Hi All,

Does anyone knows what is the high pressure limits of silica (C18 bonded) spherical particles stationarry phases? What is the maximum pressure that we can pack and work with? Is there a pressure after which the particles collapse? Consider that there are not limits from instrumentation point of view (special pump equipment etc.).

If you could also provide me with a reference that would be great.

Thanks

No Name,
I don't know but the answer might be with the developers of the Altex 100 if any of them are still with Beckman or Ranin might know, his engineers developed the pump. He said they built the pump to go to 20,000 psi but could not build seals to hold the pressure for more than a short time. I would guess that they might have been testing the limits of silica also. They thought the trend of 37 to 10 to 5 to 3 micron packing would continue and systems would require large pressures to get flow.
Jim

Hi no name, what particle size do you want to pack, what pore size, do you want to pack monodispers, or polydispers? What kind of surface chemistry do you have (bulk typ packing, brush type etc.)? Approx. back pressure for packing is 750 to 850 bar. Some materials require a slow increasing pack pressure, some a fast increasing back pressure, and so on. Just try under which back pressure you will get the best result. Check TP! First make your slurry and use high purity solvents.
Or buy a prepacked column from a column manufacturer. But make sure you purchase your column from a real manufacturer, who is also producing the basic silica, doing his own column chemistry, and is not just a "show" packing (marketing) company! Good luck. Gerhard

Hi Jim, hi Gerhard,

Gerhard: We already packing 150 micrometer capilaries columns with 2-3 micrometer (different lengths for each case) at 10000 psi (slow increasing back pressure) and operating at 5000-10000 psi without problems now.

We want to go higher, so starting wondering about possible problems and inherent limitations.

Thanks

There is a fair amount of published work in this area. Both Jim Jorgenson and Milton Lee have published articles relating to the use of columns at high pressure (and of course, of necessity this involves packing at high pressure too). For the most part, researchers have been using small (1.5 micron) nonporous particles when utilizing high pressures but if I remember correctly Milton Lee has done some work with porous particles in the pressure range you mention.

There is a section in my book on page 90 that covers this subject. In a single sentence, the relevant issue is the pressure per particle layer. This can be varied widely during packing.
From the standpoint of particle strength, the issue is strongly related to the specific pore volume of a packing. A packing like Spherisorb with a pore volume of 0.5 mL/g is indestructable under your conditions. A packing with 1 mL/g needs to be treated a bit more carefully, but from what you are describing, I would not worry about the strength of a 1 mL/g packing either.

Thanks Chris,

I'm aware for several of these groups published work but none of them (at least the one I have read) does not reply in my original question which was what is the high pressure limit of silica particles.

I was hoping that it would be maybe some old publications speaking about silicas particule pressure limits.

Thanks again

Just had your response Uwe, thanks for the info. When you say my conditions do you think it will be OK for 20000 psi as well?

Thanks

The real question is how fast you raise the pressure during the packing process. For a 1 mL/g packing, you may get into the critical range. On the other hand, Spherisorb and Nova-Pak are so hard, I would not even worry at 20 000 psi.