Solubility of silica (silicon dioxide) in methanol

[Douglas Rodenburg]

What is the solubility of silica in methanol?

[tom jupille]

Considering that methanol is stored in glass bottles, I would have to say it's verylow (at least at room temperature). On the other hand, silica gel has much higher surface area than glass, so for silica it is probably non-zero. There must be published data on it somewhere, but I don't know where.

[chromatographer1]

I think the solubility might be highly dependent upon how much trace water is found in the methanol.

best wishes,

Rod

[HW Mueller]

It seems that the question of dissolution of silica by MeOH, even with some water in it, at neutral pH, is irrelevant to a chromatographer with an avarage lifetime.

[danko]

Hi Douglas,

I can only echo mr/dr Moeller’s reflection. But if you really regard potential dissolution of the silica stationary phase (or is it the support?) as a problem, just drop a spoonful of silica gel crystals in your mobile phase container and you won’t need to worry about that anymore.

Best Regards

[Douglas Rodenburg]

I agree with the slight dregree of the issue.
But what I want to know is

What is the number???? 0.001 mg/L, 0.000001 mg/L, at what pH, with or without water present, and so on?

Again, What is the number? or Where can I find it?

Thank you
Douglas

[chromatographer1]

Solubility of silica is 0.01 to 0.012% in water at pH = 8.0 at 25°C

The solubility of silica is methanol is probably not measurable or meaningful as Dr. Mueller has implied in his post.

reference:

http://pubs.acs.org/cgi-bin/abstract.cg ... sid=6006l3

The question is..................

how do you define zero?

best wishes,

Rod

[mbicking]

Sometimes it is comforting to know that all those books I kept on the shelf are still useful. So, without dating myself too much:

"The Chemistry of Silica," R. K. Iler, Wiley-Interscience, New York: 1979, pg 61-62. (This is the "silica bible" for classical silica information.)

1. "At 25 C, amorphous silica is essentially insoluble in methanol." But, the table reported that solubility was a strong function of water content. 10% water generated a solubility of 5 mg/L. 50% water generated 40 mg/L solubility.

2. Other researchers found that "silica gels dehydrated under optimum conditions and suspended in anhydrous alcohols" generated the following numbers:
methanol 1890 ppm
ethanol 164 ppm
1-propanol 8 ppm

When this book was written, modern LC silica particles did not exist. It seems likely that there will be differences with the type of silica (how it is made), and how it is treated before exposure. Particle size and pore size/structure will also influence some of these issues. And remember that all silicas will dissolve in basic solution, so if the methanol contains any strong bases (some organic bases are soluble in meoh), you could see a change.

In my experience, most LC columns are not affected by methanol, but it is somewhat more reactive than acetonitrile, so I would expect column lifetimes to be a little less. However, I doubt the differences would be very large.

[HW Mueller]

I tend to agree that there must be a considerable difference between silica used in columns and that which gave figures like 40mg/L for 50% water. If my reasoning is correct one would loose nearly 1/2 gram of a silica packing after passing a bit more than 10 L of this solution through. That amounts to maybe a 5 day lifetime of the column.
Or, could it be that there is a high kinetic barrier toward dissolution??

[Douglas Rodenburg]

Very Good!

Thank you Merlin.

There still is more to know such as pH, how anhydrous is "anhydrous", the impact of traces of water, time and temperature to saturation, and so on.

I suspect that while silica is soluable to 1890 ppm in anyhdrous methanol, somewhat aggressive conditions are likely necessary to achieve these concentrations. Conditions that are not normally used in LC.

[usv]

I'm a bit late posting a comment to this thread but I do have some additional observations and questions. In our organic lab, we have observed leaching of normal phase silica gel from colums during purifications run with high % methanol (e.g 20% Methanol in dichoromethane). With reversed phase-C18 media we observe that it too will leach into the eluant in high methanol applications (methanol/water). On a related note, we have experienced leaching of phase modifier from chiral stationary phases as well. All in preparative situations. I'd like to know if any of you have experienced this in an analytical situation.

[HW Mueller]

How did you determine that there was leaching, and what? How do you know that MeOH was doing the leaching?

[usv]

When collecting fractions in test tubes during chromatography, we have observedparticulates/cloudiness/turbidity in the eluent. This is not product. Typically see it when the mobile phase is at higher methanol percentages. We also see it in normal phase chromatography when running high methanol (which is less common).

[HW Mueller]

Could be that you flushed out fines of a cheap or mistreated column.

[usv]

Could be that - we have discussed that as a possibilty in the lab. Medium pressure and flash grade reverse phase silca vary vastly in particle size distribution. However, we do see it after repeated use of the columns too so I don't think that is the whole picture.