Plugged columns!!!

[Dominique]

Hi! If someone could answer why I have this problem with different kinds of columns when mobile phases contain sodium salts of butanesulfonic or heptanesulfonic acid. I have used a Bondclone 10µ C18 with sodium butanesulfonate 0.006M with 5% methanol and the pressure kept increasing as weeks went by until I could not use it anymore and the same is happening with a second column.
Something similar happened when I used a Spherisorb ODS-2 3µ with sodium heptanesulfonate 0.03M with 5% methanol.
In both cases I used a flow of 2.0 mL/min and I also cleaned the columns after each and every run, first with water and then with a high proportion of organic solvent (acetonitrile in most cases).
I have tried washing them with 100% organic solvent at a low flow but the problem remains... Please help me...!

Dominique.

[Kostas Petritis]

I do not think that the salts are to blame (although 30 mM of heptasulfouric acid starts to be pretty high, are you sure is not 3 mM?). Probably the problem comes from what you inject (i.e. your sample; what is it by the way?).

[Dominique]

Hi!
I am analyzing medicines which do contain any number of excipients. I did consider that maybe some matrix component is retained in the column, but I have washed the column with tetrahydrofuran and it has made no difference, so I don't know what to think anymore. I'm afraid to damage the column beyond repair if I go more hydrophobic with the solvents... And yes, I also thought that the salt concentration of 30 mM was terribly high plus i forgot to mention that this mobile phase also has orthophosphoric acid and triethylamine. I don't have much liberty for method development and modifying, but i do try to take care of my poor columns as much as I can.

[Bruce Hamilton]

I think I would try flushing the columns initially with a water/acetonitrile mix that you know all of your sample components are soluble in, rather than pure water. I would also still go to the high acetonitrile flush, but perhaps even initially with a little acid to help move junk along.

I assume you are using HPLC grade reagents, if not - you should consider filtering the mobile phase, and perhaps filtering or centrifuging your samples. I would also invest in a guard column, if you're not already using one.

Please keep having fun,

Bruce Hamilton