Flow Rate Converter

This converter translates between volumetric flow rate (volume per time) and linear flow rate (distance per time) for chromatography columns. Understanding both flow rate types is crucial for optimizing separations, ensuring consistent performance across different column sizes, and successfully transferring methods between labs.

The Relationship Between Flow Rates

The linear flow rate (or linear velocity) represents how fast the mobile phase travels through the column bed. It's related to volumetric flow rate through the column's cross-sectional area:

Where $u$ is the linear flow rate (cm/h or cm/min), $Q$ is the volumetric flow rate (mL/min or L/h), and $A$ is the cross-sectional area of the column (cm²).

The cross-sectional area is calculated from the column diameter:

Where $d$ is the column diameter. This shows that doubling the diameter quadruples the cross-sectional area, requiring four times the volumetric flow rate to maintain the same linear velocity.

Why Linear Flow Rate Matters

• Residence time control: Linear flow rate directly determines how long molecules interact with the stationary phase, affecting separation quality
• Method transfer: Maintaining the same linear velocity when switching column diameters preserves separation characteristics
• Resolution optimization: The van Deemter equation shows that resolution depends on linear velocity, not volumetric flow rate
• Consistency: Linear flow rate normalizes performance across different column geometries, making comparisons meaningful

Practical Applications

This converter is essential for:

• Scaling chromatography methods from analytical to preparative columns
• Transferring methods between different column diameters while maintaining separation performance
• Optimizing flow rates to achieve target residence times
• Converting flow rates specified in literature to match your equipment
• Process development and scale-up in biopharmaceutical manufacturing

Example

If you run an analytical method at 1 mL/min on a 1 cm diameter column, the linear flow rate is approximately 76 cm/h. To maintain the same separation on a 10 cm diameter preparative column, you would need 100 mL/min volumetric flow rate to achieve the same 76 cm/h linear velocity.