Simple functionalized quaternary ammonium salts as stable silicawall modifiers for CE-MS analysis of biological molecules

Capillary electrophoresis is today a well consolidated analytical technique, applied to almost all research fields where molecules’ separation is crucial. This technique has been quickly developed in all its structural components like the detectors, the electrophoretic modes and the automation. But there is still a weak point just at the core of the technique: the fused silica capillary. Our group has been committed since several years to synthesize silica wall modifiers characterized by the following properties: to be simple molecules cheap to produce, chemically stable, easy and fast to use also by unskilled operators, reliable and, even more importantly, compatible with MS detectors without the risk of leakage or instrument fouling. Here we present the main properties, as silica wall modifiers and EOF modulators, of some compounds that we have synthesized and tested on the analysis of proteins and molecules of biological origin. These modifiers are, basically, functionalized quaternary ammonium salts: some of them, although being small and simple molecules, show the peculiar property of eliciting a very quick and very stable association with the silica surface, comparable with that of covalently bonded silica coatings. Due to their high stability and low molecular mass, potential release phenomena are minimized, so that these coatings do not interfere with mass detections and are not dangerous to mass spectrometry instrumentation.