Performance and preparation of immobilized polysiloxane stationary phases in 5–55 μm I.D. open-tubular fused silica columns for liquid chromatography

Abstract

Cross-linked non-polar polysiloxanes were evaluated as stationary phases in open-tubular column reversed-phase liquid chromatography. Coating of 5–55 μm I.D. fused-silica capillaries with stationary phase films of a well defined thickness in the range 0.03–1.96 μm is described for the two polysiloxane gum phases PS-255 (methylvinyl silicone) and SE-54 (methylphenylvinyl silicone). The chromatographic properties of these columns were investigated using split injection and on-column laser-induced fluorescence detection. Gas chromatography was used complementarily in the evaluation of column stability, retention and inertness. A retentive layer thickness to column diameter ratio up to 1:27 could be prepared. A retentive layer thickness to column diameter ratio up to 1:27 could be prepared, and a linear relationship was observed between the retention and the stationary to mobile phase volume ratio. The selectivity was related to the polysiloxane structure and was constant for films thicker than 0.25 μm. The column band-broadening was studied regarding the contribution from stationary phase diffusion, and compared with theory. Depending on film thickness, the stationary phase diffusion coefficient D s was in the range 10 −8-10 −6 cm 2/s. The highest efficiency, 351 000 plates ( k′ = 0.16), was obtained with a 1.97 m × 11.7 μm I.D. open-tubular-column. An application to the gradient separation of fluorescence labelled amino acids is presented. Preliminary results are also reported on a new type of stationary phase, created by swelling the immobilized polysiloxane with n-heptane. A nearly ten-fold increase in retention and a change in selectivity were obtained.