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Hydrogen gas can be produced quantitatively from nanomole amounts of organic H in continuously flowing gas streams. The system described here is suitable for use in isotope-ratio-monitoring mass spectrometric systems and is based on a pyrolysis reactor consisting of a graphitized alumina tube heated to 1450 °C. Methane forms as an intermediate product at temperatures above 750 °C, but, for all tested analytes, yields of H 2 were quantitative at temperatures between 1430 and 1460 °C, provided residence times in the reactor were greater than 300 ms. Quantitative yields of H 2 were obtained for all components of a homologous series of n-alkanes (C 15 to C 30 ). Analyses of low-molecular-weight alcohols demonstrated that O-bound H was also quantitatively converted to H 2 and, thus, that H 2 O, if formed, was quantitatively reduced to H 2 .

Two fundamentally different approaches, termed "pointwise" and "peakwise," are currently used to correct hydrogen isotope ratio monitoring data for the presence of H3+ ion contributions. Consideration of the underlying assumptions shows that the peakwise approach is valid only for peaks with the same functional shape and only when background signals do not vary. The pointwise correction is much more versatile and can be used even when peak shapes and sizes, as well as background signals, vary significantly. It is not exact and is limited in accuracy by (1) the signal-broadening effects of electronic time constants, (2) the analog-to-digital conversion frequency, and (3) the highest frequency of the sample signal. To minimize errors for typical gas chromatographic signals, time constants of <500 ms and analog-to-digital sampling intervals of < or =250 ms are needed. Errors are further minimized by matching sample and standard peaks in both amplitude and D/H ratio. Using the pointwise algorithm, we demonstrate that a series of 14 homologous n-alkanes varying in concentration over a 5-fold range can be analyzed with a mean precision of 2.3 per thousand and no systematic errors.

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