Chromatography Forum

the initial search looks like everyone is using it for plasma/protein sample cleanup,
anyone knows how it behaved for medicinal compounds separation, compared to C18 RP HPLC?
and who sell the column/particles, anything specific to the routine reversed phase LC running?
any pointer to websites/resources will be aapreciated.

smiley,

As far as I know the only company selling columns for turbulent flow chromatography is Cohesive Technologies ( http://www.cohesivetech.com/ ). I'm not terribly familiar with their product line but I believe they may have some products for the applications you propose.

Off the top of my head, the whole idea of turbulent flow chromatography is aimed more at larger molecules. The intent is improved mobile phase mass transfer kinetics. In order to get up into turbulent flow with "reasonable" pressures, fairly large particles are used. Bottom line is you get a fairly low plate count, but you get it in a very short time.

If you are dealing with "clean" samples then try simply winding your flow rate up. Generally you will need to decide whether the trade off between rapid analysis versus shorter column life is worth it for what you are doing. I've seen this approach used successfully for clean ie none biological samples on several occasions. Flow rates way beyond the norm for a column give suprisingly good results without massively reducing column life. As Tom says I've only really seen turboflow used with samples of a bio nature.

thanks everyone,
yes, i am looking at the possibility with "clean" samples, since the speed is more critical than column life, etc.
have talked with Cohesive but the saleperson is not very good at science, my question is is it comparable plate counts with regular hplc, and with most small molecules? and what about the loading in prep mode.
the data from Cohesive shows a sharp peak of DMSO, instead of broad one in routine hplc, this is where i am interested.
any thoughts?

Are you doing prep or analytical?

Analytical plate count is (in principle, not direct experience) substantially lower than typical HPLC.

For prep, plate count may be less important than loading capacity. I would expect that to be similar, but that depends on the detailed chemistry of your samples.

You have to be careful to evaluate peak sharpness in volume terms, not time. Turbulent flow kicks in at much higher flow rates, so even a low plate count (broad) peak can look sharp on a time axis.

On the risk that I am getting a letter from a lawyer who will tell me to shut up:

There is nothing turbulent in turbulent flow chromatography. It is very-high-flow-rate chromatography executed on very large particles. Under these circumstances, large molecules such as proteins do not have enough time to penetrate into the pores and they are washed out of the column without trouble, while small molecules that diffuse faster will get into the pores of the packing and stick there. Furthermore, this is helped by a pore size that lets small molecules in but keeps large ones out.

Considering that you use large particles, you will not get the performance that you would get from small particles. Most of the Cohesive applications that I remember are based on very rapid gradients, often step gradients. Separation performance is not the issue nor the strength of these large particles.

On-line sample preparation with large particles is performed by Waters as well. We use smaller particles than Cohesive, because the patent says that you need particles above 30 micron to get "turbulent flow". Cohesive uses 50 micron particles, we use 25 micron particles.

Uwe, thanks for a clear, cogent explanation (and we promise not to tell the lawyers!)

There was also PerSeptive Biosystems (bought/merged by/with??) with their POROS polymer phases, they used a different term, "Perfusion Chromatography", for the same thing, apparently (also patented).

....thought we agreed (in a similar discussion) that all columns have turbulent flow, or was it non-laminar flow??

"Perfusion chromatography" is related in that it's an attempt to improve mass transfer kinetics. That technique uses particles which have "through" pores, so that some portion of the mobile phase flow goes through the particles rather than around the particles. In effect, this makes the particles look smaller than they really are (in terms of diffusion distances).

On the laminar vs turbulent flow, I've always assumed that HPLC operated pretty much under laminar flow conditions, but I don't know enough hydrodynamics to justify that assumption!

All that I could ever clear from the info given by those manufacturers is that the pores are larger.
On laminar flow: Not going through the material at my disposal, which I have not yet "digested" anyway, it seems that, mathematically, normal columns don´t have turbulent flow, but I can´t see how it could be laminar. Where is Uwe?