Improvement of the long-term stability of polyimide-coated fused-silica capillaries used in capillary electrophoresis and capillary electrochromatography

Swelling of the polyimide coating of fused-silica capillaries in acetonitrile-containing buffers was found to be the reason for several problems in capillary electrophoresis (CE) and capillary electrochromatography (CEC). Scanning electron microscopy photographs of the ends of raw fused-silica tubing showed that the coating becomes soft and increases its volume after longer contact with such buffers. As a consequence, separation efficiency can deteriorate, the capillary ends can clog or break off. To prevent swelling of the polyimide coating, fused-silica capillaries used in CE or CEC were heated at 300 °C for a longer period of time which improved their long-term stability in comparison to raw fused-silica tubing.