Chapter 2 - Basic terms and concepts

Question 1

The term “sample component” is used interchangeably with

Answer 1

“analyte” and “solute”.

Question 2

The most common stationary phase in RPC is

Answer 2

hydrophobic C18-bonded phase on a porous silica support.

Question 3

The term “sorbent” refers to

Answer 3

the bonded phase.

Question 4

The term “support” refers to the

Answer 4

unbonded silica material.

Question 5

Retention time (t_R)

Answer 5

The time between the sample injection and the peak maximum.

Question 6

Void time (t_M).

Answer 6

The total time spent by any unretained component in the mobile phase within the column.

Question 7

The adjusted retention time (t_R^’) is equal to

Answer 7

the time the solute resides in the stationary phase (t_R - t_M).

Question 8

w_b

Answer 8

Peak width measured at the base.

Question 9

w_½

Answer 9

Peak width measured at the peak’s half-height.

Question 10

For Gaussian peaks, w_b is approximately equal to

Answer 10

four times the standard deviation.

Question 11

The height or area of a peak is proportional to

Answer 11

the amount of analyte component present in the sample.

Question 12

Peak area is more commonly used to perform

Answer 12

quantitative calculations.

Question 13

The retention volume (V_R) is

Answer 13

the volume of mobile phase needed to elute the analyte at a given flow rate (F).

Question 14

Retention volume equation

Answer 14

V_R = t_RF

Question 15

Void volume equation

Answer 15

V_M = t_MF

Question 16

The void volume is the

Answer 16

total volume of the mobile phase contained in the column.

Question 17

For most columns, the void volume can be estimated by

Answer 17

V_M = 0.65V_c = 0.65(pi)r²L

Question 18

Peak volume equation

Answer 18

Peak volume = w_bF

Question 19

Retention factor (k) is

Answer 19

the degree of retention of the analyte in the column.

Question 20

Retention factor is defined as

Answer 20

the time the solute resides in the stationary phase (t_R^’) relative to the time it resides in the mobile phase (t_M).

Question 21

Retention factor equation

Answer 21

k = t_R^’/t_M

Question 22

Retention volume equation

Answer 22

V_R = V_M(1 + k)

Question 23

A peak with k = 0 means that

Answer 23

a component is not retained by the stationary phase and elutes with the solvent front.

Question 24

A value of k > 20 indicates that

Answer 24

the component is highly retained.

Question 25

The desired k values for most analyses are between

Answer 25

1 and 20.

Question 26

Separation factor or selectivity (alpha) is

Answer 26

a measure of the relative retention (k₂/k₁) of two sample components.

Question 27

Selectivity must be ______ for physical peak separation to occur.

Answer 27

\> 1.0

Question 28

Selectivity is a measure of

Answer 28

differential migration.

Question 29

Changing alpha is the most effective way to

Answer 29

separate two closely eluting solutes.

Question 30

The number of theoretical plates or plate number (N) is a measure of

Answer 30

the efficiency of the column.

Question 31

N is defined as

Answer 31

the square of the ratio of the retention time divided by the standard deviation of the peak.

Question 32

Number of theoretical plates equation

Answer 32

N = 16(t_R/w_b)²

Question 33

For a Gaussian peak, w_½ is equal to

Answer 33

2.355 sigma

Question 34

N can only be measured under _______ conditions.

Answer 34

isocratic

Question 35

Peak volume is the

Answer 35

volume of the mobile phase, or eluent, containing the eluting peak.

Question 36

Peak volume is proportional to

Answer 36

k and V_M.

Question 37

The height equivalent to a theoretical plate (HETP or H) is equal to

Answer 37

the length of the column (L) divided by the plate number (N)

Question 38

In HPLC, the main factor controlling H is the

Answer 38

diameter of the particles (d_p) used as the packing material.

Question 39

For a well-packed column, H is roughly equal to

Answer 39

2d_p

Question 40

Resolution (R_s) definition

Answer 40

The degree of separation of two adjacent peaks.

Question 41

R_s is defined as

Answer 41

the difference in retention times of the two peaks divided by the average peak width.

Question 42

Resolution equation

Answer 42

delta (t_R)/w_b

Question 43

R_s = 0 indicates

Answer 43

complete co-elution or no separation.

Question 44

R_s = 0.6 indicates

Answer 44

that a shoulder is discernible or slight separation has been achieved.

Question 45

R_s = 1 indicates

Answer 45

partial separation, allowing for a rough quantitation.

Question 46

R_s = 1.5 indicates

Answer 46

that a baseline separation of the two components has been achieved.

Question 47

The goal of most HPLC methods is to achieve separation of

Answer 47

R_s = 1.5 for all key analytes

Question 48

The asymmetric factor (A_s) is used to

Answer 48

measure the degree of peak symmetry.

Question 49

Asymmetry factor equation

Answer 49

A_s = B/A

Question 50

Tailing factor (T_f) equation

Answer 50

T_f = W_0.05/2f

Question 51

T_f = 1.0 indicates

Answer 51

a perfectly symmetrical peak.

Question 52

T_f \> 2 indicates

Answer 52

a tailing peak that is less acceptable due to difficulty in integrating the peak area precisely.

Question 53

With a T_f between 0.5 and 2.0, the values of A_s and T_f are

Answer 53

similar.

Question 54

Peak tailing is typically caused by

Answer 54

adsorption, strong interaction with the stationary phase, or extra-column band broadening of the solute.