Silylation, of glassware

Silylation of apparatus makes it repellant to water and hydrophilic materials. It minimises loss of solute by adsorption onto the walls of the container. The glassware is placed in a desiccator containing dichloromethyl silane (ImL) in a small beaker and evacuated for 5min. The vacuum is turned off and air is introduced into the desiccator which allows the silylating agent to coat the glassware uniformly. The desiccator is then evacuated, closed and set aside for 2h. The glassware is removed from the desiccator and baked at 180° for 2h before use. 

The silylation of all glassware that contacts the plant extract has proven to effectively reduce adsorption losses. As diagrammed in Figure 8, the hydroxyl adsorption sites on the silica surface can be coated with dichlordimethyl silane. The unreacted chloride groups are then displaced with methanol in a substitution reaction. A secondary advantage of the silyation process is that water will not adhere to the glass surface. Aqueous residues bead together, which allows more efficient sample transfers. 

Fenimore, D.C., C.M. Davis, J.H. Whitford, and C.A. Harrington. 1976. Vapor phase silylation of laboratory glassware. Anal. Chem. 48 2289-2290. 

Surface silylation of solid supports, glass columns, inserts, or even glass-wool spacers and glassware for the sake of surface deactivation remains highly recommended in biochemical GC. An alternative approach to surface deactivation is the method of Aue et al. [93], in which thermal treatment of polymer-coated supports results in a partial linkage of the macromolecule to the surface. This approach has been successfully employed with both packed and capillary columns. 

Silylating agents have also been used to treat glassware before handling moisture-sensitive compounds. For example, a chlorine-terminated polydimethyl si-loxane is available commercially.3 These reagents suppress the basicity of the glass and provide a hydrophobic surface. 

Early in our work we frequently obtained erratic analytical results which were subsequently traced to cross-contamination between samples. In order to eliminate this source of error we instituted use of disposable pipettes and adopted a far more rigorous cleaning procedure for that glassware which is reused. All of our glassware is also silylated by the vapor-phase procedure recently reported by Fenimore, et. al. (5). 

However, the success of the rearrangement of 10 is dependent on the purity of the starting material. Trace impurities increase the amount of elimination products. Careful chromatography, the use of silylated glassware [5% bis(trimethylsilyl)acetamide/pentane, reflux, 10 h] as well as conducting the reaction under dilution conditions, are also necessary for success567. 

Hence, the sensitivity requirements for the determination of A -THC are indicated in Fig. 4. Plasma levels will obviously be modified by the amount of THC absorbed and by the rate of absorption but if levels are to be measured later than 4 hours after administration a sensitivity of 1 ng/ml is required. Such as sensitivity combined with specificity is perhaps limited to the mass fragmentographic techniques. We have so far encountered little interference in the mass fragmento graphic determination of A -THC provided redistilled solvents, particularly ethanol, and all silanized glassware are used. If interference does occur the silylation technique provides an alternative. 

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