This set of Bioprocess Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Chromatography”.
1. Which type of mechanism is applicable to chromatography?
a) Absorption and Desorption
b) Adsorption and Absorption
c) Adsorption and Desorption
d) Adsorption and Diffusion
Explanation: Adsorption means the attraction to a substance (as opposed to absorption, which means the complete envelopment of something). Desorption is the opposite – when something is not attracted to the substance. How it relates to chromatography is through the mobile and stationary phase. Depending on what the substance adsorbs or desorbs to, will determine how it will move in the chromatogram. For example, if it adsorbs to the mobile phase, it will move a lot. However, if it adsorbs to the stationary phase, it will not move very much. This is how mixtures are separated through chromatography, as different substances in the mixture will adsorb and desorb differently, and hence will move differently, and thus separation is achieved.
2. Which of the following condition is of reverse phase chromatography?
a) The mobile phase is non-polar and stationary phase is polar
b) The mobile phase is polar and stationary phase is non-polar
c) Both the mobile phase and stationary phase are organic
d) Both the mobile phase and stationary phase are inorganic
Explanation: In reversed phase chromatography, the mobile phase is polar (like water), and the stationary phase is non-polar while in normal phase chromatography, the mobile phase is non-polar (100% organic), and the stationary phase is polar.
3. Which of type of chromatography depends on the principle of size of particles?
a) Affinity chromatography
b) Gel- filtration chromatography
c) Ion- exchange chromatography
d) Multimodal chromatography
Explanation: Gel filtration chromatography, a type of size exclusion chromatography, can be used to either fractionate molecules and complexes in a sample into fractions with a particular size range, to remove all molecules larger than a particular size from the sample, or a combination of both operations.
4. According to the small size of the particle, which type of chromatographic separation is applicable?
a) High- performance liquid chromatography (HPLC)
b) Fast protein liquid chromatography (FPLC)
c) Gel chromatography
d) Paper chromatography
Explanation: In order to achieve the high resolutions characteristic of HPLC, stationary-phase particles 2-5 μm in diameter are commonly used. Because the particles are so small, HPLC systems are operated under high pressure (5-10 MPa) to achieve flow rates of 1-5 ml min -1. FPLC instruments are not able to develop such high pressures (1-2 MPa), and are therefore operated with column packings of larger size.
5. The visual output of chromatography is called?
Explanation: The machine used is called a gas or liquid chromatograph, the data generated is called a chromatogram. It is an electronic file or hardcopy containing the information generated during the chromatography run.
6. From the graph given which component has the higher elution rate?
c) A & B
d) None of the mentioned
Explanation: Because Component A is adsorbed more strongly than B, and B is desorbed easily and has higher rate of elution as has the greater affinity towards the Stationary phase, As the solutes move through the stationary phase they separate.
7. In which of the following type of chromatography the capillary action mechanism is present?
a) Liquid chromatography
b) Gas chromatography
c) Thin- Layer chromatography
d) Paper chromatography
Explanation: The most common type of chromatography. The paper is the stationary phase. This uses capillary action to pull the solutes up through the paper and separate the solutes.
8. What does the retention factor, k’, describe?
a) The velocity from the stationary phase
b) The velocity of the mobile phase
c) The distribution of an analyte between the stationary and the mobile phase
d) The migration rate of an analyte through a column
Explanation: k’ (Capacity factor) in the chromatography is to provide a calculation or formula which defines how much interaction the solute has with the stationary phase material. And it is based on the formula given below:
Where, T (R) = Retention time of the peak in minutes
T (0) = Retention time of an unretained peak
k’ value should be >1.
9. T (0) found to be 2.60 minutes and the sample elutes at 5.70 minutes. Calculate the value of k’ and find the correct answer.
10. Theoretical plates are used to ___________
a) Determine the thickness of the mobile phase
b) Determine the thickness of the stationary phase
c) Estimate the efficiency of the column
d) Measure the distribution of the analyte between mobile and stationary phases
Explanation: The plate model supposes that the chromatographic column is contains a large number of separate layers, called theoretical plates. Separate equilibrations of the sample between the stationary and mobile phase occur in these “plates”.
11. What useful information can be found from a Van Deemter plot?
a) Optimum column length
b) Optimum column temperature
c) Optimum mobile phase flow rate
d) The selectivity factor
Explanation: The Van Deemter equation is an empirical formula describing the relationship between plate height (H, the length needed for one theoretical plate) which is a measure of column efficiency, and linear velocity (µ) . Smaller plate height values corresponds to greater peak efficiencies, as more plates, or analyte partitioning, can occur over a fixed length of column. The Van Deemter equation is governed by three cumulative terms: (A) eddy diffusion, (B) longitudinal diffusion, and (C) mass transfer. A loss in peak efficiency can be observed as a wider analyte band, and therefore, these three terms can also be viewed as factors that contribute to band broadening.
12. The paper is non-polar in paper chromatography.
Explanation: Polar components will be attracted to the water molecules attached to the cellulose (paper) and not attracted to a nonpolar solvent. The chromatogram will not contain the polar components, given that it doesn’t climb up the paper with the nonpolar solvent.
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