Chromatography is a crucial analytical method used to identify, separate, and purify mixture components for quantitative and qualitative analysis. The foundation of chromatography is the idea that, under the influence of the mobile phase, each element migrates through the stationary phase at a different rate.
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Definition: A technique used to separate a sample into its component parts is liquid chromatography. Based on how the sample interacts with the mobile and stationary phases, this separation happens. |
Liquid Chromatography Chemistry Questions with Solutions
Q-1: Define the following:
a) Stationary Phase
b) Gradient Elution
Answer:
a) Stationary Phase: It is the phase through which the mobile phase passes. In most cases, it is a solid phase or a layer of liquid that has been adsorbed onto the surface of the concrete.
b) Gradient Elution: A chromatographic separation in which the composition of the mobile phase changes during the run. It is typically found in liquid chromatography.
Q-2: What criterion is used in liquid chromatography to select the mobile phase?
Answer: The mobile phase in the liquid chromatography will be chosen based on its polarity relative to the stationary phase and the sample. A polar solvent used as the mobile phase will be adsorbed by a strong polar adsorbent stationary phase, such as alumina, which may displace sample molecules in the mixture and cause the sample components to elute very quickly.
It is best to begin elution with a solvent that is less polar to elute the components that are weakly adsorbed to the stationary phase first because this will provide less effective sample separation.
Q-3: Which of the following is not a column-type of liquid chromatography?
a) Ion Chromatography
b) Paper Chromatography
c) Affinity Chromatography
d) Liquid- Solid Chromatography
Answer: b) Paper Chromatography
Explanation: Paper chromatography is not a column method. It makes use of strips of filter paper hollow cylinders.
Q-4: What are the drawbacks of using a reciprocating pump in liquid chromatography?
Answer: The following are the disadvantages of using the reciprocating pump in liquid chromatography:
- Reciprocating pumps have high wear and tear; therefore, it necessitates extensive maintenance.
- The flow is extremely low and cannot be used for high-flow operations.
- They are larger and bulkier in shape.
- This pump has a high initial cost.
- It has a low discharge capacity.
- It is difficult to pump viscous liquids.
Q-5: What role does a guard column play in liquid chromatography?
Answer: When particles causing precipitation come into contact with the stationary or mobile phase, they are removed by the guard column. It comes before the separation column.
Q-6: Which of the following columns is not used in high performance liquid chromatography?
a) Analytical Column
b) Guard Column
c) Capillary column
d) All of the above
Answer: c) Capillary column
Explanation: Except capillary columns, all other columns are used in high performance liquid chromatography. In gas chromatography, a capillary column is used.
Q-7: List the various applications of liquid chromatography.
Answer: The various applications of liquid chromatography are:
- Ink samples are tested using liquid chromatography.
- It’s used in environmental testing and cleanliness checks.
- It’s used in food testing and quality control.
- It is employed in the pharmaceutical and chemical industries.
- It is employed in forensic science as well as in hospitals.
Q-8: Which of the following statements is correct for normal phase HPLC?
a) The stationary phase is nonpolar, and the mobile phase is polar.
b) The mobile phase is nonpolar, while the stationary phase is polar.
c) Adding a more polar solvent to the mobile phase increases eluent strength.
d) Adding a less polar solvent to the mobile phase increases eluent strength.
Answer:b) The mobile phase is nonpolar, while the stationary phase is polar.
Q-9: Which of the following compounds would you expect to be the last to elute from a reverse phase liquid chromatography column?
a) CH3OH
b) CH3CH2OH
c) CH3CH2CH2OH
d) CH3CH2CH2CH2OH
Answer: d) CH3CH2CH2CH2OH
Explanation: Compounds with low boiling points elute first, followed by compounds with higher boiling points. The boiling point rises with increasing molecular weight. As a result of its large molecular weight and long carbon chain, CH3CH2CH2CH2OH (Butanol) has the highest boiling point. Therefore, it will elute last from a reverse phase liquid chromatography column.
Q-10: What is the most common way to increase the retention of analytes in HPLC?
Answer: In HPLC, use lower flow rates and mobile phases with different polarities than the mobile phase to increase the retention of analytes in HPLC.
Q-11: Give an example of a mobile phase that could be used for reverse phase HPLC separation.
Answer: Water/methanol and water/acrylonitrile are some examples that can be used as a mobile phase in reverse phase HPLC separation.
Q-12: What are the advantages of reducing the internal diameter of the column?
Answer: Reducing the internal diameter of the column helps in increasing resolution.
Q-13: Give an example of a stationary phase that might be used for reverse phase HPLC separation.
Answer: C18 (ODS), C8, C4, and phenyl are all acceptable for reverse phase HPLC separation.
Q-14: Which of the following is the proper abbreviation for HPLC?
a) High Performance Liquid Chromatography
b) Higher Position Liquid Chromatography
c) High Partition Liquid Chromatography
d) Higher Property Liquid Chromatography
Answer: a) High Performance Liquid Chromatography
Q-15: Theoretical plates are employed in the __________.
a) Determination of the thickness of the stationary phase
b) Estimation of the column efficiency
c) Measurement of analyte distribution between mobile and stationary phases
d) All of the above
Answer: b) Estimation of the column efficiency
Practice Questions on Liquid Chromatography
Q-1: What kind of physical state does the mobile phase in liquid chromatography exist in?
a) Solid
b) Liquid
c) Gas
d) Plasma
Q-2: Identify the kind of liquid chromatography that employs immobilised biochemicals as a stationary phase.
a) Exclusion Chromatography
b) Affinity Chromatography
c) Gel Permeation Chromatography
d) Ion Exchange Chromatography
Q-3: What does chiral chromatography mean?
Q-4: How can we improve the separation efficiency of liquid chromatography?
Q-5: What are the functions of pulse dampers or flow smootheners in liquid chromatography?
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