DAC column packing problems

[moon704520]

one DAC HPLC column was packed
the column tube :50mmId
silica:280g,C4,10-15um,300A
packing pressue:750psi
slurry solvent:80%chloroform+20%IPA(per 1g silica added into 3ml slurry solvent)
after pouring the slurry into the column tube,the packing piston was pressed down by the packing machine ,the total packing takes less than one minute,and hold for more than 20 mins ,after that,the column was connected to the HPLC system to test the column efficiency,before injection at least three column volume testing mobile phase(50%ACN+50%H2O,the total pressureis 4.0Mpa) rinsed the column but the column efficiency is rather bad,seriously fronting???after packed the column bed out of the column tube,it is very hard to find anything unusual!can somebody help to explain?thanks
there is nothing wrong with the silica itself
i just want to know why the column efficiency is so bad??
is there anything I can do to improve?

[Uwe Neue]

Insufficient information!!!

DAC apparently means some kind of an axial compression column.
What did you do between the slurry solvent and the mobile phase?
Did I understand you correctly: your equilibration with mobile phase was about 3 column volumes?
What did you inject to test the column?

[moon704520]

What did you do between the slurry solvent and the mobile phase?


slurry solvent :80%chloroform+20%IPA
the testing mobile phase:50%ACN+50%H2O after finishing the packing,the column was connected to the HPLC system,then equlibration with the testing mobile phase

Did I understand you correctly: your equilibration with mobile phase was
about 3 column volumes?

you are correct

What did you inject to test the column?
the testing probe is benzene and naphthalene

[Uwe Neue]

I doubt that the slurry solvent and the mobile phase are completely miscible. Check!

An equilibration of 3 column volumes is not enough. Your peaks may be distorted because of immiscibility and lack of equilibrium. Of course, they also may be distorted because the column may be bad...

[Larry Miller]

My experience with DAC columns; when the packing is bad, there is peack tailing, not fronting. I agree the packing solvent and testing mobile phases are probably not miscible. I would flush with 4-5 column volumes of isopropanol (watch your column pressures) and then convert back to your testing mobile phase.

[moon704520]

thanks,my expeiment with the solvent prove you are right