| Abstract: | Stable silica gel sorbents with aliphatic or aromatic groups are formed by chemical modifications of the silanol groups with special reactive silanes. Various lipophilic surface modifications on silica gels with varying pore structures are tested with regard to their chemical and physico-chemical characteristics, their wettability and their chromatographic retention data. The main problem in TLC is the preparation of abrasion-resistant layers on glass or on foils which meet the usual high standard of quality and are also suited for quantitative determinations. Thin-layer chromatography on reversed-phase layers can only be performed if the complete wettability of the lipophilic stationary phase in dry form is guaranteed by the mobile phase. Adsorption-chromatographic separations with lipophilic eluents and reversed-phase partition-chromatographic separations with hydrophilic eluents are performed, for example, with dyes, with polycyclic aromatic hydrocarbons and with lipids. The great differences in selectivity caused by the various modifications of the sorbent and the varying eluent composition are remarkable. Ready-for-use layers with lipophilic surface modifications complement the existing range of pre-coated layers and thus widen the application of TLC and HPTLC considerably. |
