Chromatography Forum

Hi
I came across the term “Base Deactivated silicaâ€

To the best of my knowledge, the term refers to the process of metal removal from the silica particle surface. The advantage of the procedure is no positively charged metal ions on the silica surface = reduction of non-specific interactions.

Best Regards

Since you saw the term "based deactivated silica" in a RP column brochure, I believe it refers to "Type B" high-purity silica. Rather than removing metal contamination from the silica surface, type-B silica is made from very high-purity starting materials and stringent manufacturing processes. Absence of metal in the silica gel gives rise to lower silanol acidity, or improved peak shape for basic analytes. Surface metal contamination is rather easy to be removed using a chelating agent such as EDTA.

Hi XL,

I agree with you on the pure silica (type B) thoughts and all that.
But you don’t seem to provide the reason for the base treatment, bearing in mind the fact that you’re kind of disagreeing with my suggestion.
Not that I insist on knowing 100% the true reason for the base treatment in question, but I thought that was the reason (the explanation in my previous post).
So, now that I got intrigued, would you please tell us why would the manufacturers treat the silica particles this way?

Best Regards

Thermo offer information on Base Deactivated silica, Google found...
http://www.interscience.nl/promotiesite ... silbds.pdf.

Bruce Hamilton

Hi Danko,

In the contect of RP-LC, I believe high purity spheircal silica = type B silica = base deactivated silica (assuming we are talking about raw silica gel before bonding)

Base deactivated silica relates to "low silanol activity". Silanol activity is responsible for peak tailing of basic molecules at mid-pH and it is caused by the presence of metal contamination embedded in the silica substrate (introduced from the starting mateirals and the manufacturing process). Low metal contamionation means low silanol activity which means base deactivated. Thus cares need to be taken before and during the silica particles are formed, not after. In other words, process you mentioned to remove metal from silica surface won't be able to produce type-B silica if the starting materials used for making it have metal contamination. However, it is a common practice prior to silica bonding to ensue the quality of the bonded phase.

The term base-deactivated silica means absolutely nothing, with the exception that the company that is trying to sell you such a thing wants to tell you that such packings are suitable for the chromatography of bases - whatever that means...

A better and more meaning nomenclature is to differentiate silicas into high-purity silicas, commonly made from a tetraalkoxysilane, combined with using metal-free reagents and reaction vessels, and low-purity silicas, made from inorganic precursors such as water glass or similar that contain a more-or-less high level of other metal oxides, such as aluminum or iron oxide. The high-purity silicas became for the most part first available in the early 1990s, although materials of a reasonable quality existed already in the 1980s.

When you have a contamination of iron or aluminum in the matrix of the silica, this creates acidic silanol groups on the surface of the silica, and these acidic silanols are bad for basic analytes, i.e. create tailing. With a well prepared high-purity silica, this problem does not exist. Note that there is no way to turn a low purity silica into a high-purity silica, since the contamination is in the matrix.

Due to the fact that these older silica give tailing peaks for bases, there was in the late 1980s to early 1990s a trend to endcap these packings with an amino silane. When you do that, you can eliminate the tailing of basic analytes, but now you can't get acidic analytes off the column any more. Anyway, this may be the place where the name "base-deactivated silica" is coming from. However, today the meaning is rather fuzzy, and I suspect that many silicas are base deactivated by showing a bottle of base to the silica before starting the bonding reaction. Then the silica knows that it has been "base-deactivated" and will act accordingly.

I would tend to agree with Uwe that this is now a marketing term more so than a technical one.

The other consideration is that some manufacturers have altered the bonding structure to better shield the surface (bulky ligands, di-/tri-functional attachment, etc.). This leads to what could be called a "base deactivated stationary phase." The difference between stationary phase and silica could easily be lost on the person writing the marketing information.

But as noted above, it is more a description of performance than chemical structure.

Thermo offer information on Base Deactivated silica, Google found...

Bruce, was the information you linked to available in English as well? I don’t seem to be able to find it.

Best Regards

When WWW format rules and English grammar rules collide, the outcome is never good. Please remove the full stop from the end of the link, and all will be revealed. Sorry about that.

http://www.interscience.nl/promotiesite ... silbds.pdf

Please keep having fun,

Bruce Hamilton

Hi Bruce,

Thanks for the corrected link. I should have seen the dot at the end of the address - if I only paid more attention
Anyway, I think that was very valuable information.

Best Regards

Base deactivated silica -

Base = The "Silica" particle that makes up the stationary phase
Deactivated = The Base or Silica particle is deactivated towards secondary interactions (mixed mode) through techniques implied during production (controlling silanol content), extra dense bonding techniques and TMS capping.

Hi Mohan_2008,

Did you read the text Bruce was so kind to send a link to?
If not, it might be worth while spending 5 - 10 min on reading it.

Best Regards