# How do I determine column void volume? - WKB28079

## ENVIRONMENT

- HPLC column
- UPLC column
- Void volume
- reverse phase
- normal phase

## ANSWER

For columns with fully porous packings, use the formula pi * (r)^{2 }* L * 0.66.

For columns with superficially porous packings, use the formula pi * (r)^{2 }* L * 0.49.

## ADDITIONAL INFORMATION

This information is useful for chromatography methods involving a retentive mechanism like reverse phase or normal phase.

The formulas shown above merely reflect an estimate of the void volume of a packed column (interstitial volume plus the pore volume).

To understand what the actual column void volume is for a particular column installed on a particular system, you must make an injection with a compound that does not retain on the packing material. Once a void marker peak is injected, you can use the following formula to determine column void volume:

Retention time of void peak (V_{o}) * Flow Rate

Example: If an acetone peak retains at 2.32 min, and the flow rate is 0.85 mL/min, then:

V_{o} = 2.32 min * 0.85 mL/min

V_{o} = 1.972 mL

Also see --> How do I calculate the empty column volume of a column?