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Y1 - FAC1 > Chromatography I > Flashcards

Chromatography I Flashcards

1
Q

What is chromatography?

A

Analytes distribute themselves between 2 phases

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2
Q

Define stationary phase

A

Layer on supporting medium that interacts with analyte

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3
Q

Define mobile phase

A

Solvent/gas that flows through supporting medium

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4
Q

What is a super-critical fluid?

A

S/L/G coexists together

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5
Q

What is a supporting medium?

A

Solid surface where SP is bound to

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6
Q

Purpose of using chromatography

A

Check identity, purity, impurities

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7
Q

2 types of analytical methods

A

Spectroscopy, Chromatography

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8
Q

Briefly describe how spectroscopy works

A

Energy fired at sample, enters detector, signal processed

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9
Q

Difference between HPLC and GC

A

HPLC uses liquid MP

GC uses gas MP

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10
Q

Briefly describe method of chromatography

A

MP contains sample, moves through SP

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11
Q

Difference between how sample moves in TLC and HPLC

A

TLC - Capillary action

HPLC - Pump moves MP

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12
Q

What is the retention factor?

A

How sample distributes itself between MP/SP

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13
Q

If the sample is in SP for too long…

A

RF is high so retention time is high

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14
Q

Factors affecting retention

A

Composition of MP/SP
Length of column
Temperature

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15
Q

Equation Kc = Cs/Cm

What does Cs and Cm stand for?

A 
Cs = Conc of sample in SP
Cm = Conc of sample in MP
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16
Q

Describe a chromatogram

A

Detector response to compounds eluted from column (recorded as function of time)

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17
Q

How do you ensure separation?

A

Detector response needs to reach baseline between chromatographic peaks

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18
Q

Describe a graph with good separation of compounds

A

Peaks are at the same RT but narrower and the detector reaches baseline before second peak is recorded

19
Q

What is separation determined by?

A

Differences in RT
Resolution (how narrow/broad peaks are)
Selectivity (differing RT)

20
Q

The equation for retention factor, k = Kc x Vs/Vm

What does Vs and Vm stand for?

A 
Vs = Volume of SP
Vm = Void volume
21
Q

Another equation for retention factor, k = tR - tM / tM

What does tR and tM stand for?

A 
tr = Retention time of sample
tM = Hold up/dead vol time (time MP takes from injector to detector)
22
Q

Equation: Vr = Vm + KcVs

What does KcVs stand for?

A

KcVs = Additional volume needed to elute compound

23
Q

Equation Vr = tR x F

What does F stand for?

A

F = Volumetric flow rate of MP through column

24
Q

What does the peak width express?

A

How efficiently a compound transports through column

25
Q

Describe peak widths in relation to retention times

A

Narrower the peaks, more effective the column

26
Q

Describe the chromatographic plate theory

A

An equilbrium between SP/MP analytes

27
Q

When do analytes move through column?

A

When MP, so rate which analyte moves through column = Proportional to time spent in MP

28
Q

What is a column?

A

A system with number of plates, each plate represents single partition process

29
Q

Describe relations between separation and theoretical plates

A

Efficiency of chromatographic separation inc as number of t/plates inc and height of t.plate dec

30
Q

Equation N = L/H

What does each stand for?

A

N = Number of theoretical plates per column
L = Length of column in mm
H - Length of column corresponding to t.plate

31
Q

Equation a = k2/k1

What does each stand for?

A 
a = Separation factor
k2 = Retention factor of later of 2 eluting peaks
k1 = RF of first eluting peak
32
Q

Describe ‘a’

A

a = Always 1

Larger value means better selectivity

33
Q

Equation As = w0.05/2d

What does each stand for?

A 
As = Symmetry factor
w0.05 = Peak width a 1/20th of peak height
d = Distance btw perpendicular dropping from peak max/leading edge of peak at 1/20th of peak height
34
Q

Describe effect of As

A

As value of 1 = Symmetry

35
Q

What is peak tailing and peak fronting?

A

Peak tailing = ‘As’ more than 1

Peak fronting = ‘As’ less than 1

36
Q

Define resolution

A

Degree of separation between 2 peaks (Rs)

37
Q

Describe effect of Rs

A

Rs = 1 means peak separation of 94%

38
Q

When does baseline separation occur

A

When Rs value more than 1.5

39
Q

Describe deficiencies of plate theory

A

Assumes rapid equilibrium between MP/SP
Peak broadening ignored
Effect of MP ignored

40
Q

What are the 3 causes of peak broadening?

A

Eddy diffusion
Mobile phase mass transfer
Longitudinal broadening

41
Q

Describe eddy diffusion

A

Causes peak/band broadening cos of multiple flow paths through full column

42
Q

Describe mobile phase mass transfer

A

Broadened peak to equilibriate too slow to from before MP moved down column, takes analyte along

43
Q

Describe longitudinal broadening

A

Narrow at intro point of column, broadened analyte zone after intro on column

Y1 - FAC1 (3 decks)

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