Question 1

Chromatographic attractive forces forming between two molecules with formal positive and negative charges are known as:&#10;A)dispersive (van der Waals) forces&#10;B)dipolar forces&#10;C)hydrogen bonding forces&#10;D)dielectric forces

Accepted Answer

Dielectric interactions are seen in chromatographic systems where the stationary phase contains a formal charge, and the solute molecules contain the opposite formal charge.These opposite electrical charges result in strong attractive forces associated with chromatographic retention.

Question 2

Chromatographic attractive forces that result from one molecule inducing a temporary separation of charges in an adjacent molecule are known as:&#10;A)dispersive (van der Waals) forces&#10;B)dipolar forces&#10;C)hydrogen bonding forces&#10;D)dielectric forces

Accepted Answer

Dispersive interactions between molecules result when one molecule temporarily induces polarization of electrons in an adjacent molecule.The result is a temporary attraction between the two molecules.Dispersive interactions are the weakest interactions associated with chromatographic retention.

Question 3

Given the following data, calculate the resolution between the two solutes.
Peak A: peak begins at 1.40 minutes
Peak maximum occurs at 1.45 minutes
Peak returns to baseline at 1.50 minutes
Absorbance at peak maximum is 1.200
Peak B: peak begins at 1.55 minutes
Peak maximum occurs at 1.65 minutes
Peak returns to baseline at 1.75 minutes
Absorbance at peak maximum is 0.475

A)0.67
B)1.33
C)2.0
D)4.0

1.33

Accepted Answer

The equation to calculate resolution is R = d₂ - d₁½/(w₁ + w₂).Inserting the data provided:
R = 1.65 - 1.45/½(0.1 + 0.2); R = 0.2/0.15; R = 1.33

Question 4

Chromatographic attractive forces involving molecules that have a permanent dipole are known as:&#10;A)dispersive (van der Waals) forces&#10;B)dipolar forces&#10;C)hydrogen bonding forces&#10;D)dielectric forces

Accepted Answer

Dipole interactions are seen in molecules that have permanent partial positive and negative centers that cause molecules to be attracted to centers of opposite charge on adjacent molecules, resulting in strong attractive forces associated with chromatographic retention.

Question 5

The desired resolution for good quantitative or qualitative chromatographic analysis is ______ or greater.&#10;A)0.4&#10;B)0.8&#10;C)1.0&#10;D)1.25

Accepted Answer

A resolution of 1.25 or greater is required for good quantitative and qualitative chromatographic analysis.A resolution of 1.25 is where baseline separation between two peaks occurs.

Question 6

Chromatography is best characterized as a separation technique in which the components of a mixture are separated based on:&#10;A)how the components distribute between the mobile phase and stationary phase&#10;B)how well the components dissolve in the mobile phase&#10;C)the chromophoric nature of the components&#10;D)the varying concentrations of the components

Accepted Answer

Components of the mixture with higher affinity for the stationary phase will have a greater association with the stationary phase and move slower through the chromatographic system.Components with a higher affinity for the mobile phase will have a greater association with the mobile phase and move more rapidly through the chromatographic system.This differential migration will result in the separation of the components of the mixture.

Question 7

Considering the chromatographic separation of two solutes that are present in a mixture at the same concentration and produce the same detector response (i.e., have the same molar absorptivity), the solute that has a higher affinity for the stationary phase will have a ______ retention time and a ______ detector response than the solute that has a higher affinity for the mobile phase.

A)greater, greater
B)lesser, greater
C)greater, lesser
D)lesser, lesser

Accepted Answer

Solutes that have a higher affinity for the chromatographic stationary phase will be retained by the system longer, resulting in a greater retention time.As this solute stays on the column longer, the solute will be subject to band spreading.As a result of band spreading, the peak height will decrease, resulting in a broader and shorter zone that has a lesser detector response.

Question 8

Chromatographic attractive forces resulting when the small atom size approaches very close to the negative end of a dipole are known as:&#10;A)dispersive (van der Waals) forces&#10;B)dipolar forces&#10;C)hydrogen bonding forces&#10;D)dielectric forces

Accepted Answer

A special category of dipolar interactions is seen with molecules capable of forming intermolecular hydrogen bonds with an electronegative center of another molecule.The hydrogen atom has a high degree of positive character when covalently linked to an electronegative atom such as oxygen.Because of its small size, this hydrogen atom with its high degree of positive character can approach the negative end of a neighboring dipole very closely, forming a strong interactive force associated with chromatographic retention.

Question 9

The type of chromatography in which separation occurs by differential distribution of solutes between two immiscible liquids is known as:&#10;A)adsorption chromatography&#10;B)partition chromatography&#10;C)ion-exchange chromatography&#10;D)gel-permeation chromatography

Accepted Answer

Partition chromatography is based on the differential distribution of solute between two immiscible phases.

