Dear All,
I am trying to pack semi-prep column (10x150 and 22x150). I tried several procedures but have the same results. Plate count is very good but "shoe" type of tailing observed on all peaks including neutral compounds (tailing at the bottom of the peak. I changed slurry and pucher compositions but have exactly the same problem. I think that it is something either mechanical or testing system related. I need advice from people who are doing same type of packing. I am packing regular C18 material and even tried bare silica with the same result. Any help is greatly appreciated.

MGS

What kind of column packer are you using?

I am using packer from unknown manufacturer and Haskel pump. Pressure around 500 bar (7500 psi). Slurry followed by different pusher. I have observed the same picture even when I change pusher and slurry compositions. For small columns I have no such problem. When I try to scale it up I run into problem.

What columns are you using?

I am using compression ring columns and columns from Alltech with appropriate adaptors.
I don't think that problem is in my solvent system (slurry/pusher), because I have packed analytical column (to test the procedure) with very good symmetry and plate count (symmetry close to 1 and 80,000 plates per meter)

If Prep column is compressed properly and the silica is Ok than only problem is your sample loading. what solvent u using for sample ?? in prep the sample loading is main cause for tailing. use less polar solvent for dissolution of sample and inject less amount in terms of conc and volumn and see the difference.

Hope this will help.

I am not familiar with this hardware, but many problems in prep are related to hardware.

You described the tailing as a shoe type. I have observed this type of tailing with certain stationary phases. The tail begins at about 1/10, or even lower, of the peak height and is as long as the peak width. I have observed this phenomena on preparative columns and in some cases on analytical columns too. This has happened on test chromatograms, using neutral aromatic compounds as analytes and 65% acetonitrile in water as the mobile phase. These columns have normally worked just fine in "normal life" applications.
I still haven't find the reasonable explanation for this behavior, so please if anyone have any ideas...

how many microns has the material you use in your semiprep columns?

I tried both 5 um and 10 um with different slurry and pusher combinations. My sample was dissoled in mobile phase and I tried to delute it several times to see the effect of concentration. Result was the same - "shoe" type tailing. Report shows symmetry of 0.95 9tailing factor of 1.05) with plate count of 75-80K plates per meter.

Your difficulties look familiar. We gave up with packing prep columns ourselves. We are now only buying prepacked prep columns.