Q: Which equation correctly defines the Rf value in TLC?

$$Rf = \frac{\text{Distance travelled by compound}}{\text{Distance travelled by solvent front}}$$

Question 1

Which of the following best describes the principle underlying all chromatographic separations?

Accepted Answer

The partitioning of analytes between a stationary phase and a mobile phase

Question 2

In thin layer chromatography (TLC), what is the most common stationary phase used?

Accepted Answer

Silica gel

Question 3

A TLC plate is developed using a mobile phase with a high polarity index. What is the expected effect on the Rf values of the compounds?

Accepted Answer

Rf values for all compounds will increase

Question 4

Which equation correctly defines the Rf value in TLC?

Accepted Answer

$$Rf = \frac{	ext{Distance travelled by compound}}{	ext{Distance travelled by solvent front}}$$

Question 5

A pharmaceutical analyst is using TLC to check for impurities in a batch of hydrocortisone acetate. Which of the following best describes how TLC can be used for this purpose?

Accepted Answer

By comparing the Rf values and intensities of spots from the sample with those of known standards and impurities

Question 6

Which of the following is a non-destructive method for visualizing compounds on a TLC plate?

Accepted Answer

Ultraviolet (UV) light at 254 nm

Question 7

A mixture contains two compounds, A and B. Compound A has a higher affinity for the stationary phase than B. Which statement is correct regarding their migration on a TLC plate?

Accepted Answer

Compound A will travel a shorter distance than compound B

Question 8

Which of the following is NOT a limitation of TLC?

Accepted Answer

It is suitable for the analysis of volatile compounds

Question 9

A TLC experiment is performed using a silica gel plate and a mobile phase of ethyl acetate. If the analyst switches to a more polar mobile phase, what is the most likely outcome?

Accepted Answer

All compounds will have higher Rf values

Question 10

Which visualization reagent is most appropriate for detecting primary and secondary amines on a TLC plate?

Accepted Answer

Ninhydrin

Question 11

A pharmaceutical company needs to check for the presence of a 0.2% impurity in a batch of clotrimazole using TLC. What type of test is this?

Accepted Answer

Limit test

Question 12

Which of the following statements about the use of mixed mobile phases in TLC is correct?

Accepted Answer

Mixing solvents can achieve subtle changes in separation and resolution

Question 13

Which of the following best describes the term 'eluent' in chromatography?

Accepted Answer

The mobile phase used to move analytes through the stationary phase

Question 14

A TLC plate is visualized under UV light at 254 nm. What is the expected appearance of a compound that absorbs at this wavelength?

Accepted Answer

It will appear as a purple spot on a green background

Question 15

Which of the following is a real-world application of TLC in pharmaceutical analysis?

Accepted Answer

Detection of impurities in hydrocortisone acetate

Question 16

Which of the following best explains why TLC is unsuitable for volatile compounds?

Accepted Answer

Volatile compounds may evaporate before or during the separation process

Question 17

A TLC plate is run with a sample containing three compounds. The Rf values are 0.2, 0.5, and 0.8. Which compound is most likely to be the least polar?

Accepted Answer

The compound with Rf = 0.8

Question 18

Which of the following is a key advantage of TLC over other chromatographic techniques?

Accepted Answer

The entire chromatogram can be seen at once

Question 19

A pharmaceutical analyst is using TLC to identify an unknown compound. The Rf value of the unknown matches that of a standard under identical conditions. What can be concluded?

Accepted Answer

The unknown is likely to be the same compound as the standard

Thin Layer Chromatography (TLC) in Analytical and Pharmaceutical Chemistry

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