silica Particle structure?

[rick1112]

I was browsing through certain catalogs and came up on image of silica particles ..(as shown in agilent cataloge)

The particles showed were like an agglomeration of microparticles…this was unlike the image that I had in my mind of smooth porous silica particles, which I thought are used in columns??

Also the recent post by Uwe Neue on Feb 27 in a thread
“Porous particles are essentially made by gluing nanometer-sized pebbles together. At least, this is the first step. One can vary the size of the "nano-pebbles" to change the pore size. Or one can dissolve and reprecipitate the solids to change the size of the structure and thus the size of the cavities in between.â€

[cyanogen78]

The silica particles you have seen in the Agilent catalogue is made in process of aglomeration of submicroparticles that process they call SIL-type and is patented by Agilent Technologies. All ZORBAX phases are based on such particles. In the catalogue Agilent give the benefits of their technology - there is something very logical in their statements. And the reliability of ZORBAX Series is well known. I heard that Thermo make their new sub-2micron phases with a similar technology. Most of the other vendors SOL-gel technology in which a final particle is of polymeric silica nethowork. I have worked with many different columns and some of them was very good. But probably when we talk about new sub-2micron phases it is more important which technology the manifacturer uses.

[Uwe Neue]

Silica has an impermeable backbone. Therefore the structure of the backbone is rather irrelevant (there is no such thing as a "polymeric silica network"). What counts for chromatographic performance are things like pore size, pore size distribution and then later the surface chemistry. The same things that can be prepared on one silica can also be prepared on another silica. The story about the "jolly gel" and the "silly gel" has no scientific merit.

[rick1112]

Hi

Does this mean that silica particle morphology doesn’t affect the column performance??

So irregular/uneven silica particles and smooth silica particles gives same column performance??

[Uwe Neue]

In the last statement there was nothing about the shape of the particles.

However, indeed, the performance of a column is very similar and - in the first order - independent of the shape of the particles.

[cyanogen78]

OK, Uwe, I agree with you for the silica structure, there is not such thing like "polymeric silica network" really. And the performance of a column depends on pore size, pore size distribution but also on particle size distribution and the packing quality (the homogenity of the packed bed), ok? Do you think that the statements of Agilent for the benefits of SIL-type technology (more rugged particles, less acidic and higher purity silica, more efficient control on particle size and pore size distributions) are commersial populism? I really find some logic esspecially for the more rugged particles because if this is true it will enable the manifacturer to pack the columns with higher pressures and probably this will ressult in better packed columns...I am interested which is true in fact

Disclaimer: the company I work for is a distributor of Agilent products.

[tom jupille]

Do you think that the statements of Agilent for the benefits of SIL-type technology (more rugged particles, less acidic and higher purity silica, more efficient control on particle size and pore size distributions) are commersial populism?

Since Uwe is employed by Waters, that's an unfair question!

[cyanogen78]

Since Uwe is employed by Waters, that's an unfair question!

I supposed that and may be the question is really unfair in this situation but if Uwe can state

What counts for chromatographic performance are things like pore size, pore size distribution and then later the surface chemistry. The same things that can be prepared on one silica can also be prepared on another silica. The story about the "jolly gel" and the "silly gel" has no scientific merit!

I am feeling free to ask for his opinion - is there comersial populism from Agilent? All I need is his opinion of experienced scientist and I will not comment it because Uwe has many more experience than me.

[Uwe Neue]

There is no such thing as a "sil gel technology" with the claimed advantages. The purity of a silica is a function of the raw material used to make the silica. A prime example of a very pure silica is Symmetry silica. The "ruggedness" of particles is primarily a function of the pore volume, and as far as I know the hardest fully porous particles in the world are Nova-Pak and Spherisorb, both based on lower purity raw materials. The pore size and pore size distribution can be controlled equally well with an approach that manipulates the size of the primary particles first or with the appraoch that makes the finished particle first and then changes the pore size. I would even argue that the secondary structure manipulation from the standard Ostwald ripening process is more likely to eliminate micropores than a process that starts with a preformed sol. Finally, for high-purity silicas, the acidity of surface silanols has something to do with the thermal history of the silica, and absolutely nothing with "sil gel technology".

