Design variants of an integrated vacuum electrochemical reactor (IVER) have been developed and utilized to achieve the isotopic quantitation of select electroactive materials. The platinum-electrode IVER module can facilitate chemical prereaction, solution degas, electrolytic gas generation, and gas containment prior to mass spectrometric analysis. Batch specimens of oxalic acid -C-13(2) and sodium pyruvate-1-C-13, each > 99 atom % C-13, were measured by IVER-mass spectrometry (MS) to approximately 0.1 atom % of their precursor C-13-enrichment values. Likewise, batch specimens of neat water -O-18, each > 95 atom % O-18, were suitably analyzed using IVER-MS technology. Operational reproducibility was +/- 0.02 atom % isotope for both 13-carbon-and 18-oxygen-enriched analytes of interest. No ancillary electrolyte was required during the vacuum electrolyses of water-O-18 and oxalic acid-C-13(2). As expected, sequential analyses of the electrogenerated hydrogen gas from a starting quantity of formic acid-H-2(2) solution showed progressive increases in the H-2 enrichment as the remaining solution in the reactor was repeatedly degassed and electrolyzed. (c) 2008 The Electrochemical Society.