Silica capillaries have been an integral part of the instrumentation used in many areas of analytical chemistry for decades, especially in analytical separations. In most cases, they are used without treatment, occasionally forceless chemical surface treatments are made to suppress or enhance the activity of silanol groups.
The aim of this work was to disrupt the inner surface of the capillary, perfectly smooth from manufactory, so that relatively coarse and various structures would be created, and to study their influence on the separation efficiency. The uniqueness of the used solution is based on the use of special properties of water exposed to high temperatures and pressures (supercritical water), which is able to disrupt this chemically inert material because of its aggressivity. In total, over 2000 experiments were carried out in order to define conditions suitable for the formation of various types of surface structures. Due to the high amount of resulting data, our own database application was created, allowing not only to save the picture of the structure and experimental conditions information, but also to clearly sort them out and create image reports according to the specified parameters.
Samples representing individual types of structures were then selected from this database and a number of silica capillaries with a configuration suitable for electromigration analyzes were prepared. The creation of a structured surface in the input part of the separation capillary enabled the separation of some classes of substances and biosamples, which cannot be analyzed on standard capillaries with a smooth surface.
An example is the complete separation of two strains of Staphyllococcus aureus bacteria (MRSA and MSSA), or the use of the absorbing capabilities of a structured surface to study the interactions of these bacteria with bacteriophages. This ability was also used in the determination of Aspergillus fungus in a sample taken directly from the patient's lungs, where there was achieved a significant increase in the sensitivity of the analysis. Structured capillaries can also be used in the analysis of food samples, i.e., for the separation of β-lactoglobulins A and B in cow's milk, which belong to its main allergens.