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Temperature-Jump Investigation of Sorption/Desorption Kinetics at Reversed-Phase Chromatographic Silica/Solution Interfaces

Year: 1994
Type: article
Abstract: Most of our understanding of chromatographic processes has been inferred from retention measurements. These measurements do not generally provide information about the role of sorption and desorption kinetics on retention equilibria. In this work, we show that temperature-jump relaxation techniques can be used to monitor reversible kinetics at the liquid/solid interface. A Joule-discharge apparatus is used to heat a packed bed of porous silica gel on a microsecond time scale. We have observed sorption/desorption relaxation kinetics for a fluorescent probe, 1-anilino-8-naphthalene sulfonate (ANS) at a C18-modified silica surface. On a 100 μs time scale, a slow relaxation was detected having a rate that increased as retention of the solute was increased by changes in mobile phase composition. This behavior suggested that sorption kinetics were controlling the relaxation rate; the linear dependence of the rate on the concentration of the probe in the mobile phase verified this postulate. The results showed further that the adsorption rate of this ionic probe is slower than diffusion-limited and exhibits significant influence over the equilibrium constant. Here, the sorption rates of two neutral probes, however, were indistinguishable from a diffusion limit indicating a negligible barrier to sorption. While sorption kinetics are generally too fast to play a significant role in band broadening, these results show that their influence on the equilibrium constant in the case of ionic solutes cannot be overlooked, and that similar retention equilibria can arise from vastly different underlying kinetic mechanisms.
DOI: 10.1021/ac00085a021
Institution: University of Utah
Language: English
Subfield: Spectroscopy
Field: Chemistry
Open Access status: green
OpenAlex ID: W2038247199
FWCI: 2.119
Cites: 40
Cited by: 23
Related to: 10