Is it true that solid core gives lower pressure?

[Mattias]

An example from today:

- I am running a method with a Waters XBridge C18, 3.5 µm at 0.8 ml/min (3.0 * 150 mm). This gives a backpressure of 2200 psi.

- Installed a Kinetex C18, 2.6 µm (3.0 *150 mm). All parameters are the same. With this column I get 2200 psi at 0.4 ml/min.

It is not the same particle size of course, but I have a feeling that Phenomenex is exaggerating the reduction of backpressure?

[bunnahabhain]

They do not exaggerate: Try the online calculator at https://www.phenomenex.com/tools/kinetexcalculator#

The result with your input data is: 151.7 bar at 0.8 mL/min (Xbridge 3.5 µm) vs. 179.98 bar at 0.4 mL/min (Kinetex C18).

According to this tool, the separation should increase dramatically when using the same column dimensions - to get some benefit out of the Kinetex, you could use a shorter column: This would reduce analysis time and solvent consumption maintaining the efficiency of separation.

[HPLCaddict]

Remember that backpressure depends on the particle size squared (!) so even a modest change in particle size (such as from 3.5 to 2.6 µm) will have quite an impact on backpressure. In your case, changing from 3.5 to 2.6 µm will increase the backpressure 3.5^2/2.6^2 = ~1.8-fold. This is a basic physical principle that is independent of the particle morphology (fully-pourous vs. core-shell). So a 2.6 µm particle will always generate a much higher backpressure than a 3.5 µm particle, no matter if it is fully-pourous or core-shell.

Concerning the reduction of backpressure, this claim is true - if you compare particle sizes which give roughly the same efficiency. So it would be fair to compare the 2.6 µm solid-core with a 1.7-2.0 µm fully-pourous - the core-shell column will give you roughly the same efficiency at a MUCH lower backpressure.

[Mattias]

Thanks for your replies!

The calculations of backpressure seems to fit with the data at least I might have misunderstood the point of solid-core. So if I could buy a 2.6 µm XBridge material, I would get the same backpressure as on the Kinetex column but (in theory) higher plate counts?

In this case, analyzing a badly behaving peptide, the XBridge column won on all parameters. Despite using 0.1% TFA in the mobile phase, I got a tailing factor of 2.6 on the XBridge and almost 4 on the Kinetex column. The plate counts was consequently higher on the XBridge as well.

[tom jupille]

So if I could buy a 2.6 µm XBridge material, I would get the same backpressure as on the Kinetex column but (in theory) higher plate counts?

. No, given the same particle size, a solid core packing should give a higher plate count, assuming there are no ”chemical” problems like tailing.