Chromatography Forum

Hi

Recently I was came across varian columns with 3 different particle size :- 3um, 2.8um and 2.4um..i was just wondering what is the advantage of such sample variation in particle size e.g the difference between 3um and 2.8um is just 0.2um..what added advantage could this bring in???

Also When I looked other sub-2um and 2um columns from different vendor I found out an array of number like ZORBAX offers 1.8um column ,Waters Acquity columns are available in both 1.7um (BEH column ) and 1.8um (HSS column) ?? so why is there so much difference in particle size?? And how do one arrive at these values??

Thanks a lot

hi

was just wondering have i asked the question in too confusing way.. ?? (sorry if i have..) or it one of those questions which doesnt have a Definite answer..

There is no standard yet in the sub-3 and sub-2 micron so the different companies can come with whatever they feel like. Most of the time it will depend on what is easier for them to achieve during the synthesis. Especially for smaller particle sizes it becomes a challenge to produce narrow particle distributions...

Depending on how and on what instrument you use to measure the particles size, the result can vary. I learned from one of the conferences I attended that almost all sub-2-um paricles columns were packed with larger than 2-um particles based on SEM. Small particle size and high plate count don't always correlate. I came across a so-called sub-2 micron column which gave a efficiency merely marginally better than a 3-micron column. Therefore, I recommend forget about particle size, and focus on the column performance such as efficiency, peak shape, and more importantly selectivity.

Traditional laser based particle size systems use laser diffraction to measure the particle size. The size given assumes that the particle is opaic and spherical. Silica partcles allow light to pass through them so are very difficult to measure. The ideal would be to measure each particle by SEM and to sort by hand to get the exact sizes. Might make columns very expensive Instead the manufacturers set up their manufacturing process to make particles of a certain size and QC batches using laser diffraction instruments. The results will show a particle distribution around the stated size. The best columns are likely to have the most uniform sizes of particle. You should not assume that when buying a column of 2.4um particles that these will actually be that size or even that they really are smaller than a manufacturer that claims 3um particle size. Laser diffraction does not give accurate results below about 10um id and you are lucky if it even gives you reproducable results at that particle size. The laser used is a red laser of wavelength about 670nm far to close to the size of a 3um id particle.

It is better to chose your column based on the actual performance on a standard or better still your compound.

Hi

I agree to this point …

So, to sum it up, when it comes to Sub2-micron particles…as you stated there is a problem with particle size analysis…and also if my knowledge is right, there is trouble in controlling a narrow particle size distribution…so Sub 2-micron particle size columns are grey are right??...wonder of all the Brands claiming of having “bestâ€

The issued with the particle size definition is not limited to sub-2-micron particles. It is a fundamental problem with all HPLC particles. Since even researchers who publish on this do not yet understand the subject, we need to live with the practical conventions.

If you want to understand particle size distributions at least to some degree, please read Chapter 4, "Physical Properties of HPLC Packings" in my book on "HPLC Columns".

I do not agree with the statement that there is a general problem with the analysis of sub-2-micron particles. The manufacturer must have the right tools to measure the particle size distribution, and understand what the tool measures.

To make sub-2-micron particles with a narrow distribution is also not a simple task, and not every manufacturer has tools of the same quality. The result has indeed been that some particle size distributions were very broad. On the other hand, you can rest assured that Waters, who started the game of UPLC and sub-2-micron particles, had the technology well in hand when UPLC was introduced several years ago.

Hi

Recently I was came across varian columns with 3 different particle size :- 3um, 2.8um and 2.4um..i was just wondering what is the advantage of such sample variation in particle size e.g the difference between 3um and 2.8um is just 0.2um..what added advantage could this bring in???

Minimal increase in efficiency, and very large increase in pressure