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1 Acta Chromatographica

1 2001

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Investigation of adsorption isotherms for selected alcohols on chemically bonded stationary phases

Kaczmarski K., Sajewicz M., Nędza J., Kowalska T.

Acta Chromatographica

2001

No. 11

12-24

This study, similar to one already performed by Guiochon et al., has focused on tracing adsorbent heterogeneity and lateral interactions of the type adsorbate-adsorbate with the aid of suitable isotherm models. In our approach we made use of the classical Langmuir isotherm (which reflects neither adsorbent heterogeneity, nor lateral interactions among the analyte molecules), the Fowler-Guggenheim/Langmuir-Freundlich (FG/LF) and Fowler-Guggenheim/Jovanović-Freundlich (FG/JF) isotherms (each of which takes into the account both adsorbent heterogeneity and lateral adsorbate-adsorbate interactions); and the Jaroniec isotherm (which takes into account adsorbent heterogeneity only). In our study we investigated the column packing LiChrospher 100 RP-18 with 2-phenylethanol and 3-phenylpropanol as test solutes. It was established that for both test solutes all four isotherm models performed satisfactorily, although the Langmuir isotherm performed the worst and the Jaroniec isotherm the best. It was also established that the heterogeneity of this RP-18 packing is fairly insignificant and the packing can, therefore, be regarded as quasi-homogenous. This finding is not in accord with results obtained by Guiochon et al., who reported that the column packing Vydac RP-18 was highly heterogeneous. Evident differences between the quality of the chemically bonded adsorbent surfaces in these two RP-18 packings probably results from different anchorage of the octadecyl ligands to the silica matrix surface; this molecular-level difference was thoroughly explained in our study.