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Molecular interactions at octadecylated chromatographic surfaces.
J W Burns1, S E Bialkowski, D B Marshall
1Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300.
Analytical Chemistry
|June 7, 2011
Summary
This study used fluorescence to map fluorescent probes within octadecylated silica surfaces, revealing how solute interactions and mobile phase changes affect probe location in reversed-phase high-performance liquid chromatography.
Area of Science:
- Analytical Chemistry
- Chromatography
- Surface Science
Background:
- Understanding solute interactions with stationary phases is crucial for optimizing reversed-phase high-performance liquid chromatography (RP-HPLC).
- Octadecylated silica is a widely used stationary phase, but its interfacial properties and probe behavior are complex.
- Fluorescence techniques offer sensitive methods for probing molecular environments at interfaces.
Purpose of the Study:
- To investigate the interactions of fluorescent solutes with an octadecylated silica surface.
- To determine the location and environment of fluorescent probes within the bonded phase layer under varying mobile phase conditions.
- To interpret these findings in the context of RP-HPLC separation mechanisms.
Main Methods:
- Utilized fluorescence emission spectra and quenching techniques with various fluorescent probes (pyrene, benzo[a]pyrene, fluorene, biphenyl, propyldansylamide, decyldansylamide) and quenchers (potassium iodide, N,N-dimethylaniline).
- Employed aqueous methanol mobile phases with methanol concentrations ranging from 60% to 100%.
- Analyzed solvent-dependent spectral shifts, vibronic band intensities, and quencher accessibility to infer probe location and environment.
Main Results:
- Biphenyl and pyrene probes were found in nonpolar environments deep within the bonded phase layer.
- Propyldansylamide and decyldansylamide probes exhibited environments that became more polar with increasing water content.
- Benzo[a]pyrene showed increased exposure to the mobile phase with higher water content, possibly due to solute size and chain collapse.
- Fluorene demonstrated strong interactions with silanol groups.
Conclusions:
- The chain cluster model provides a better explanation for the observed probe behaviors than the surface convolution model.
- Probe location and interfacial environment are significantly influenced by mobile phase composition and solute properties.
- These findings have direct implications for understanding and improving solute separation in RP-HPLC.
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