Chromatography Forum

Hello Colleagues,

I am trying to pack DAC column (Dynamic axial compression) with regular (10 um) C18 bulk silica gel to scale up a method which was developed in our lab. All my attempts to pack 30x100 mm column failed due to low plate count (3000 plates/meter) and poor symmetry (0.5-0.6). I used some hints from Kromasil (even it is not kromasil silica):

http://www.kromasil.com/kromasil/opencm ... t/packing/

We see over 50K plates/meter on analytical column, so I was expecting at least 30K plates/meter on the prep column, but I am nowhere close. My silica, frits and tubing are new, so I have no idea what is wrong. Changing slurry composition had no effect on plate count and symmetry

Please help. My deadline is at the end of October and I need to do something fast.

Because your plate count test peak is fronting you could just have incorrect test conditions.

What is your mobile phase, flow rate, sample, sample concentration, sample diluent, and injection volume for your plate count test?
Usually I use a couple of compounds with different retention times since that eliminates several possible complications.

Things to check in your packing method:
1. Eliminating fines- Do a couple of sedimentations and pour off the supernatant.
2. Maintaining a well mixed slurry- Keep the slurry well mixed right up until you pour it in the column. Only do 1 continuous pour.
3. Fastest packing flow possible- The faster you pack the better the bed.
4. Removing air from the slurry- Degass the slurry, sonication/vacuum is probably best.
5. Wet the bottom frit with some solvent before pouring the slurry in.
6. Compress the bed as soon as possible after packing is complete.
7. Condition the bed with your normal flow rate and mobile phase until a steady pressure is reached.

Also was your analytical packing the same as your preparative packing? Shpherical/Irregular, distribution, and particle size.