G.A.F.M. Rutten

Determination of solute diffusion coefficients in cross-linked stationary phases for fused-silica columns

Precise measurements of plate heights of fused-silica columns with either cross-linked or conventionally coated stationary liquids were used to determine solute diffusion coefficients in these media. Three different methods of calculating liquid diffusion coefficients from chromatographic data were evaluated. The most accurate results were obtained by combination of plate heights for two different carrier gases. Contrary to expectation, no significant differences were found between diffusion coefficients in conventional or in situ cross-linked stationary liquids. Solute diffusion coefficients are listed for n-alkanes in CP-Sil-5, OV-1, CP-Sil-5-CB and OV-1-CB.

Deactivation with polymethylhydrosiloxane : a comparative study with capillary gas chromatography and solid-state 29Si nuclear magnetic resonance spectroscopy

Deactivation of fused-silica capillary columns and vitreous silica surfaces with polymethylhydrosiloxanes (PMHS) at temperatures between 240 and 360°C was investigated by gas chromatography (GC) and solid-state 29Si NMR spectroscopy. The influence of temperature, amount of water at the surface and film thickness on the stability and nature of the polymer deactivation layer was studied by solid-state 29Si NMR of the model substrate Cab-O-Sil, a fumed silica. These NMR measurements match the GC results and offer additional information relating to the nature of the deactivating layer at surfaces silylated under various reaction conditions. Differences in the nature and structure of the deactivating film occur when the silica surface is coated with a different thickness. Optimum deactivation is achieved when a few monolayers of densely cross-linked polymers anchored to the silica surface are formed. On top of this thin, rigid layer, longer mobile polymer chains containing unreacted silicon hydride groups are present. After optimum deactivation, the fused-silica capillary column wall shows no interaction with various critical test components as used in GC practice. The deactivating films exhibit good thermal stability and solvent resistance.