Question

Arrange the following band-broadening contributions in LC (Liquid Chromatography) from those most reduced by decreasing particle size to those least affected. A. Eddy diffusion
B. Longitudinal diffusion
C. Mass transfer resistance
Choose the correct answer from the options given below :

• A. A $\rightarrow$ C $\rightarrow$ B
• B. C $\rightarrow$ A $\rightarrow$ B
• C. A $\rightarrow$ B $\rightarrow$ C
• D. B $\rightarrow$ A $\rightarrow$ C

Hint:

Van Deemter: A (eddy) most affected, C (mass transfer) moderate, B (longitudinal) least by particle size.

Answer 1

The Correct Option is A

Concept: Band broadening in chromatography is described by the Van Deemter equation, which includes three main contributions:
• Eddy diffusion (A term)
• Longitudinal diffusion (B term)
• Mass transfer resistance (C term) Particle size of the stationary phase significantly affects these terms.

Step 1: Eddy diffusion (A).
Eddy diffusion arises due to multiple flow paths in packed columns. Smaller particle size reduces path variability and improves uniformity of flow paths.
Thus, eddy diffusion is most strongly reduced by decreasing particle size.

Step 2: Mass transfer resistance (C).
Mass transfer refers to the time required for analyte molecules to equilibrate between mobile and stationary phases. Smaller particles reduce diffusion distance and improve mass transfer efficiency.
Thus, moderately affected by particle size.

Step 3: Longitudinal diffusion (B).
Longitudinal diffusion depends on molecular diffusion along the column axis and is mainly influenced by time and flow rate rather than particle size.
Thus, least affected by particle size.

Step 4: Forming correct order.
\[ \text{Most affected} \rightarrow \text{Least affected: } A \rightarrow C \rightarrow B \] Final Conclusion:
Hence, the correct answer is option (1).