Lecture 3: Efficiency and quantification P1 (finished)

Question 1

narrow peaks help you what?

Answer 1

separate compounds

Question 2

Retention time is found where on the peak?

Answer 2

at the top

Question 3

what another word for retention time?

Answer 3

hold- up time.

Question 4

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

Answer 4

base line or half way up the peak

Question 5

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

Answer 5

yes

Question 6

quality of the separation is expressed mathematically by measuring what?

Answer 6

width
relative positions
peaks in the chromatogram

Question 7

what are the fundamental parameters?

Answer 7

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

Question 8

what is retention factor the measure of?

Answer 8

measure of how an analyte is

partitioned between stationary and mobile phase

Question 9

whats the retention time equation?

Answer 9

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

Question 10

k ideally should be no more than what?

Answer 10

10

Question 11

what is retention factor?

Answer 11

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

Question 12

Parameter influencing retention factor is?

Answer 12

Stationary phase

Question 13

retention factor k slide

Answer 13

do it

Question 14

in selectivity factor alpha is?

Answer 14

always more than 1

Question 15

what is alpha defined as?

Answer 15

ratio of the two retention factors with the

larger one always being the numerator.

Question 16

whats the Selectivity factor ( alpha) equation?

Answer 16

alpha=k’2/k’1 = t’2/t’1

Question 17

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

Answer 17

Where t’2 > t’1, so alpha > 1

Question 18

what does k’ indicate?

Answer 18

k’ indicates where the peaks elute relative to Tm

Question 19

what does the selectivity factor alpha show?

Answer 19

shows where the peaks elute relative to each other.

Question 20

alpha represents what?

Answer 20

selectivity

Question 21

whats k’1?

Answer 21

Retention factor of first peak

Question 22

whats k’2?

Answer 22

Retention factor of second peak

Question 23

what is selectivity a measure of?

Answer 23

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

Question 24

what happens to the peaks if alpha = 1?

Answer 24

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

Question 25

what is selectivity defined as?

Answer 25

Selectivity is defined as the ratio in retention factors.

Question 26

what parameters influence retention factor?

Answer 26

* Stationary phase * Mobile phase * Temperature

Question 27

what does Band broadening do?

Answer 27

reduces the efficiency of the separation being carried out

Question 28

what type of band should be appleid to the column?

Answer 28

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

Question 29

injection volumes should be kept to a ?

Answer 29

minimum

Question 30

is diffusion faster in liquids or gases?

Answer 30

10^4 times slower in liquids

Question 31

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

Answer 31

GC

Question 32

what should happen at Pre and post column?

Answer 32

keep dead spaces and tube lengths to a minimum

Question 33

what is the standard measure of column efficiency?

Answer 33

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

Question 34

what is N?

Answer 34

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

Question 35

whats the equation for N?

Answer 35

N= 16 tr^2 / W^2

Question 36

in simple terms what does the N equation measure?

Answer 36

peak narrowness

Question 37

what doe stem theoretical plate model suppose?

Answer 37

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

Question 38

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

Answer 38

Separate equilibrations of the sample between the SP and MP occur

Question 39

How analyte moves down the column?

Answer 39

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

Question 40

do plates actually exist?

Answer 40

do not | really exist

Question 41

Theoretical Plate Model helps us do what?

Answer 41

- understand the processes at work in the column. - measuring column efficiency

Question 42

N is?

Answer 42

column efficiency ( and plate number)

Question 43

Are columns with high plate numbers less or more efficient ?

Answer 43

more efficient

Question 44

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

Answer 44

narrower peak at a given RT than lower N

Question 45

what parameters influence column efficiency?

Answer 45

* Column length (increasing colum length increases efficiency) * Particle size (decreasing particle size increases efficiency)

Question 46

what snaother way to measure column efficiency?

Answer 46

height equivalent to a | theoretical plate

Question 47

whats H units?

Answer 47

mm

Question 48

H =?

Answer 48

L/N

Question 49

whats L in the equation?

Answer 49

length of column (mm)

Question 50

The shorter each theoretical plate, the.....

Answer 50

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

Question 51

what does smaller plate height mean?

Answer 51

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

Question 52

what is R?

Answer 52

resolution

Question 53

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

Answer 53

adequately separated

Question 54

what does resolution describe?

Answer 54

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

Question 55

what does resolution take into consideration?

Answer 55

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

Question 56

whats the minimum value for measurable separation and adequate quantitation?

Answer 56

one

Question 57

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

Answer 57

0.6

Question 58

Values of 1.7 or greater generally are desirable for what?

Answer 58

rugged methods.

Question 59

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

Answer 59

1.6

Question 60

whats the R equation?

Answer 60

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

Question 61

whats K'av?

Answer 61

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

Question 62

the valley between two peaks should do what?

Answer 62

return to the baseline.

Question 63

whats the minimum value for R?

Answer 63

1.2

Question 64

what ha stew hgihest influence eon resolution?

Answer 64

Selectivity

Question 65

Small changes in selectivity lead to big changes in ?

Answer 65

resolution

Question 66

Efficiency describes what?

Answer 66

the separation power of the column.

Question 67

Retention has a significant influence at?

Answer 67

small k-values.

Question 68

How can R be improved?

Answer 68

Increasing k' , increasing N, changing alpha

Question 69

what the issue with increasing k' to improve resolution?

Answer 69

the peaks become broader resulting in a loss in sensitivity.

Question 70

How does increasing N improve R?

Answer 70

improves R, but only by a square root relationship.

Question 71

whats the best way to improve R?

Answer 71

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

Question 72

why is alpha the best way to improve R?

Answer 72

small change can have a dramatic effect

Question 73

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

Answer 73

theoretical plates (N)/metre

Question 74

how is N related to the length of the column?

Answer 74

N = L/HETP

Question 75

what is HETP ?

Answer 75

the height for a single theoretical plate.

Question 76

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

Answer 76

will lead to a two fold increase in N.

Question 77

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

Answer 77

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