Silica HIgh Temperature Stability?

[Alireza]

Hello everyone,

Does anyone have any idea how is the stability of silica ( Normal phase-Flash chromatography) at very high temperatures water? like 150 200 C ? just wanted to pack my own column and try in the oven at those temperature. Any suggestion ?

Thanks

[Uwe Neue]

Drying silica at these temperatures is not a problem.

However, you need to keep in mind that dry silica will pick up moisture again fairly easily, so your cooling procedure and your storage afterwards must be under controlled conditions and controlled timing.

[Alireza]

Maybe didn't explain quite well. My idea is hot water (flash- not HPLC) chromatography with silica packed column. I wanted to use hot water as the mobile phase and wondered how high can I go without losing its separation power.

[danko]

Alireza,

If you use water as a mobile phase with silica (i.e. NP chromatography), you won’t retain your compound/s anyway. Never mind whether it’s hot or not. By the way, why should flash make any difference compared to HPLC?

Best Regards

[Uwe Neue]

Sorry, I did not read your post carefully enough...

I agree with Danko: you will have a hard time to get anything retained on silica at 150 to 200 degrees Celsius with water as the mobile phase.

Second, it will change with time. I can't tell you how quickly, but I wouldn't give your column more than an hour or two. Conditions similar to waht you propose are used to enlarge the pores on a silica, which is essentially a dissolution/redeposition process.

You can potentially maximize the lifetime of your column by adding some acid. Dissolution is slower in acid. Silica can be cleaned by boiling it in mixtures of nitric and hydrochloric or sulfuric acids. I think that you can improve the stability of the silica best by adding acetic acid to your water.

BTW, how will you prevent your water from boiling?

[Alireza]

Dear All,

Thanks for your help so far,

danko,

1- The compounds that I'm working on are quite polar and I want to separate them from a more hydrophobic matrix, normal phase silica suggested quick elution of these compounds while retains other more hydrophobic compounds, and it works well with water. It seems a bit strange, but it works.

2- High temperature water is for removing the unwanted hydrophobic fraction, because it is pressurized in flash (3,4 bar) no problem in terms of boiling.

Uwe Neue
3- There are lots of studies on stability of silica based resins (like modified c18) at high temperature water. Just wonder if modified silica offeres better stability ( in terms of pore size or dissolution) compared to pure silica

[Uwe Neue]

It appears that you are relying on the rather weak hydrophobicity of the silica, which is due to siloxane bridges.

Since this interaction is weak, I have my doubts that you need a high temperature. On the other hand, why not remove the hydrophobically bound material with a bit of organic solvent, say methanol?