Kromasil technical evidence

• Introduction
• Mechanical stability
• Chemical stability
• Surface properties
• Loadability
• Scalability

Why Kromasil offers superior loadability

For preparative and process scale chromatography, loadability is probably the most important property besides selectivity.

“In Kromasil we have succeeded in combining high loadability with high mechanical strength”

Loadability is determined by the following parameters:

• surface area
• pore size
• pore size distribution

and in some cases (e.g. chiral purifications):

• ligand density

When these parameters are optimized, high available surface area per unit column volume is obtained.

Specific surface area is a function of pore size and pore volume, as can be seen in figure 1. High pore volume results in high specific surface area, but also generally a weaker silica matrix due to less silica in the structure.

Fig. 1 - Important parameters influencing the available surface area of silica materials and the relationship between them if assuming cylindrical pores.

In Kromasil we have succeeded in combining high loadability with high mechanical strength.

What makes Kromasil unique is a combination of high pore volume and surface area, together with a very high mechanical strength.

Pore size and distribution

“The smaller the pores, the higher the surface area
(at constant pore volume)”

When maximizing loadability, the size of the molecule to be purified has to be considered because it determines the minimum pore diameter of the silica packing which can be utilized.

Kromasil packings are available in different pore sizes to optimally fit different applications. The upper limit in molecular weight for different pore sizes is illustrated in figure 2.

Fig. 2 - Available surface area of Kromasil 60 Å and 100 Å compared with other commercial materials of 60 Å pores, measured with polymer standards.

The separation of two diastereomers (mw approx. 700 g/mol) on Kromasil 60 Å bare silica and another commercial 30 Å bare silica is shown in figure 3 to illustrate the importance of available surface area.

Fig. 3 - Analytical and overload chromatograms showing the purification of a diastereomer on Kromasil 60 Å with high available surface area and a comparison with another commercial material, 30 Å, with low available surface area.

To show the impact of ligand density on capacity, a chiral separation using two experimental lots of Kromasil Chiral with different ligand densities is shown in the chromatograms in figure 4.

Fig. 4 - Separation of a racemate on experimental lots of Kromasil Chiral with different ligand densities.