Silica type

[Daniel Martinho]

I have a confussion with Type A and Type B silica columns. Can you tell me if columns such as Symmetry (Waters), Luna(Phenomenex) or Prevail(Alltech) are Type B ?? (I think they are.....but then ...which columns are Type A ??). Thanks. Daniel.

[Uwe Neue]

I agree with you that the "type A" and "type B" nomencalture is confusing and therefore junk. Here is what it really means: you have high-purity silicas, which are derived from an organic silane such as tetraethoxy silane, and you have low-purity silicas derived essentially from sand.

"Type A" is the stuff that was around first, i.e. the older, low-purity silicas. Most "type B" (= high-purity) silicas are newer.

Symmetry and Luna are based on a high-purity silica.

[tom jupille]

There is a column selectivity database developed by Lloyd Snyder that lists around 300 columns, all characterized as "type A" or "type B" silica. I think a 60-day evaluation version is available as a free download from Rheodyne (click on the link in the sponsors section at the upper right of the screen), then follow the links for "Products . . . software . . . Column Match.

[Steve]

Type B should also have lower metal contamination and a higher pressure stability than Type A. Type B also allows for a better surface geometry of the particles (ie. more uniform shape). This allows for a better batch to batch reproduction of the columns in manufacturing.

That not to said the the older columns (Type A) are not good for seperation anymore.

[Uwe Neue]

The metal contamination of the silica has no impact whatsoever on the mechanical stability of a packing. The mechanical stability is determined by the specific pore volume of a silica. A packing with a low pore volume such as Nova-Pak (0.3 cc/g) or Spherisorb (0.5 cc/g) is much harder than a packing with pore volume of around 1 cc/g, as most of the more modern high-purity silicas have.

In addition, unless one wants to use a packing for UPLC, there is little concern about the mechanical stability of a silica.

There is also no link between the purity of a silica and the reproducibility of the packing made from it.

[Steve]

Uwe

I never intended to said that metal concentration has anything to do with stability. I all said, is that newer silica will contain less metal than the older Type A silica.

Addition, the newer Type B silica will have a better surface symmetry than the older silica. With this, Macherey-Nagel can place tighter controls on the particule size distrubtion that goes into the columns and has found a better batch to batch reproduction in manufacturing.

The purity of the silica does not provide for the reproduction, The new Type B silica is a better method to provide a more controlled and accurate particle size distrubition for the columns.

[irene_wu]

hi,
recently I read an article about the type A & type B silica column:
it said:
type A silica was used for most columns developed before approximately 15years ago. this silica was characterized by significant metal contamination and a very acidic surface. this resulted in badly tailing peaks for basic compounds and much larger column-to-column variability than we find acceptable today . the newer type B silica has a very low metal content and is processed in such a way that the surface is much less acidic than the older silicas. these columns are much more reproducible and , for the most part generate chromatograms with little or no tailing for basic compounds. author strongly believe that one should never start the development a new method on a type A column unless there are very compelling reasons.

[DR]

This is correct - the 'metal contamination' has an adverse effect on peak shape. Type B silica is used almost exclusively these days (some old type A columns are still on the market as a result of inertia/resistence to revalidating old methods). Any newer line of columns is almost certainly based on type B silica. The A/B debate is certainly dated at best (it's like comparing the merits of reel-to-reel vs. cassette tape after the advent of CDs).