Deactivation and preparation of fused silica open tubular columns for gas and supercritical fluid chromatography

Abstract

The activity and wettability of raw fused silica capillary tubing was found to be widely variable which places severe limitations on the reproducibility of column deactivation and inertness. Hydrothermal treatment of the raw fused silica with nitric acid was proven to be very effective for cleaning and maximizing the degree of silanol coverage of the surface. The capillary rise method was used to obtain contact angle data for untreated fused silica and fused silica treated with a variety of deactivating reagents. This contact angle data was used in the construction of Zisman plots which allowed quantitative comparison of the wettability and degree of surface coverage obtained with the different deactivants. The thermal stability of the final column was related to the success of the deactivation procedure. The choice of cross-linking initiator was also found to have an affect on column inertness.

In the synthesis of intermediate polarity polysiloxane stationary phases, mixtures of commercially available cyclic siloxanes were shown to be a viable alternative to the use of dichlorosilanes as starting material. The main advantages were the simplification of the synthesis procedure, simpler and better molecular weight control of the polymer, and the elimination of HC1 as a by-product of both the polymerization and endcapping steps. A new stationary phase, 7% cyanoethyl, 7% phenyl, 1% vinyl, methyl polysiloxane was synthesized and found to be more polar than OV-1701 with higher temperature stability, easily cross-linked, and suitable for use in supercritical fluid chromatography.