A comprehensive study on capillary surface modifications for electrophoretic separations of liposomes

Electroosmotic flow significantly impacts the resolution of separations in capillary electrophoresis and its modification is often necessary. Coating of the inner capillary surface either dynamically or permanently offers a way to alter the electroosmotic flow, potentially reducing the adsorption of analytes, in our case liposomes, to the capillary wall. At first, we measured fluorescently labeled liposomes in an uncoated capillary by capillary electrophoresis with laser-induced fluorescence detection. We used a special procedure of the electrophoretic experiment allowing us to observe the development of peak shape at the early stages of migration. We proved that the liposomes were adsorbed to the capillary wall, which led to a very quick and severe dispersion of their peak during their electromigration. For this reason, we used a commercially coated capillary with polyvinyl alcohol, where at the same separation conditions, we observed the peak of the liposome with a stable shape during the migration. However, this capillary is costly, thus four simple dynamic coating methods were tested for four polymers, namely Pluronic F-127, polyvinyl pyrrolidone K30, polyethylene glycol, and polydiallyldimethylammonium chloride. Among them, we chose a method where we flushed the capillary with a 10% solution of polyvinyl pyrrolidone K30 before the first measurement. In addition, in-house made permanent coating with linear polyacrylamide was investigated, which has led to effective suppression of the electroosmotic flow and stable liposome peak, not dispersed during its migration. Liposome separation using this coating fully confirmed that the studied liposomes are negatively charged and migrate in the anodic direction.

Graphical abstract