Clean the column in normal phase LC

[thohry]

Hi all,
Normal phase HPLC is new to me. I just recently met the first one. The method uses a silica column and the mobile phase is methanol (with some additives) and pH is adjusted to 3.0 by HCl.
I am not sure how to clean the column at the end of the day. Can I use just pure methanol to clean the column or should I use some other solvents ?
Thanks

[tom jupille]

That depends on what the additives are and what they do. In general, you clean a column by flushing with a solvent tthat is stronger than the mobile phase. In this case, that would be water (or a water/methanol mix). The catch is that if your separation depends on having an additive adsorbed to the silica surface, you could be looking at long reequilibration times.

[mattmullaney]

Hello,

I guess that what you would choose as a column-cleaning solvent will kind of depend on what you are chromatographing. Methanol already is a pretty strong normal-phase eluent--think of it in the opposite terms of reversed-phase eluents. THF, IPA, IPA/chloroform or hexane are good for cleaning reversed-phase style modified silica--these are non-polar relative to water, ACN or MeOH, roughly speaking.

MeOH is far more polar than typically-used normal-phase solvents such as hexane, methylene chloride or MTBE, so in a fashion, MeOH would be a good strong eluent for cleaning. Water might be stronger still for polar analytes, but you don't want to mess with water levels on bare silica...whatever the case, make certain that whatever you choose to clean with is completely miscible with MeOH...your eluent of choice. IPA and acetone are great for converting between solvents of different polarity, should it come to that kind of thing...of the two, I've had better luck with IPA (acetone, depending on source, can have a lot of "junk" in it, even if it's supposed to be HPLC-Grade.)

Good Luck!! See what others may think. Tom's a faster typist than I am--and I agree with his comments. Tom, please pardon my tailgating!

[allene]

Be aware using water in nornal phase. Water is strongly polar solvent and adsorbed strongly to the silical surface and deactivates the silica staionary phase. So, I suggest you not use water for cleaning of silica column.

[thohry]

Thank you all for helping me.
I always thought silica column will adsorp H2O strongly so I may not use that. In case I try with H2O, do you think the column is still OK ?
Now , I will flush the column with MeOH and mix of MeOH with IPA (50:50).
Hope to hear other inputs

Regards

[mattmullaney]

I'd say to heed Tom's and Allene's warnings...while water may not "kill" a silica column completely off, you may find it will take a VERY long time to get the column back to a state where you're achieving repeatable analyte retention times. Doesn't take much water to "goof up" bare silica.

I'm kind of at a loss as to what you're silica column is holding on to...MeOH/IPA is a reasonable thing to try...I'm thinking that with MeOH as an eluent what you're retaining must be pretty polar stuff...Tom's suggestion in trying MeOH/water with just a little bit of water (say, less than 5% by volume) might be something to try, too. Just may take a Long Time to get the column back to performing the way it was before.

I'm hoping for you that the MeOH/IPA works out well! Best of Luck!!

[tom jupille]

The unasked question (so far) is "why do you want to clean the column?". If you're not seeing any problems, the best approach may be "if it ain't broke, don't fix it!".

[thohry]

The unasked question (so far) is "why do you want to clean the column?". If you're not seeing any problems, the best approach may be "if it ain't broke, don't fix it!".

I just follow the way when working with RP: running the column under 100% organic solvent for a while at the end of the day.

Thanks.