ac9612584_si_001.pdf (257.62 kB)
Molecular Interactions at Octadecylated Chromatographic Surfaces
journal contribution
posted on 1997-10-01, 00:00 authored by James W. Burns, Stephen E. Bialkowski, David B. MarshallInteractions between fluorescent solutes and an octadecylated silica surface are investigated using fluorescence
emission spectra and quenching techniques under conditions similar to those found in high-performance liquid
chromatography. Pyrene, benzo[a]pyrene,
fluorene, biphenyl, propyldansylamide, and decyldansylamide are
used as the fluorescent probes, and potassium iodide and
N,N-dimethylaniline are used as quenchers.
N,N-Dimethylaniline is a moderately retained quencher thought
to probe deeper into the octadecylated surface than the
ionic iodide salt. Solvent-dependent fluorescence
emission maxima, solvent-dependent fluorescence vibronic
band intensities, and quencher access to the probes are
investigated using aqueous methanol mobile phase compositions ranging from 60 to 100% methanol. The
resulting information is used to interpret differences in interfacial probe environments and to determine the location
of the probes within the bonded phase layer. The data
indicate that biphenyl and pyrene may remain in very
nonpolar interfacial probe environments deep in the
bonded phase layer over the mobile phase composition
range tested. The fluorophore portion of both
propyldansylamide and decyldansylamide may reside in an interfacial environment, which becomes more polar as the
water content in the mobile phase is increased.
Benzo[a]pyrene apparently becomes exposed to the
mobile
phase as the water content in the mobile phase increases.
This is thought to be due to the relatively large size of
the
solute molecule and the collapse of the octadecyl chains
with increased solvent polarity. Fluorene appears to
interact strongly with silanol groups. The results
are
interpreted in light of the surface convolution and chain
cluster octadecylated chromatography surface models and
are found to be more constant with the chain cluster
model. Implications of the results to reversed phase
high-performance liquid chromatography separations are also
discussed.