Non-particulate (continuous bed or monolithic) acrylate-based capillary columns for reversed-phase liquid...

Area of Science:

• Analytical Chemistry
• Separation Science
• Polymer Chemistry

Background:

• Reversed-phase capillary liquid chromatography and electrochromatography require specialized stationary phases.
• Non-particulate beds, or monoliths, offer advantages over traditional packed columns.
• Developing robust and efficient monolithic columns in aqueous media presents synthetic challenges.

Purpose of the Study:

• To synthesize and evaluate three distinct approaches for creating acrylic non-particulate beds in aqueous polymerization media.
• To assess the hydrophobicity, separation efficiency, and electroosmotic properties of the synthesized monolithic columns.
• To investigate the impact of polymerization temperature on column characteristics such as permeability and porosity.

Main Methods:

• Synthesis of acrylic non-particulate beds using hexyl acrylate with polar comonomers and a non-ionic detergent.
• Synthesis utilizing a novel water-soluble alkyl ammonium salt comonomer with inherent detergent properties.
• Employing the alkyl comonomer as a detergent to solubilize another hydrophobic comonomer in aqueous polymerization.
• Characterization through methylene group selectivity, electroosmotic mobility measurements, and plate count determination for methylparabene.
• Evaluation of column performance using pressure-driven capillary chromatography and capillary electrochromatography.
• Analysis of polymerization temperature effects on hydrodynamic permeability, separation impedance, and porosimetry.

Main Results:

• The three synthetic approaches yielded non-particulate beds with varying hydrophobicity (methylene selectivity 1.86, 1.16, 1.78), electroosmotic mobility (-5.14 x 10(-5), 6.89 x 10(-5), 6.37 x 10(-5) cm2 V(-1) s(-1)), and efficiency (67,000, 93,000, 110,000 plates m(-1)).
• The second approach, using the novel alkyl ammonium salt comonomer, demonstrated excellent electroosmotic properties and high efficiency.
• Increased polymerization temperature led to higher bed permeability and separation impedance, but decreased polymeric skeleton porosity.
• Separation efficiency was further confirmed using series of benzoic acid esters and alkyl parabens.

Conclusions:

• All three developed methods successfully produced acrylic non-particulate beds suitable for capillary chromatography and electrochromatography.
• The choice of comonomer and synthetic strategy significantly influences the hydrophobicity, electroosmotic flow, and separation efficiency of the monolithic columns.
• Polymerization temperature is a critical parameter affecting the physical and separation characteristics of the synthesized beds.