Question

The "Van Deemter equation" describes the elements of band broadening and chromatographic column efficiency in terms of
(A). Eddy diffusion of analyte in the column
(B). Longitudinal diffusion of analyte in the column
(C). Mass transfer of analyte between stationary and mobile phase
(D). Flow rate
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A), (B) and (C) only.
• C. (A), (B), (C) and (D).
• D. (C) and (D) only.

Hint:

Remember the three terms of the Van Deemter plot: \(A\) (path variance), \(B\) (diffusion over time), and \(C\) (equilibration lag). All three directly represent physical mechanisms of band broadening.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The Van Deemter equation is used in chromatography to describe the physical factors that lead to peak dispersion or band broadening inside a column.

Step 2: Detailed Explanation:
The mathematical statement of the Van Deemter equation is: \[ H = A + \frac{B}{u} + C \cdot u \] where: - \(H\) is the height equivalent to a theoretical plate (HETP), representing column efficiency.
- \(u\) is the linear velocity of the mobile phase (flow rate).
The terms contributing to peak dispersion and band broadening are: 1. \(A\): Eddy diffusion (or multiple path term), representing variation in flow paths (A).
2. \(B\): Longitudinal molecular diffusion, describing the axial diffusion of the analyte along the column (B).
3. \(C\): Mass transfer resistance, describing the finite time required for the analyte to equilibrate between the stationary phase and the mobile phase (C).
While flow rate (D) is the primary variable, the three physical *elements of band broadening* in the column are the Eddy diffusion, Longitudinal diffusion, and Mass transfer terms.

Step 3: Final Answer:
Therefore, the physical elements of band broadening are represented by (A), (B), and (C), making option (B) the correct choice.