Dr. J. Kirkland during the award talk

Yesterday, I had a great opportunity to participate in Discussion group organized by the An International Separation Science Society (CASSS). The main topic was the Scientific Achievements Award for one of the founders of modern HPLC – Dr. Jack Kirkland.

Jack Kirkland is the inventor of superficially porous particle stationary phases. These particles have solid core covered with small layer of porous nanoparticles. Maybe you know them as Poroshell or Halo columns. Columns packed with these particles show extremely strong separation power for different kinds of applications. In the past, I had a opportunity to compare various types of chromatographic stationary phases (including totally porous, non-porous, superficially porous particles and monolithic stationary phases) and I have to confirm their strengths.

In his very inspiriting presentation Dr. Kirkland mentioned not only history of development but also current state of the art and possible future steps for superficially porous particles as stationary phases. Do you know, that the size of the Halo particles (2.7 μm) is chosen according the theory calculations (the highest achievable efficiency for certain conditions) as well as because of the end frits in the column (the holes in the frits are 2 μm wide so the particles with 2.7 μm i.d. can’t go through them therefore same frits as for 5 μm i.d. particles can be used)?

One of the most important message in the presentation was that in chromatography the separation is always a compromise. Either you are looking for high throughput (then your choice will be probably UPLC or monoliths) or you are looking for the best selectivity and peak capacity (and you are going to choose porous particles). I know, this paragraph is very schematic conclusion, however it is usually like this. You have to always choose what you want and what is your goal in separation and to separate.

I was also happy to meet another founder of the (high performance) liquid chromatography: Dr. Lloyd R. Snyder.

Superficially porous particles with thicker outer shells were used extensively for liquid-liquid chromatography [1] and as the support for early bonded-phase packings in reverse phase HPLC [2].

Structure of particles

Nowadays superficially porous particles typically have a 5-µm solid core and a ~ 0.25 – 1 µm thick outer shell with 30-nm pores. But, the thinner the shell, the smaller is the particle surface area and the less is the sample loadability of these particles. Therefore, there must be a compromise between the thickness of the sh

Scheme of superficially porous particle

ell to obtain good separation efficiency and good sample loadability. Thin porous shells lead to low surface areas, low retentivity, and low sample loadability; thicker shells of higher surface area produce higher retentivity and higher sample loadability.

Advantages

Superficial porous particles have unique characteristics that favour certain applications. Because of their size, macromolecules have very poor diffusional qualities. Therefore, the advantage is significant for the very short diffusional path lengths within the porous shell on the surface of superficial porous particles. Compared to conventional totally porous particles of the same size, superficial porous particles show improved mass-transfer kinetic properties that permit more rapid separations of macromolecules [3].

References

1. J. J. Kirkland, Anal. Chem., 41 (1969) 218.
2. J. J. Kirkland, J. J. DeStefano, J. Chromatogr. Sci., 8 (1970) 309.
3. J. J. Kirkland, Anal. Chem., 64 (1992) 1239.