A kinetic parameter concerning mass transfer in silica monolithic and particulate stationary phases measured by the peak-parking and slow-elution methods
✍ Scribed by Kanji Miyabe; Hiroshi Kobayashi; Daisuke Tokuda; Nobuo Tanaka
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 810 KB
- Volume
- 29
- Category
- Article
- ISSN
- 1615-9306
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✦ Synopsis
Abstract
Mass transfer in monolithic C~18~‐silica stationary phases and C~18~‐silica gel particles was studied. A traditional kinetic parameter, γ~s~D~s~, which is a diffusion coefficient of solute molecules in the stationary phase, was measured by two unusual approaches, i. e., peak‐parking and slow‐elution methods. The correlation between the ratio of γ~s~D~s~ to molecular diffusivity (D~m~) and the retention factor (k) was represented by one common curve, irrespective of the RPLC conditions. A similar curved profile was also observed between another kinetic parameter (D~Ls~), which is related to the axial diffusive molecular migration in the stationary phase, and the retention equilibrium constant (K~a~). The values of D~Ls~ and K~a~ were calculated from those of γ~s~D~s~ and k, respectively. The ratio of D~Ls~/D~m~ increases with decreasing K~a~ and seems to approach around unity when K~a~ is infinitely small. The dependence of D~Ls~ on K~a~ was also studied from extra‐thermodynamic points of view. The linear correlation between ln D~Ls~ and ln K~a~ suggests the existence of a kind of linear free energy relationship between the mass transfer in the stationary phase and the retention equilibrium. Because these characteristics of D~Ls~ are similar to those of the surface diffusion coefficient (D~sur~), D~Ls~ seems to correspond to D~sur~.