Chromatography Forum

Hi

I wanted to pose a question to the forum. We are familiar with mixers that are sold for the purpose of mixing mobile phases together. Most of these that I've seen are the static shear mixers. I was just curious why people don't use glass bead columns for this purpose. As I understand it the shear mixers primarily mix radially, whereas the glass bead columns can mix both radially and longitudinally.

We are undertaking a research project and (without sharing too many details) we are looking for something that would mix both radially and longitudinally; and of course without too much band broadening. A tall order, I realize.

Any suggestions on different methods of mixing, and the advantages and disadvantages or each (or any publications that discuss this) would be of interest.

Thanks very much in advance!

if you mix two things together in any tube with length, then longditudinal mixing "smooths" the result. It means that if I set up a pump to jump abruptly from 10% to 30%, the actual result climbs more slowly because the 30% front introduced at the start of the mixer is being mixed longitudinally with content that is still 10%.

In general, HPLC users expect their pump to produce what it says it's producing. If they want a smooth climb, they will specify it. If your pump doesn't respond immediately, it will give different results to other, existing systems, that do. That's not a desirable characteristic.

Low mixing-volume is another serious consideration. If you are running at 400uL/min and want to do UPLC-style methods with run times of only a minute or two, a mixer with a 400uL volume would add 50% or more to the run-time. Of course a mixer that also "smooths" over 400uL would be incapable of pumping a 1-min gradient method at 400uL/min because the entire gradient would fit in the mixer at one go and could be smoothed to oblivion.

Many many years ago some colleagues of mine did something with this - if I recall their plan was to create a gradient in a packed tube and then pump it out into the separating column. Details elude me but I do not recall that it was a resounding success. If they published it Victor Pretorius would have been one of the authors.

Peter