C18 columns - why so different?

[zhi ju]

I have used water Symmetry C18 column and run with 5% formic acid as A solvent for a long time.

Why is Discovery C18 not allowed to run with any formic acid. If run, what will be resulted in? Column collapse and how to save? Who knows?

[Victor]

Who gave you this recommendation not to run a Discovery C18 column in formic acid?

I never heard of this.

[syx]

How could a column 'be collapsed' due to acid mobile phase?

[zhi ju]

1. From column sheet, it point out not to use strong acid such as formic acid, HCl etc.

2. I called the company and he said even not to use pure water, at least 20% methanol in water. The strong acids and 100% water could result in collapse of column fillings.


I am really confused. Last five years I alway used pure DI water to clean system and columns. Why does water make trouble too towards C18 column. Really, from a literature it said not using 100% water to C18 column. Please put your knowledge!!

[Noser222]

I would expect that your column sheet means that you should not run concentrated formic acid. Diluting it to give you a pH in the typical operating range should be fine.

[adam]

The issue of phase collapse with 100% water and problems with concentrated acid have already been addressed by other posts.

With respect to the comment about cleaning with Pure DI water. This is defenitely *not* the way to clean any kind of reversed phase column. This will have the opposite effect, causing junk to accumulate.

[MG]

DI water will remove buffer salts, however.

[Uwe Neue]

I think a few words of clarification might be useful.

When very hydrophobic C18 columns are operated in a mobile phase containing close to or at 100% water, you can suddenly loose retention. This has been called "phase collapse", but it is better described as a dewetting phenomenon. The column is not damaged, though. Simply washing it with a milliliter or two of an organic solvent such as methanol or acetonitrile restores the retention.

A reversed-phase column is not cleaned by water. However, one can use water to remove salts prior to storage of the column. Storage is best done in 100% acetonitrile to prevent slow hydrolysis during storage. A good way to wash out salts is to use 80% water with 20% organic. Then there is no concern whatsoever about dewetting.

How stable a column is under acidic conditions depends on the column chemistry. It is the pH that is important, not the type of acid. Monofunctionally bonded columns should not be used below pH 2, multifunctionally bonded columns can be used at a lower pH.

I do not see a problem with using formic acid. Hydrochloric acid is generally not recommended with a standard HPLC instrument. This is not a problem with the column chemistry, but with the steel of the HPLC instrumemt. We have used HCl without trouble in metal-free systems with metal-free columns.

[zhi ju]

Great writing!