The "Wall Effect" in Chromatography

[M_Farooq]

In the chromatographic literature it is mentioned that particles around the column walls are not very tight packed. On the other hand, some publications mention that the wall region is tightly packed than the bulk. It is easier to understand that the column walls are rigid and one cannot fit spheres perfectly but in which case the wall ares is more tightly packed than the bulk? The group which did a study showed that the solute travels slower along the wall area than the bulk. They never explained as to why a wall region become more tightly packed than the bulk?

Note that this is a fundamental reason why no peak is 100% symmetric (skew =0) in any HPLC column.

Regards,

Farooq

[Gerhard Kratz]

Good Morning Farooq,
These wall effects are important for particle sizes above 5µm. Many years ago I had a discussion with Uwe Neue about that. When it comes to smaller particles, 3µm, 2µm and sub 2µm this effect is still there but so small that it would make no sense to measure it. In process chromatography it is a very important effect and therefore many different packing techniques were developed.
Maybe next Pittcon or HPLC will be a poster or oral presentation on such issues, who knows.
Have an excellent day.

[M_Farooq]

Dear

Good Morning Farooq,
These wall effects are important for particle sizes above 5µm. Many years ago I had a discussion with Uwe Neue about that. When it comes to smaller particles, 3µm, 2µm and sub 2µm this effect is still there but so small that it would make no sense to measure it. In process chromatography it is a very important effect and therefore many different packing techniques were developed. Maybe next Pittcon or HPLC will be a poster or oral presentation on such issues, who knows. Have an excellent day.

Good morning, There is very recent study with sub 2 microm particles packed in capillaries. They showed (using microscopy) that there are significant variations in porosity near the walls and the bulk region is almost uniform. This wall effect continues till few particle diameters. Here is the article. Their figure shows that the wall area is more ordered (I may be wrong) and the bulk is random packed. I was trying to understand the porosity oscillations near the walls. This is Figure 5.

http://www.sciencedirect.com/science/ar ... 7313016178

I would be presenting something on the peak shapes in Pittcon.

[Consumer Products Guy]

This is the wall effect I experience most:

[Sallybeetle]

This is the wall effect I experience most:

Dear CPG:
You "hit the nail on the head." I need to paste these emoticons on my HPLC system, maybe ward of what ever is keeping it from doing at least one day's work.

[Consumer Products Guy]

Dear CPG:
You "hit the nail on the head." I need to paste these emoticons on my HPLC system, maybe ward of what ever is keeping it from doing at least one day's work.

So they're called "emoticons" ? See, I learn something every day. I borrowed them from an Internet Forum on old trucks.