Chromatography Forum

Hello all,

I calculated the total volume of my column. But, Im not sure to calculate the stationary phase volume and mobile phase volume. I'm using 3.0 * 150 mm * 3.5 microns.

Thanks,
Sree

Do you want to *calculate* it or *estimate* it?

If you want to estimate, for reversed phase columns the volume of mobile phase (Vm) is approximately 0.5 x L x dc^2 where L is the column length and dc is the column ID. This is usually correct within about +/-15% or so.

If you want to calculate, you can't; you have to measure the dead time (t0) and then multiply by the flow rate to get Vm. Getting an "accurate" measure of t0 is itself a complicated issue; for example this discussion from the early days of the Forum:
http://www.lcresources.com/discus/messa ... 3/215.html

I was not correct. I need to estimate.

http://people.rit.edu/pac8612/webionex/ ... e4o85.html

I was bit confused after seeing the above link. Thanks Tom.

Agilent typically states 0.6 x the column radius squared x pi x length due to stationary phase particles

The Agilent equation gives the volume of the support - isn't the stationary phase strictly the almost monomolecular layer of e.g. C18 stuck onto the surface of the support ?, or even more strictly still the "outer" surface of the layer, which is the only bit that the analytes get to see ?

Ah the simple joys and geometry of capillary GC

Peter