Analytical separations using molecular micelles in open-tubular capillary electrochromatography

Area of Science:

• Analytical Chemistry
• Separation Science
• Chromatography

Background:

• Conventional capillary electrochromatography (CEC) faces challenges with frits and silica particles.
• Open-tubular capillary electrochromatography (OT-CEC) offers an alternative by eliminating these issues.
• Polymeric surfactants, or molecular micelles, present a novel approach for OT-CEC stationary phases.

Purpose of the Study:

• To investigate the utility of a molecular micelle as a polymeric surfactant in open-tubular capillary electrochromatography (OT-CEC).
• To develop and evaluate a polyelectrolyte multilayer (PEM) coating procedure for fused-silica capillaries using a molecular micelle.
• To assess the separation performance and stability of the modified capillaries for hydrophobic analytes.

Main Methods:

• Fused-silica capillaries were coated using a polyelectrolyte multilayer (PEM) procedure with alternating layers of poly(diallyldimethylammonium chloride) and poly(sodium N-undecanoyl-L-glycinate) (a molecular micelle).
• The performance of the PEM-coated capillaries was evaluated using seven benzodiazepines as model hydrophobic analytes.
• Reproducibility (run-to-run, day-to-day, week-to-week, capillary-to-capillary) and stability (number of runs, pH tolerance) of the electroosmotic flow and separation were assessed.

Main Results:

• The PEM-coated capillaries demonstrated excellent run-to-run, day-to-day, week-to-week, and capillary-to-capillary reproducibility for electroosmotic flow (RSD < 1%).
• The modified capillary exhibited remarkable robustness, withstanding over 200 separation runs.
• The coating showed strong stability against extreme pH values, indicating broad applicability.
• Chromatographic performance was evaluated and compared to the monomeric form of the molecular micelle.

Conclusions:

• The developed polyelectrolyte multilayer coating using a molecular micelle is a highly effective and robust stationary phase for open-tubular capillary electrochromatography.
• This approach offers significant advantages for the separation of hydrophobic analytes due to its excellent reproducibility and stability.
• The method holds general utility for advanced chromatographic separations, particularly in analyzing challenging hydrophobic compounds.