A specialized vacuum electrolysis reactor was designed, constructed, and utilized for 13-carbon isotope analysis of formic acid-13C and acetic acid-13C, each highly enriched at the C1-position. This reusable reactor was equipped with two platinum wire electrodes, miniature stir bar, and sidearm reaction chamber. The associated technique developed for 13-carbon isotope analysis is based upon electrolytic generation of carbon dioxide into the preevacuated reactor followed by gas inlet mass spectrometry. It proved practical to degas and electrolyze 95% formic acid (without added electrolyte) due to adequate ionic conductivity. Formic acid-13C (nominally 99 at. % 13C) was measured by electrolytic CO2 generation to be 98.9 at. % 13C. To analyze various 13C-isotopic permutations of acetic acid, lithium and acid were separately added to reactor compartments, vacuum degassed, and stirred to produce an acidic solution. Thus, acetic acid-1-13C that was nominally 99 at. % 13C1 was determined by vacuum electrolysis to be 98.9 at. % 13C1. Further, acetic acid-2-13C that was isotope depleted at the C1-position (and known to be 99 at. % 13C at C2) gave 0.8 at. % 13C by mass spectrometry.

Design variants of an integrated vacuum electrochemical reactor ͑IVER͒ 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-13 C 2 and sodium pyruvate-1-13 C, each Ͼ99 atom % 13 C, were measured by IVER-mass spectrometry ͑MS͒ to approximately 0.1 atom % of their precursor 13 C-enrichment values. Likewise, batch specimens of neat water-18 O, each Ͼ95 atom % 18 O, were suitably analyzed using IVER-MS technology. Operational reproducibility was ±0.02 atom % isotope for both 13-carbonand 18-oxygen-enriched analytes of interest. No ancillary electrolyte was required during the vacuum electrolyses of water-18 O and oxalic acid-13 C 2 . As expected, sequential analyses of the electrogenerated hydrogen gas from a starting quantity of formic acid-2 H 2 solution showed progressive increases in the 2 H enrichment as the remaining solution in the reactor was repeatedly degassed and electrolyzed.

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