Chromatography Methods Quiz Questions
Questions and Answers
- 1.
List the types of substances to which each of the following chromatographic methods is most applicable: Gas- Liquid
Explanation
Gas-liquid chromatography is most applicable to species that are somewhat volatile and thermally stable. This is because in gas-liquid chromatography, the sample is vaporized and carried by an inert gas through a liquid stationary phase. The separation of the components in the sample is based on their affinity for the stationary phase and their volatility. Therefore, species that are somewhat volatile and thermally stable are ideal for gas-liquid chromatography as they can be easily vaporized and do not decompose at the temperatures used in the process.Rate this question:
- 2.
List the types of substances to which each of the following chromatographic methods is most applicable: Liquid- adsorption
Explanation
The liquid-adsorption chromatographic method is most applicable to nonpolar low to moderate molecular mass organics, especially isomeric organic species. This is because the method involves the separation of compounds based on their affinity for the stationary phase, which in this case is a liquid. Nonpolar compounds with similar molecular masses and structures tend to have similar affinities for the stationary phase, making it easier to separate them using this method. Isomeric organic species, which have the same molecular formula but different arrangements of atoms, can also be effectively separated using liquid-adsorption chromatography.Rate this question:
- 3.
List the types of substances to which each of the following chromatographic methods is most applicable: Gas- solid
Explanation
Gas-solid chromatography is most applicable to separate low molecular mass nonpolar gases. This is because in gas-solid chromatography, the stationary phase is a solid material, which interacts with the nonpolar molecules of the sample. The nonpolar gases will have stronger interactions with the stationary phase, leading to better separation and retention times. On the other hand, polar or high molecular mass gases may not interact as strongly with the stationary phase, resulting in poor separation and retention times.Rate this question:
- 4.
List the types of substances to which each of the following chromatographic methods is most applicable: Ion exchange
Explanation
Ion exchange chromatography is most applicable to substances that are ionic or that can be derivatized to form ions. This is because ion exchange chromatography relies on the exchange of ions between the sample and the stationary phase. The stationary phase contains charged groups that attract and retain ions of opposite charge, allowing for the separation of different ionic species. Therefore, substances that are ionic or can be converted into ions are best suited for this chromatographic method.Rate this question:
- 5.
The weak mobile phase is a non-polar solvent (hexane, benzene) and the strong mobile phase is a polar solvent (water, methanol) is for polar supports
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
This statement is true because polar supports have a stronger affinity for polar solvents. In chromatography, the mobile phase is the solvent that carries the sample through the stationary phase. The stationary phase can be polar or non-polar, and the mobile phase is chosen based on its compatibility with the stationary phase. In the case of polar supports, a weak mobile phase consisting of a non-polar solvent like hexane or benzene is used, while a strong mobile phase consisting of a polar solvent like water or methanol is used for non-polar supports. This ensures that the mobile phase interacts appropriately with the stationary phase, allowing for effective separation of compounds.Rate this question:
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- 6.
The weak mobile phase is a polar solvent and the strong mobile phase is a non-polar solvent for non-polar supports.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
This statement is true because in chromatography, the mobile phase refers to the solvent that carries the sample through the stationary phase. In order to separate non-polar compounds, a polar mobile phase is used, while a non-polar mobile phase is used to separate polar compounds. This is because like dissolves like, meaning polar solvents will interact more strongly with polar compounds and non-polar solvents will interact more strongly with non-polar compounds. Therefore, a weak mobile phase that is polar and a strong mobile phase that is non-polar would be suitable for separating non-polar compounds.Rate this question:
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- 7.
Isocratic elution
Correct Answer
use of a constant mobile phase composition to elute solutesExplanation
Isocratic elution refers to the technique of using a constant mobile phase composition to elute solutes in chromatography. In this method, the mobile phase composition remains unchanged throughout the separation process, allowing all solutes to be eluted at the same rate. This is in contrast to gradient elution, where the mobile phase composition is varied over time to achieve better separation of solutes. Isocratic elution is often used when the solutes have similar retention times and do not require a gradient to be effectively separated.Rate this question:
- 8.
Changing the composition of the mobile phase with time aka solvent programming:
Correct Answer
gradient elutionExplanation
Gradient elution refers to a technique in liquid chromatography where the composition of the mobile phase is changed over time. This is also known as solvent programming. In gradient elution, a solvent gradient is created by increasing or decreasing the concentration of one or more components in the mobile phase. This allows for the separation of compounds with different polarities or affinities for the stationary phase. By gradually changing the composition of the mobile phase, gradient elution improves the resolution and efficiency of the chromatographic separation.Rate this question:
- 9.
Describe three general methods for improving resolution in partition chromatography.
- A.
Adjustment of kA and kB by employing a multicomponent mobile phase and varying the raiot of the solvents to find an optimal mixture.
- B.
Variation in the chemical composition of the solvent system in such a way as to make α larger.
- C.
Employing a different packing in which α is greater.
- D.
Going from a weak mobile phase to a strong one
Correct Answer(s)
A. Adjustment of kA and kB by employing a multicomponent mobile phase and varying the raiot of the solvents to find an optimal mixture.
