First Silanol-Free High pH Silica-Based C18 Column

February 1, 2018
Imtakt USA
The Application Notebook

Volume 36, Issue 2

Page Number: 15

A fundamental challenge in reversed phase chromatography has been the presence of surface silanols on silica-based particles, despite various methods of end-capping. Here, we introduce Dacapo DX-C18 with Dual-Matrix technology, a polymer/silica particle with no exposed silanols, and excellent stability from low to high pH ranges.

Traditionally, silica-based particle columns have been used in reversed phase chromatography because they have a much higher mechanical stability compared to polymer based particle columns. However, unlike polymer-based columns, they are prone to degradation at high pH due to attack by excess hydroxide ions at the silica surface.

Various attempts to bridge this gap have been made such as surface polymer integration into the silica structure or polymeric end-capping, but due to the need for exposed surface silanol for silylation attachment of the C18 ligand, there have always been remaining exposed surface silanols. These left over silanols can adversely affect peak shape, particularly for basic compounds, where ionic interaction between positively charged analytes and negatively charged surface silanols can lead to poor peak shape. These surface silanols also represent weak points in the silica structure where high pH mobile phases can dissolve the particle, leading to reduced column life.

Dacapo DX-C18 is the first "Dual-Matrix" structure in the world (Figure 1). It combines the mechanical strength of porous silica with the wide pH stability of polymer-based columns. This Imtakt exclusive design brings the best of both types of columns into one, with a porous silica matrix providing the ability to withstand high pressures and a wide range of organic solvents, and the organic polymer matrix providing resistance to degradation under high pH conditions. This design also eliminates exposure of surface silanols improving peak shape for basic compounds.


Figure 1: Dacapo DX-C18 Dual-Matrix technology.

Experimental Conditions

Figure 2 compares Dacapo DX-C18, with a high pH hybrid-silica ODS column. The analytes were basic drug compounds (tricyclic antidepressants). Both columns were tested with the same dimensions (50 × 4.6 mm, 2.5 µm) and running conditions (see Figure 2).


Figure 2: Silanol-free Dacapo DX-C18 shows better peak shape for basic compounds versus a hybrid-silica column (grey).

Result and Discussion

The basic compounds tested behaved very differently, despite the columns having the same stationary phase (C18), the same particle size (2.5 µm), and dimensions (50 × 4.6 mm). Dacapo DX-C18 produced symmetrical, narrow peaks, where the hybrid-silica column delivered peaks with shoulders, splitting, high asymmetry, and overall poor resolution. These differences are likely due to secondary interaction with exposed surface silanols, which are not seen in the silanol-free Dacapo DX-C18 column. Dacapo DX-C18 also shows better resolution and higher sensitivity at less than half the run time of the other columns.

Conclusion

Dacapo DX-C18 Dual-Matrix technology provides the best of both silica and polymer-based particle design. This Imtakt exclusive design completely eliminates surface silanols, improving peak shape for basic compounds. This surface treatment also extends column life under alkali conditions, making this ground-breaking new technology an exciting choice for a reversed phase column that delivers outstanding results.

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