A device that combines a working and counter electrode connected to each other via a poly(ethylene oxide) film containing electrolyte forms a self-contained electrochemical cell that has been-used to inspect the voltammetry of p-benzoquinone and anthracene in CO2-based fluids. Interest in the voltammetry of these compounds in CO2-based fluids is derived from their potential amenability to electrochemical detection coupled to supercritical fluid separations. With appropriate formulation of the poly(ethylene oxide) films, both compounds may be voltammetrically detected in CO2 with or without the use of polar fluid modifiers. The compatibility of voltammetry with modified and unmodified fluids, as demonstrated herein,is a feature lacking from most presently available detectors used in supercritical fluid chromatography. Furthermore, following electroreduction, both compounds are susceptible to electrophilic addition by CO2 to yield carboxylated compounds. This provides an opportunity to investigate CO2-based fluids as a reagent as well as a medium for electrochemistry. Evidence is obtained that the rate of the carboxylation reaction which follows reduction of each compound is enhanced in CO2-based fluids compared to the rate of carboxylation in CO2-saturated acetonitrile. The enhanced rate observed in CO2-based fluids is attributed to the greater availability of CO2 for the reaction.