How to generate normal phase LC column

[thohry]

Hi all,
Our Si column start to give bad peaks and the baseline is drifting , perhaps there's water inside. How can I improve the situation. I rarely use normal phase.
Thanks for any help.

[M Farooq]

You can wash the column with IPA and re-switch to normal phase mode.

If it is a bare silica column, don't be surprised by poor or different performance after storage in inappropriate storage solutions.

[uzman]

Ethyl acetate washing is highly recommended , then swith to hexane or iso-octane.

[thohry]

Thank you both for the suggestions.
I will try it.

[HPLCaddict]

I'd also go with isopropanole first. Water-insoluble solvents such as ethylacetate, hexane or octane will lead to problems if there really is water in the column.

[uzman]

Dear HPLCaddict,

Ethyl acetate is highly miscible with water ( 8.3g / 100 ml @ 20 C )

[thohry]

By the way, in case I have a new NP column, what solvent(s) should I use to activate before using it ?
Thanks

[HPLCaddict]

Dear HPLCaddict,

Ethyl acetate is highly miscible with water ( 8.3g / 100 ml @ 20 C )

You'd call that "highly miscible"? Look at any solubility table, it will tell you that ethyl acetate and water are deemed to be immiscible. And it's 8.3g of ethyl acetate in water, not the other way round
Water has a VERY high affinity to silica, with ethyl acetate you'd have to flush the column for ages to get rid of it.

[Andy Alpert]

Per HPLCaddict's observation:

Welcome to the origin of the HILIC concept...

[uzman]

HPLCaddict ,

Regarding miscibility of ethyl acetate with water , you are right , they are not miscible , they are soluble to some percentage , sorry about my poor english

The point is , ethyl acetate is highly miscible with water , THAN hexane ( 1mg / 100 ml ) or ıso-octane , so it is a good washing solvent for pure silica columns.

Alcohols also have a high adsorbtion to silica , like water , and they may deactivate the silica , so I avoid using them.

[Hollow]

I once read a publication where they used 2,2-dimethoxypropane (=acetone dimethylacetal) to "reactivate" a wet silica column. The DMP will react with any water around to give acetone and methanol.