Question 1

Which of the following is a key difference between classical liquid chromatography and High Performance Liquid Chromatography (HPLC)?

Accepted Answer

HPLC uses columns with a diameter in the mm range and steel material.

Question 2

In HPLC, what is the main function of the stationary phase?

Accepted Answer

To provide a high surface area for selective interaction with analytes.

Question 3

Which parameter is most directly related to the efficiency of an HPLC column?

Accepted Answer

Number of theoretical plates $$N$$

Question 4

A sample is injected into an HPLC system and produces a chromatogram with two overlapping peaks. Which parameter should be optimized to improve their separation?

Accepted Answer

Increase the selectivity factor $$\alpha$$ between the two analytes.

Question 5

Which equation correctly relates the number of theoretical plates $$N to $$the column length $$L$$ and the height equivalent to a theoretical plate $$H$$?

Accepted Answer

$$N = L / H$$

Question 6

A compound elutes from an HPLC column with a retention time $$t_R = 6$$ min. The dead time $$t_0 is 1 $$min. What is the retention factor $$k$$ for this compound?

Accepted Answer

$$k = \dfrac{t_R - t_0$}{t_0$} = \dfrac{6 - 1}{1} = 5$$

Question 7

Which of the following best describes the role of the mobile phase in HPLC?

Accepted Answer

It transports analytes through the column and enables partitioning between phases.

Question 8

In reverse phase (RP) HPLC, which type of analyte will have the longest retention time?

Accepted Answer

Highly hydrophobic analytes

Question 9

Which of the following compounds would be most suitable as a dead volume marker in normal phase chromatography?

Accepted Answer

n-Hexane

Question 10

The resolution $$R_s$$ between two peaks in HPLC can be increased by:

Accepted Answer

Increasing the number of theoretical plates $$N$$

Question 11

Which formula expresses the resolution $$R_s$$ between two peaks in terms of efficiency, selectivity, and retention factor?

Accepted Answer

$$R_s = \dfrac{N}{4} \dfrac{\alpha - 1}{\alpha} \dfrac{k}{k+1}$$

Question 12

A chromatogram shows a peak with a symmetry factor $$PS = 1.3. $$What does this indicate about the peak shape?

Accepted Answer

The peak is tailing.

Question 13

Which of the following is NOT a typical application of HPLC?

Accepted Answer

Measurement of atomic emission spectra

Question 14

If the flow rate in an HPLC system is doubled, what is the expected effect on the analysis time and resolution?

Accepted Answer

Analysis time decreases but resolution may decrease.

Question 15

Which property of the packing material in HPLC columns most directly affects the efficiency (number of theoretical plates $$N$$)?

Accepted Answer

Particle diameter $$d_p$$

Question 16

A student wants to separate a mixture of polar and nonpolar analytes using HPLC. Which combination of stationary and mobile phases should they choose for optimal separation?

Accepted Answer

Stationary and mobile phases with opposite polarities

Question 17

Which of the following statements about the retention factor $$k is $$TRUE?

Accepted Answer

It is zero for an unretained analyte.

Question 18

A chromatogram shows a single broad peak. Which of the following could be a reason for this observation?

Accepted Answer

Poor packing of column particles leading to band broadening

Question 19

Which detector type is commonly used in HPLC for compounds with chromophores?

Accepted Answer

UV-VIS detector

High Performance Liquid Chromatography (HPLC): Principles, Instrumentation, and Applications

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