Question 10

In reversed-phase chromatography, the mobile phase is relatively ______, and the stationary phase is relatively ______.______ solute molecules are least retained in this type of chromatography.&#10;A)polar, nonpolar, polar&#10;B)polar, nonpolar, nonpolar&#10;C)nonpolar, polar, polar&#10;D)nonpolar, polar, nonpolar

Accepted Answer

In reversed-phase chromatography, the mobile phase is relatively polar, and the stationary phase is relatively nonpolar.Nonpolar solute molecules will interact more strongly with the stationary phase, whereas polar solute molecules will stay associated with the mobile phase longer.Thus the more polar solute molecules will be least retained in this type of chromatography.

Question 11

What is the correct interpretation of column selectivity (&#945;) = 1.0?&#10;A)The separation of the solutes has been optimized, and no further improvement can be made in chromatographic conditions.&#10;B)The solutes are adequately separated by the chromatographic system.&#10;C)The solutes are partially separated by the chromatographic system.&#10;D)The solutes are not separated by the chromatographic system.

Accepted Answer

The answer of What is the correct interpretation of column...

Question 12

Which of the following molecular characteristics forms the basis for chromatographic retention in adsorption and partition chromatography?&#10;A)molecular size and shape&#10;B)polarity&#10;C)molar absorptivity&#10;D)all of the above

Accepted Answer

The answer of Which of the following molecular characteristics forms...

Question 13

Suppose drug A and drug B are to be separated by anion-exchange chromatography.Drug A is an acid with a pKₐ of 8.0, and drug B is an acid with a pKₐ of 4.0.Following the proper steps to place the mixture of drugs onto the anion-exchange phase, the pH of the mobile phase should be adjusted to ______ to elute drug A only.Then the pH of the mobile phase should be adjusted to _____ to elute drug B from the stationary phase.

A)4.0, 8.0
B)8.0, 4.0
C)10.0, 6.0
D)6.0, 2.0

Accepted Answer

The answer of Suppose drug A and drug B are...

Question 14

Chromatographic methods may be characterized according to:&#10;A)the physical state of the mobile phase&#10;B)the physical apparatus associated with the stationary phase&#10;C)the mechanism of separation&#10;D)all of the above

Accepted Answer

The answer of Chromatographic methods may be characterized according to:&#10;A)the...

Question 15

Given the following data, calculate the resolution between the two solutes.
Peak A: peak begins at 1.40 minutes
Peak maximum occurs at 1.45 minutes
Peak returns to baseline at 1.50 minutes
Absorbance at peak maximum is 1.200
Peak B: peak begins at 1.55 minutes
Peak maximum occurs at 1.65 minutes
Peak returns to baseline at 1.75 minutes
Absorbance at peak maximum is 0.475

A)0.67
B)1.33
C)2.0
D)4.0

1.33

Accepted Answer

The answer of Given the following data, calculate the column...

Question 16

In normal-phase chromatography, the mobile phase is relatively ______, and the stationary phase is relatively ______._____ solute molecules are retained the longest in this type of chromatography.&#10;A)polar, nonpolar, polar&#10;B)polar, nonpolar, nonpolar&#10;C)nonpolar, polar, polar&#10;D)nonpolar, polar, nonpolar

Accepted Answer

The answer of In normal-phase chromatography, the mobile phase is...

Question 17

Given the following data, calculate the resolution between the two solutes.
Peak A: peak begins at 1.40 minutes
Peak maximum occurs at 1.45 minutes
Peak returns to baseline at 1.50 minutes
Absorbance at peak maximum is 1.200
Peak B: peak begins at 1.55 minutes
Peak maximum occurs at 1.65 minutes
Peak returns to baseline at 1.75 minutes
Absorbance at peak maximum is 0.475

A)0.67
B)1.33
C)2.0
D)4.0

Accepted Answer

The answer of Given the following data, calculate the capacity...

Question 18

Which of the following steps could be taken to improve column selectivity (&#945;)?&#10;A)Change the volume of the sample analyzed.&#10;B)Change the mobile phase flow rate.&#10;C)Change the composition of the stationary phase.&#10;D)All of the above.

Accepted Answer

The answer of Which of the following steps could be...

Question 19

Given that adsorption chromatography is being utilized with a polar adsorbent such as silica, predict the order of elution of the following three compounds with the first to elute being listed first.
Compound A - nonpolar compound with minimal potential for hydrogen bonding
Compound B - polar compound with intermediate potential for hydrogen bonding
Compound C - polar compound with high potential for hydrogen bonding

A)compound A, compound B, compound C
B)compound A, compound C, compound B
C)compound B, compound C, compound A
D)compound C, compound B, compound A

Accepted Answer

The answer of Given that adsorption chromatography is being utilized...

Question 20

The advantage of reporting column chromatography results in terms of capacity factor is that capacity factor does not vary with:&#10;A)mobile phase flow rate&#10;B)chromatography column dimensions&#10;C)sample volume injected&#10;D)any of the above

Accepted Answer

The answer of The advantage of reporting column chromatography results...

Deck 3: Chromatography and Mass Spectrometry: Theory, Practice, and Instrumentation