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2nd year sem 1: spectroscopy and advanced analysis > Lecture 3: Efficiency and quantification P1 (finished) > Flashcards

Lecture 3: Efficiency and quantification P1 (finished) Flashcards

1
Q

narrow peaks help you what?

A

separate compounds

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2
Q

Retention time is found where on the peak?

A

at the top

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3
Q

what another word for retention time?

A

hold- up time.

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4
Q

To diffuse the width of the peak you can measure form where?

A

base line or half way up the peak

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5
Q

Do nretained solute molecules travel down the column at the same rate as the carrier gas?

A

yes

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6
Q

quality of the separation is expressed mathematically by measuring what?

A

width
relative positions
peaks in the chromatogram

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7
Q

what are the fundamental parameters?

A
  1. retention factor (k),
  2. selectivity factor () ,
  3. column efficiency (N).
  4. resolution (R).
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8
Q

what is retention factor the measure of?

A

measure of how an analyte is

partitioned between stationary and mobile phase

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9
Q

whats the retention time equation?

A

k’= time analyse spends in sp/ time analyse spend sin mp

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10
Q

k ideally should be no more than what?

A

10

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11
Q

what is retention factor?

A

The retention factor is the ratio between the time a solute spends in the stationary and mobile phases.

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12
Q

Parameter influencing retention factor is?

A

Stationary phase

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13
Q

retention factor k slide

A

do it

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14
Q

in selectivity factor alpha is?

A

always more than 1

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15
Q

what is alpha defined as?

A

ratio of the two retention factors with the

larger one always being the numerator.

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16
Q

whats the Selectivity factor ( alpha) equation?

A

alpha=k’2/k’1 = t’2/t’1

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17
Q

what’s the t’2 and t’1 relationship int he Selectivity factor equation?

A

Where t’2 > t’1, so alpha > 1

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18
Q

what does k’ indicate?

A

k’ indicates where the peaks elute relative to Tm

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19
Q

what does the selectivity factor alpha show?

A

shows where the peaks elute relative to each other.

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20
Q

alpha represents what?

A

selectivity

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21
Q

whats k’1?

A

Retention factor of first peak

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22
Q

whats k’2?

A

Retention factor of second peak

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23
Q

what is selectivity a measure of?

A

Selectivity is a measure of the time or distance between two peaks.

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24
Q

what happens to the peaks if alpha = 1?

A

the two peaks have the same retention time and co-elute.

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25
Q

what is selectivity defined as?

A

Selectivity is defined as the ratio in retention factors.

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26
Q

what parameters influence retention factor?

A
  • Stationary phase
  • Mobile phase
  • Temperature
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27
Q

what does Band broadening do?

A

reduces the efficiency of the separation being carried out

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28
Q

what type of band should be appleid to the column?

A

Important to ensure that a narrow band of mixture is applied to the column

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29
Q

injection volumes should be kept to a ?

A

minimum

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30
Q

is diffusion faster in liquids or gases?

A

10^4 times slower in liquids

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31
Q

in what type of chromatography is band broadening a bigger problem?

A

GC

32
Q

what should happen at Pre and post column?

A

keep dead spaces and tube lengths to a minimum

33
Q

what is the standard measure of column efficiency?

A

is…the number of theoretical plates (N) generated by the column.

34
Q

what is N?

A

number of theoretical plates (N) generated by the column.

35
Q

whats the equation for N?

A

N= 16 tr^2 / W^2

36
Q

in simple terms what does the N equation measure?

A

peak narrowness

37
Q

what doe stem theoretical plate model suppose?

A

supposes that the chromatographic column contains a large number of separate layers, called theoretical plates.

38
Q

what happen sin these plates according to the theoretical plate model?

A

Separate equilibrations of the sample between the SP and MP occur

39
Q

How analyte moves down the column?

A

by transfer of equilibrated mobile phase from one plate to the next.

40
Q

do plates actually exist?

A

do not

really exist

41
Q

Theoretical Plate Model helps us do what?

A
  • understand the processes at work in
    the column.
  • measuring column efficiency
42
Q

N is?

A

column efficiency ( and plate number)

43
Q

Are columns with high plate numbers less or more efficient ?

A

more efficient

44
Q

A column with a high N will lead to what type of peak?

A

narrower peak at a given RT than lower N

45
Q

what parameters influence column efficiency?

A
  • Column length (increasing colum length increases efficiency)
  • Particle size (decreasing particle size increases efficiency)
46
Q

what snaother way to measure column efficiency?

A

height equivalent to a

theoretical plate

47
Q

whats H units?

A

mm

48
Q

H =?

A

L/N

49
Q

whats L in the equation?

A

length of column (mm)

50
Q

The shorter each theoretical plate, the…..

A

more plates are “contained” in any length of column.

51
Q

what does smaller plate height mean?

A

smaller plate high means narrower band width means narrower peak means better separation

52
Q

what is R?

A

resolution

53
Q

The measure of good chromatography is whether or not the peaks are what?

A

adequately separated

54
Q

what does resolution describe?

A

Resolution describes the ability of a column to separate the peaks of interest.

55
Q

what does resolution take into consideration?

A

efficiency (N), selectivity (a) and retention (k).

56
Q

whats the minimum value for measurable separation and adequate quantitation?

A

one

57
Q

A value of __is required to discern a valley between two equal-height peaks.

A

0.6

58
Q

Values of 1.7 or greater generally are desirable for what?

A

rugged methods.

59
Q

A value of what is considered a baseline separation and ensures the most accurate quantitative result?

A

1.6

60
Q

whats the R equation?

A

R=square root N/a times (a-1/a) (k’2/1+k’av)

61
Q

whats K’av?

A

k’av is the average retention factor for the two peaks.

62
Q

the valley between two peaks should do what?

A

return to the baseline.

63
Q

whats the minimum value for R?

A

1.2

64
Q

what ha stew hgihest influence eon resolution?

A

Selectivity

65
Q

Small changes in selectivity lead to big changes in ?

A

resolution

66
Q

Efficiency describes what?

A

the separation power of the column.

67
Q

Retention has a significant influence at?

A

small k-values.

68
Q

How can R be improved?

A

Increasing k’ , increasing N, changing alpha

69
Q

what the issue with increasing k’ to improve resolution?

A

the peaks become broader resulting in a loss in sensitivity.

70
Q

How does increasing N improve R?

A

improves R, but only by a square root relationship.

71
Q

whats the best way to improve R?

A

Changing  is by far the most powerful way to improve resolution

72
Q

why is alpha the best way to improve R?

A

small change can have a dramatic effect

73
Q

Resolution is a function of column efficiency of which the standard measure is what?

A

theoretical plates (N)/metre

74
Q

how is N related to the length of the column?

A

N = L/HETP

75
Q

what is HETP ?

A

the height for a single theoretical plate.

76
Q

If all other parameters remain fixed, what will a 2 fold increase in column length do?

A

will lead to a two fold increase in N.

77
Q

when a 2 fold increase in column length is done whats the negative outcome?

A

doubles the analysis time because the solute bands will take twice as long to migrate through the column.

2nd year sem 1: spectroscopy and advanced analysis (5 decks)

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