Probes Based on Silica Sol-Gels for Voltammetry in the Absence of Electrolyte in the Sample Phase
This cell design was evaluated as an amperometric detector for gas chromatography. Initial experiments were in the flow injection mode with He flowed at 0.63 mL min-1 as the carrier gas and100- µL injections of H2 comprised the sample. Wirh a Pt working electrode at 0.5 V vs. a Pt quasi-reference electrode, linear response to concentration over range 1.7 x 10-6 g to 7.6 x 10-6 g was observed. Extensions to 1,2-ethandithiol, phenol, p-cresol, and thioanisole yielded detection limits of 4, 1, 3, and 70 ppmv (k = 3 criterion), respectively, when operating the working electrode at 800 mV. Application to aqueous samples in the absence of supporting electrolyte also were achieved; however, a problem is that leaching of the electrolyte from the sol-gel cell was a limitation. To address this problem, the sol-gel matrix is being modified to contain a macromolar cation (anion) of a size that is greater than the ca. 0.5 nm pore size of the silica. An example is to immobilize 3,4- ethyelenedioxythiophene (EDOT) in the sol-gel and oxidize it to the polymeric form, PEDOT. Results on the polymerization process will be shown, and the efficacy of the resulting composite as a matrix for a probe to determine various species in water in the absence of supporting electrolyte will be presented.