In-line valve injection for capillary electrophoresis

Area of Science:

• Analytical Chemistry
• Separation Science

Background:

• Capillary electrophoresis (CE) is a powerful separation technique.
• Traditional injection methods can limit CE performance.
• Integrating injection systems directly into CE is desirable for advanced applications.

Purpose of the Study:

• To demonstrate the feasibility of direct in-line injection for capillary electrophoresis using a commercial liquid chromatography valve.
• To evaluate the reproducibility and separation performance of this injection method.
• To assess the suitability of valve materials for high-voltage CE applications.

Main Methods:

• Utilized a commercially available liquid chromatography injection valve with ceramic and PEEK internal components.
• Performed direct in-line injections for capillary electrophoresis experiments up to 20 kV.
• Quantified injection reproducibility and measured theoretical plates for various capillary inner diameters.

Main Results:

• Achieved highly reproducible partial-loop injections ranging from 6 to > 60 nL.
• Demonstrated that the valve's materials provide adequate dielectric insulation for high-voltage operation.
• Observed excellent separation performance with theoretical plates up to 2.5 x 10^5 for 100-microm-i.d. capillaries.
• Reported small and symmetrical extracolumn variance from the valve injection system.

Conclusions:

• Direct in-line valve injection is a viable and effective method for capillary electrophoresis.
• This technique offers high reproducibility and excellent separation efficiency, comparable to direct electrokinetic injections.
• The successful integration of LC injection valves into CE instrumentation has significant implications for developing advanced, integrated analytical systems.