Imaging solute distribution in capillary electrochromatography with laser scanning confocal microscopy

Area of Science:

• Analytical Chemistry
• Chromatography

Background:

• Direct visualization of solute-molecule interactions with stationary phases is crucial for understanding chromatographic separation mechanisms.
• Conventional imaging techniques struggle to resolve the detailed structure of stationary phases and solute distribution within packed columns.

Purpose of the Study:

• To develop and validate a direct imaging method for observing solute-stationary phase interactions under capillary electrochromatography (CEC) conditions.
• To investigate the utility of laser scanning confocal fluorescence microscopy for analyzing solute distribution and stationary phase morphology.

Main Methods:

• Utilized laser scanning confocal fluorescence microscopy to image solute distribution within a C18 packed capillary under CEC conditions.
• Employed optical sectioning capabilities of confocal microscopy to distinguish between stationary phase beads and the mobile phase.
• Analyzed intensity distributions over time and at different depths to probe internal bead structure and molecular partitioning.

Main Results:

• Confocal imaging clearly delineated C18 silica beads and the surrounding mobile phase, overcoming limitations of conventional methods.
• Fluorescein molecules showed preference for the mobile phase, while Nile Red and rhodamine 6G localized within the C18 beads.
• Identified a small fraction (2%) of silica beads with porous shells and nonporous cores, revealing heterogeneity in stationary phase structure.

Conclusions:

• Direct imaging of solute-stationary phase interactions is feasible and provides valuable mechanistic insights.
• The method allows for detailed characterization of stationary phase quality and column packing structure.
• This technique holds potential for advancing the understanding of separation mechanisms in both CEC and reversed-phase liquid chromatography.