(753a) Liquid Chromatography at the Single-Molecule Level

Liquid
chromatography is an indispensable technique in the pharmaceutical industry
both for purification and validation of products.  The macroscopic movement and
development of chromatographic peaks in a column can be described at the
molecular level using the stochastic theory of chromatography.  Using this
conceptual link, we compared single-molecule dynamics of fatty acid molecules
at hydrophobic interfaces to macroscopic results obtained with a typical
analytical chromatography system.  We observed that molecules remained bound
over a broad distribution of times.  We made super-resolution spatial maps of molecule
adsorption and concluded that the heterogeneous kinetics were not due to
large-scale surface defects.

In the
single-molecule experiments, we varied the mobile phase composition and found large
changes in adsorption rate constants, whereas desorption rate constants were
relatively insensitive to the overlying mobile phase.  This finding emphasizes
the importance of stationary phase chemistry in determining column efficiency. Our
work demonstrates the unique potential of single-molecule measurements for connecting
molecular dynamics to macroscopic chromatographic phenomena.