Head-Column Field-Amplified Sample Stacking in Binary System Capillary Electrophoresis:  A Robust Approach Providing...

Area of Science:

• Analytical Chemistry
• Separation Science
• Capillary Electrophoresis

Background:

• Capillary electrophoresis (CE) offers high separation efficiency but often suffers from limited sensitivity for trace analysis.
• Existing sample preconcentration techniques can be complex or introduce artifacts.
• Field-amplified sample stacking (FASS) is a promising technique for enhancing CE sensitivity.

Purpose of the Study:

• To develop and validate an effective electrokinetic field-amplified sample injection (e-FASI) method for capillary electrophoresis.
• To achieve significant sensitivity enhancement for analyzing positively chargeable, hydrophobic compounds.
• To optimize injection parameters to prevent thermal degradation and ensure reproducibility.

Main Methods:

• Head-column field-amplified sample stacking (HCFASS) was employed, introducing a low-conductivity water plug at the capillary inlet.
• Optimized injection voltage (<20 kV) and time (<60 s) were used to prevent solvent boiling and solute deposition.
• Analysis of positively chargeable model compounds (amiodarone, desethylamiodarone) was performed using UV absorption detection.

Main Results:

• Over 1000-fold sensitivity enhancement was achieved for sample volumes up to 10-fold the capillary volume.
• Reproducible results were obtained over 1500 runs by controlling injection parameters and preventing heat damage.
• Optimal conditions included a >1 mm water plug, low conductivity, high organic solvent content, and 50-100 μM H+.
• Nanomolar level solutes were detected from ~4 μL sample volume.
• Internal calibration based on peak height provided reliable quantitation (RSDs ~2%).

Conclusions:

• Head-column field-amplified sample stacking is a robust and highly sensitive technique for CE analysis of hydrophobic compounds.
• Careful control of injection parameters is crucial for preventing thermal issues and ensuring reliable quantitation.
• The method enables sensitive detection of trace analytes, expanding the applicability of capillary electrophoresis.