘A’ factor in the van deemter equation?

A

remains constant

45
Q

As flow velocity DECREASES, what happens to ‘C’ factor in the van deemter equation?

A

decreases

46
Q

The C term in van deemter equation can be further divided into (2)

A

Cs (stationary phase)

Cm (mobile phase)

47
Q

What happens to B factor in van deemter equation if flow is increased?

A

exponential decrease

48
Q

T/F: at a high flow rate, resistance to mass transfer will have a larger impact on band broadening than the longitudinal diffusion coefficient

A

True

49
Q

The van deemter equation for high flow?

The van deemter equation for low flow?

A

high flow:
H = A + B/u + C*u

low flow:
H = B/u + (Cs + Cm)*u

50
Q

Describe the van deemter graph:

A

plot u (mobile phase velocity) vs theoretical plate height (H)

J shaped curve (optimal efficiency is at lowest point)

51
Q

What is ‘resolution?’

A

denoted by ‘R’

characterize separation of 2 adjacent peaks

52
Q

How is R calculated?

A

(distance from mid-peaks)/(sum of peak widths divided by 2)

or

2 x (difference in retention time)/(sum of peak widths)

53
Q

A (higher/lower) resolution means better separated peaks

A

higher

54
Q

A greater number of theoretical plates is considered to be (more/less) efficient

A

more

55
Q

How is the plate number affected by column length?

A

increases with length

56
Q

How does the size of the column (stationary phase and internal diameter) affect efficiency?

A

smaller diameter -> more efficient (more plates)

57
Q

examples of non-ideal peaks (2)

A

tailing (stretched out slope after peak)

fronting (stretched out slope before peak)

58
Q

What are some practical problems that lead to non-ideal peaks?

A

overload
flow rate too high
slow injection…

Separation Techniques (12 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions