Q: What is the main disadvantage of using totally porous silica particles in HPLC at pH < 3?

Silica degradation by hydrolysis

Q: A chromatogram shows two overlapping peaks. Which parameter should be optimized first to improve their separation?

Increase the separation factor $\alpha$

Q: Which equation best describes the resolution $R_s$ in HPLC?

$R_s = \frac{N^{1/2}}{4} \frac{\alpha - 1}{\alpha} \frac{k}{k+1}$

Question 1

Which parameter, when increased, most strongly improves the resolution $R_s$ in HPLC separations according to the provided graph?

Accepted Answer

Separation factor $\alpha$

Question 2

In systematic HPLC method development, what is the effect of increasing the plate number $N$?

Accepted Answer

It narrows the peaks, improving resolution.

Question 3

Which of the following changes would most likely decrease the retention factor $k$ in RP-HPLC?

Accepted Answer

Increasing the organic solvent content in the mobile phase

Question 4

A chromatogram shows significant peak tailing for a basic analyte in RP-HPLC. Which modification to the stationary phase would best address this issue?

Accepted Answer

Endcap the stationary phase to reduce free silanol groups

Question 5

Which type of HPLC particle provides sharper peaks and higher detection sensitivity for high molecular weight analytes?

Accepted Answer

Superficially porous particles (core-shell)

Question 6

Why are polymer-based packing materials preferred for HPLC separations at extreme pH values?

Accepted Answer

They are compatible with a wider pH range and do not degrade by hydrolysis

Question 7

Which stationary phase modification is most effective for improving peak shape of basic analytes in RP-HPLC?

Accepted Answer

Endcapping with short alkyl residues to reduce silanol population

Question 8

A peptide mixture is analyzed by RP-HPLC using 25% methanol in the mobile phase. Which peptide will elute first?

Accepted Answer

The peptide with the lowest hydrophobicity

Question 9

What is the main disadvantage of using totally porous silica particles in HPLC at pH < 3?

Accepted Answer

Silica degradation by hydrolysis

Question 10

Which factor primarily influences the retention factor $k$ in RP-HPLC?

Accepted Answer

Mobile phase composition

Question 11

A chromatogram shows two overlapping peaks. Which parameter should be optimized first to improve their separation?

Accepted Answer

Increase the separation factor $\alpha$

Question 12

Which equation best describes the resolution $R_s$ in HPLC?

Accepted Answer

$R_s = \frac{N^{1/2}}{4} \frac{\alpha - 1}{\alpha} \frac{k}{k+1}$

Question 13

Which packing material would you select for high pH stability and improved peak shape for basic analytes?

Accepted Answer

Hybrid silica-based materials

Question 14

What is the main reason for peak tailing in RP-HPLC when analyzing basic compounds?

Accepted Answer

Interaction with residual silanol groups

Question 15

Which of the following is a benefit of using superficially porous (core-shell) particles in HPLC?

Accepted Answer

Shorter diffusion paths and sharper peaks

Question 16

If you need to separate a mixture of zwitterionic peptides, which stationary phase would be most suitable?

Accepted Answer

Specialized phases for ionic/zwitterionic analytes

Question 17

Which factor does NOT primarily influence the column efficiency (plate number $N$) in HPLC?

Accepted Answer

Mobile phase composition

Question 18

A student wants to improve the resolution between two closely eluting peaks in RP-HPLC. Which strategy would be most effective?

Accepted Answer

Change the stationary phase to alter $\alpha$

Question 19

Which packing material is most likely to degrade at pH > 7.5 in HPLC?

Accepted Answer

Totally porous silica particles

Question 20

Which of the following is a key advantage of endcapping in RP-HPLC stationary phases?

Accepted Answer

Reduces peak tailing by minimizing free silanol groups

Instrumental Analysis: HPLC Method Development and Stationary Phases

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