Chromatography Forum

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.

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.

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.

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.

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.

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.

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.

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).