The diffusional mobilities of potassium ferricyanide (Fe(CN)(6)(3-)) and ferrocene methanol (FcCH(2)OH) encapsulated within silica monoliths have been investigated using cyclic voltammetry and chronoamperometry at an ultramicroelectrode. In this work, a 13-mu m-radius Pt microdisk working electrode and a silver chloride coated silver wire (r = 0.5 mm) reference electrode were inserted into doped silica sols prepared by the sol-gel process. The resultant gels were aged and slowly dried under a relative humidity atmosphere of 60-70% to minimize gel cracking. Fast-scan voltammetry (up to 100 V/s) confirmed that the gel-electrode interface remained intact throughout the duration of the drying period (typically 20-50 days). During this time frame, an ca. 30% loss in mass and ca. 50% reduction in volume of the gels were observed. The diffusion coefficients of gel-encapsulated Fe(CN)(6)(3-) and FcCH(2)OH were measured without prior knowledge of dopant concentration via normalization of the chronoamperometric response with the steady-state limiting current obtained from a 2 mV/s potential sweep. For gel-encapsulated FcCH(2)OH, the diffusion coefficient dropped from ca. 4 x 10(-6) cm(2)/s to less than 0.6 x 10(-6) cm(2)/s as the gel dried, whereas for gel-encapsulated Fe(CN)(6)(3-), a near constant value of 2 x 10(-6) cm(2)/s was obtained. These results suggest that transport in these solids is influenced by both gel structure and by the nature of the entrapped reagent.