[mbicking]

An interesting thread, especially the commercial marketing comments. You mean companies would actually stretch the truth a little to claim an advantage for their products? ... Shocking ...

I would hope that any posts to this forum, even from advocates, would include verifiable information, not marketing fluff. So, I welcome a healthy discussion, even if from people who have a relationship with the company/product being discussed. We are all scientists first, right?

Getting back on topic:
For a picture of a more conventional particle, look at: http://www.phenomenex.com/WorkArea/show ... x?id=11009 (page 2 compares the Zorbax and phenomenex particles). (Note: I do not have any relationship with Phenomenex, and do not currently use their products; this is just a relevent picture.)

[Uwe Neue]

A few additional comments on the Phenomenex brochure, this time in defence of Agilents Zorbax: the outer roughness of a particle is not a problem at all, and the fact that the Luna particles are smooth does not tell you anything about their performance as a chromatographic packing. The fact that Phenomenex found broken particles in the Zorbax packing only means that they unpacked a packed column. I can show the exact same thing for a Luna column. And, finally, Zorbax is a home-made silica by Agilent, while Phenomenex is does not have the particle technology to make Luna: they buy the unbonded silica from another vendor. There are not too many primary manufacturers around who can make the particles. Waters is making Nova-Pak, Spherisorb, Symmetry, XTerra, XBridge and other ones from the bottom up.

[mbicking]

Uwe, good points across the board, but you over-interpreted my post. I simply wanted to reference a picture of a "smooth" particle for visual comparison. I did not even read the Phenomenex discussion, so that's my mistake for not being more thorough.

Although I lack your extensive experience with these phases, I'm sure you would agree that the Phenomenex picture is more "typical" of most silica-based particles. I know it is similar to some Spherisorb material I worked with years ago.

But as you say, it 's the chromatography that matters! If it does the job, who cares what it looks like.

[danko]

But as you say, it 's the chromatography that matters! If it does the job, who cares what it looks like.

I completely agree. And while I think it’s nice to see what a silica particle looks like, it is not of much use to a chromatographer who’s interested in the performance in relation to a specific compound.
Having sad that, I think it helps to know that there are some differences, so that I won’t have to purchase a column that is exactly the same (just another name) as the one that didn’t work in the first place.
Regarding the particle shape, I’m not 100 % convinced that it does not matter.
Recently I had quite a challenging protein separation to achieve and following some testing of several columns/brands (although the same chemistry) that just separated the impurity as a shoulder to the main peak, I tested the Zorbax – Poroshell column (again the same chemistry C8 on silica) and there it was: Rs = 3 between these 2 peaks. It should be mentioned that everything else (mobile phase, equipment and chromatographic parameters) was the same.
So I attributed the superior separation to the particle shape, which was the most obvious difference between these columns. I realize that there could be a number of other, chemistry related factors, but as mentioned earlier, this particular column/brand/particle shape, worked beautifully and the task was completed.
I sure like to know which parameter made the difference, but it is quite a difficult investigation to undertake when one isn’t in the column manufacturing business.

So: Diversity long live – in every aspect of life

[Uwe Neue]

There can be a difference between a superficially porous particle such as the Poroshell and a fully porous particle. This is not what I meant about particle shape. When I was talking about particle shape, I thought about spherical versus irregular particles.

[cyanogen78]

Thanks a lot for the comprehensive answer, Uwe. You give me a matter for reflection...
As for the "smoothness " of Luna particles when compared to ZORBAX I think probably this is due to the process used to form the ZORBAX particle.
About the Poroshell - this packing is a "pellicular" with a solid core and a porous layer on the core all from silica as Uwe said. More about the benefits of this technology you can find here: http://www.advanced-materials-tech.com/halo.html. Basically better ressults that you had was due to the shorter diffussion path for the analyte molecules in these particles.
Finally I have one more question about the type of techology of forming silica particles - is there any signifficance about this when we talk about the sub 2-um particles that all of the leading suppliers offer? And which of two processes is used by Waters for example which is the main competitor of Agilent for LC columns (my opinion)?