This set of Food Processing Unit Operations Multiple Choice Questions & Answers (MCQs) focuses on “Absorption Mechanisms”.
1. What is the principle behind paper chromatography?
a) It is based on partition chromatography
b) It is based on ions and its charge
c) It is based on charges only
d) It is based on ions only
View Answer
Explanation: The principle involved in paper chromatography is partition chromatography where the substances are partitioned between liquid phases. One phase is the mobile phase water which moves over the paper and other is the water which is held in the pores of the filter paper used.
2. What is Rf value?
a) Ratio of the distance moved by the solvent and the distance moved by the solute
b) Ratio of the distance moved by the solute and the distance moved by the solvent
c) Ratio of the concentration of solute and the concentration of the solvent
d) It Ratio of the concentration of solvent and the concentration of the solute
View Answer
Explanation: The Rf value is defined as the ratio of the distance moved by the solute and the distance moved by the solvent along the paper, where both distances are measured from the common application Baseline.
3. What is the best solvent for paper chromatography?
a) Water
b) Alcohol
c) Vinegar
d) Methanol
View Answer
Explanation: Paper chromatography is an inexpensive method for analyzing some types of chemical mixtures. Water is polar in nature and is commonly used as solvent in paper chromatography.
4. What does a high RF value mean in paper chromatography?
a) Substance is very non-polar
b) Substance is medium non-polar
c) Substance is polar
d) Substance is neutral
View Answer
Explanation: A high Rf would refer to a substance that is very non-polar where substance moved. A low Rf value would refer to a substance that is very polar.
5. What are the two main types of chromatography?
a) Liquid chromatography and paper chromatography
b) Liquid chromatography and gas chromatography
c) Liquid chromatography and solid chromatography
d) Solid chromatography and gas chromatography
View Answer
Explanation: Chromatography utilizes phase equilibrium partitioning principles to isolate proteins, nucleic acids in complex blends and has stationary phase and a mobile phase. There are two main types of chromatography: Liquid chromatography and gas chromatography.
6. Why acetonitrile is used as solvent in HPLC?
a) Improve chromatographic peak shape
b) Provide a source of protons in reverse phase LC/MS
c) Provide a source of electrons in reverse phase LC/MS
d) Improve chromatographic peak shape and provide a source of protons in reverse phase LC/MS
View Answer
Explanation: In High pressure liquid chromatography, the B solvent used is HPLC grade organic solvent like acetonitrile, methanol with 0.1% acid. This acid is used for improving the shape of chromatographic peak and to provide source of protons in the reverse phase LC/MS.
7. Are these statements about the TFA (trifluoroacetic acid) in HPLC true?
Statement 1: It is commonly used as mobile phase additive.
Statement 2: It reduces the LC/MS signal.
a) True, False
b) True, True
c) False, True
d) False, False
View Answer
Explanation: TFA (trifluoroacetic acid) is a commonly used as mobile phase additive used in reversed phase HPLC separations of proteins and peptides. TFA restrictsconsiderablyto reduces the LC/MS signal, thus lowering the sensitivity.
8. What causes peak tailing?
a) Depends on the concentration of solvent
b) Occurrence of more than one mechanism of analytic retention
c) Depends on the concentration of solute
d) No occurrence of more than one mechanism of analytic retention
View Answer
Explanation: The primary cause of peak tailing is the existence of more than one mechanism of analytic retention. This is also due to analytic interactions with ionized silanols on the silica surface, which give rise to peak tailing. Therefore these interactions are to be minimized to achieve acceptable peak shapes.
9. Are these statements about the silica gel are used in TLC true?
Statement 1: It is widely used adsorbent and remains the dominant stationary phase.
Statement 2: The silanols are less acidic.
a) True, False
b) True, True
c) False, True
d) False, False
View Answer
Explanation: Silica gel is widely used adsorbent and remains the dominant stationary phase for TLC. The surface of silica gel has highest concentration of geminal and associated silanols is favored for the TLCas these silanols are less acidic.
10. Can negative peaks occur in HPLC?
a) True
b) False
View Answer
Explanation: A negative peak means that there is less absorbance while the peak is passing through the detector than when the mobile phase is passing through. It is due to the mobile phase which has more absorbance than the analyte at the monitored wavelength.
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