An approach for the determination of formaldehyde produced during the electrochemical oxidation of methanol over fuel cell catalyst materials is described. Sample electrolysis is conducted in a small volume (0.050 mL) cavity machined into a Macor glass ceramic disk. The working electrode is positioned adjacent to the cavity in a manner that entraps solution. The cavity is equipped with a port that enables sample to be injected and removed. The arrangement is presented in studies of methanol oxidation over bulk and nanoscale PtRu fuel cell catalyst materials. A fluorescence assay is employed to determine formaldehyde in these experiments with a detection limit down to 100 nM. This is an abstract of a paper presented at the 230th ACS National Meeting (Washington, DC 8/28/2005-9/1/2005).