Abstract High-temperature silylation (HTS) on leached glass capillaries is highly effective deactivation method for preparing neutral and inert surfaces. Several silylating agents such as disilazanes and disiloxanes containing different alkyl groups and phenyl groups were prepared and investigated for their usefulness in HTS. The conditions of the procedure, especially the influence of the amount of silylating agent, were examined. It was found that most of the reagents are suitable for use in HTS in achieving very low adsorption activities of the treated glass surface. With increasing chain-length or number of phenyl groups in the reagent, not only was a change of critical surface energy of the treated glass capillaries effected but also a better wettability for numerous stationary phases was observed.