Longitudinal Diffusion Formula:
From: | To: |
Definition: Longitudinal diffusion is the contribution to band broadening in chromatography that results from the diffusion of analyte molecules along the column axis.
Purpose: This calculator helps determine the longitudinal diffusion coefficient (B) using the Van Deemter equation parameters.
The calculator uses the formula:
Where:
Explanation: The formula isolates the longitudinal diffusion component from the Van Deemter equation by subtracting the eddy diffusion and mass transfer resistance terms from the total plate height.
Details: Understanding longitudinal diffusion helps in optimizing chromatographic separation conditions and predicting column efficiency.
Tips: Enter all parameters from the Van Deemter equation. Plate height and velocity must be > 0, while eddy diffusion and resistance can be ≥ 0.
Q1: What is the Van Deemter equation?
A: The Van Deemter equation describes the relationship between plate height (H) and mobile phase velocity (u) in chromatography.
Q2: Why is longitudinal diffusion important?
A: It's one of three main factors affecting band broadening in chromatography, particularly at low flow rates.
Q3: What are typical values for these parameters?
A: Plate height is typically 10⁻⁴-10⁻³ m, eddy diffusion 10⁻⁵-10⁻⁴ m, resistance 10⁻³-10⁻¹ s, and velocity 10⁻³-10⁻¹ m/s.
Q4: How does mobile phase velocity affect B?
A: Longitudinal diffusion becomes less significant at higher velocities.
Q5: Can B be negative?
A: No, if you get a negative result, check your input values as this suggests an impossible combination.