B. Variation in the chemical composition of the solvent system in such a way as to make α larger.
C. Employing a different packing in which α is greater.Explanation
The three general methods for improving resolution in partition chromatography are adjusting the kA and kB by employing a multicomponent mobile phase and varying the ratio of the solvents to find an optimal mixture, varying the chemical composition of the solvent system to make α larger, and employing a different packing in which α is greater. These methods aim to enhance the separation of components in the chromatographic system, either by manipulating the mobile phase or the stationary phase to achieve better resolution.Rate this question:
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- 10.
In a stop-flow injection
Correct Answer(s)
the flow of solvent is stopped, a fitting at the head of the column is removed, and the sample is injected directly onto the head of the column. The fitting is then replaced and pumping is resumed. - 11.
A reversed-phase packing
Correct Answer(s)
is a nonpolar packing that is used in partition chromatography with a relatively polar mobile phase.Explanation
A reversed-phase packing refers to a type of packing material used in partition chromatography. It is characterized by being nonpolar, meaning it does not have a charge or affinity for polar molecules. This type of packing is used in conjunction with a relatively polar mobile phase, which is the liquid or gas that carries the sample through the column. The nonpolar packing material and polar mobile phase create a reversed-phase system, allowing for the separation and analysis of polar compounds.Rate this question:
- 12.
In a normal-phase packing,
Correct Answer(s)
the stationary phase is polar and the mobile phase is relatively nonpolar.Explanation
In a normal-phase packing, the stationary phase is polar and the mobile phase is relatively nonpolar. This means that the stationary phase has a higher affinity for polar compounds, causing them to interact and be retained longer, while nonpolar compounds will move more easily through the column with the mobile phase. This separation technique is commonly used for compounds that are more polar in nature, allowing for effective separation based on their polarities.Rate this question:
- 13.
) In ion-pair chromatography
Correct Answer(s)
a large organic counter-ion is added to the mobile phase as an ion-pairing reagent. Separation is achieved either through partitioning of the neutral ion-pair or as a result of electrostatic interactions between the ions in solution and charges on the stationary phase resulting from adsorption of the organic counter-ion.Explanation
In ion-pair chromatography, the addition of a large organic counter-ion to the mobile phase serves as an ion-pairing reagent. This reagent helps in the separation process by either partitioning the neutral ion-pair or by facilitating electrostatic interactions between the ions in solution and the charges on the stationary phase. This interaction occurs due to the adsorption of the organic counter-ion.Rate this question:
- 14.
In ion chromatography,
Correct Answer(s)
the stationary phase is an ion-exchange resin, and detection is ordinarily accomplished by a conductivity detector.Explanation
Ion chromatography is a technique used to separate and analyze ions in a sample. In this technique, the stationary phase refers to the material that retains the ions and allows for their separation. In ion chromatography, the stationary phase is an ion-exchange resin, which selectively binds and releases ions based on their charge. The detection of ions is typically done using a conductivity detector, which measures the electrical conductivity of the eluent as ions pass through it. This allows for the identification and quantification of different ions present in the sample.Rate this question:
- 15.
A bulk property detector
Correct Answer(s)
responds to some property of the mobile phase (such as thermal or electrical conductivity) that is altered by the presence of analytes.Explanation
A bulk property detector is a type of detector that is able to detect analytes based on changes in a specific property of the mobile phase, such as thermal or electrical conductivity. When analytes are present, they can alter the conductivity or thermal properties of the mobile phase, which can be measured by the detector. This allows the detector to identify the presence of analytes in a sample.Rate this question:
- 16.
A solute property detector
Correct Answer(s)
responds to some property of analytes, such as absorption or fluorescence.Explanation
The correct answer explains that a solute property detector responds to a property of analytes, such as absorption or fluorescence. This means that the detector is able to detect and measure the presence or concentration of analytes by measuring their absorption or fluorescence properties. This explanation highlights the main function and purpose of a solute property detector in analyzing and identifying analytes in a solution.Rate this question:
- 17.
What ways are normal- phase partition chromatography and adsorption chromatography similar?
Correct Answer(s)
The stationary phases in both are polar, whereas the mobile phases are relatively nonpolarExplanation
Both normal-phase partition chromatography and adsorption chromatography have polar stationary phases and relatively nonpolar mobile phases. This similarity in the polarity of the stationary and mobile phases allows for the separation of compounds based on their polarity. In both techniques, polar compounds have stronger interactions with the polar stationary phase, causing them to be retained longer and elute later, while nonpolar compounds have weaker interactions and elute earlier. This similarity in the phase polarity is essential for the effective separation of compounds in both normal-phase partition chromatography and adsorption chromatography.Rate this question:
- 18.
What types of species can be separated by HPLC but not GC?
Correct Answer(s)
Nonvolatile and thermally unstable compounds can be separated by HPLC by not GCExplanation
High Performance Liquid Chromatography (HPLC) is a technique used to separate and analyze nonvolatile compounds that cannot be vaporized without decomposition. It is also effective in separating thermally unstable compounds that may decompose at high temperatures required for Gas Chromatography (GC). In contrast, GC is suitable for separating volatile compounds that can be vaporized without decomposition. Therefore, nonvolatile and thermally unstable compounds can be separated by HPLC but not GC.Rate this question:
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