Column Equilibration Formula

[pilger]

Hello

We are using 0.05M NaOH as an eluent as we are finding the equilibration time to be around 180 minutes. PA20 column and this is going from a flow rate of 0.05ml/min to 0.5ml/min.

Is there a formula that can be used to calculate this? The point being that we would like to play with different column sizes and flow rates to shorten this equilibration time from 180 minutes to less than 30 minutes.

Regards

[Hollow]

Hi

Just calculate the volume pumped (Flowrate*time)+ and divide it by the colum-volume (r^2*pi*L*)++
Keep that ratio the same for new column dimensions.
Then calculate the time needed for a certain flowrate.

+: if you ramp up the flow, take this into account: draw a chart flowrate vs. time and calculate the area under the curve
++: the true column volume will be a fraction of that (inter particle volume) but for a short approximation and scaling the geometrical volume will do the job.

Are the 180 min experimentally determined or just general procedure?
I would ramp the flow relativley fast to the needed flow rate then equlibrate with this flowrate until the needed volume has been pumped.
You may also test how much equilibration is needed by making injections of a test mix in the same solvent and see if retention time doesn't change between two consecutive injections.

[vmu]

the true column volume will be a fraction of that (inter particle volume)

To clarify: the column hold-up (void or dead) volume will be a fraction of that (interparticle volume + intraparticle pore volume).

[Hollow]

the true column volume will be a fraction of that (inter particle volume)

To clarify: the column hold-up (void or dead) volume will be a fraction of that (interparticle volume + intraparticle pore volume).

Yes you're right.
I took a shortcut in that the PA20 are pellicular particles, so that I guess the intra-pore volume will be small (but of course not beeing zero)