gel porosity – Chromatographer

Crosslinking monomer: another way how to improve column efficiency

From my point of view, the preparation of polymer monolithic stationary phases suitable for the separation of small molecules is one of the hotter topics now in monolithic chromatography. There are several ways how to improve their separation power for small molecules. It is possible to increase their surface area either by hypercrosslinking modification or with the combination of non-polar and polar monomers. Another possibility is to prepare low-surface area (but efficient) materials by the termination of the polymerization reaction at the early stages or by application of crosslinking monomer with longer atom chain in between two methacrylate units.

We have extended the later approach and recently published the article describing the one-step preparation of highly efficient columns for the separation of small molecules.

Separation of small molecules: surface area vs. gel porosity

Generally, methacrylic acid is used as a charge-bearing agent for generation of electroosmotic flow in capillary electrochromatography. However, methacrylic acid has a significant effect on the morphology of the monolithic stationary phases based on styrene – divinylbenzene system as showed recently by group in Prague.

The monolithic material prepared without methacrylic acid in the polymerization mixture showed a very low surface area of 0.1 m²/g, whereas the surface area of organic polymer monolith with methacrylic acid increased significantly up to 261 m²/g. The addition of methacrylic acid in to the polymerization mixture improves also separation power of prepared monolithic columns. Figure 1 shows the separation of the mixture of small molecules on the column without (A) and with (B) methacrylic acid in the polymerization mixture.