Improved method for determining the stable-hydrogen isotopic composition (δD) of complex organic materials of environmental interest

Despite new and increasing applications in environmental studies, determinations of the stable-hydrogen isotope (delta D) composition of complex organic substrates are hampered by laborious preparation techniques and uncontrolled isotopic exchange between labile hydrogen in the sample and ambient water vapor. To date, there has been little agreement in the way laboratories prepare, measure,and correct for uncontrolled hydrogen isotopic exchange in complex organic samples, resulting in incomparable delta D results. Previously, nitration and preparative equilibration procedures aimed at controlling exchangeable hydrogen were designed for specific sample types (e.g, cellulose, chitin) but required extensive processing of individual samples. Here we describe a static, high-temperature preparative equilibration technique that provides increased sample throughput and delta D measurements that are not compromised by uncontrolled isotopic exchange. By adopting this approach, it will be possible to compare complex organic delta D measurements among laboratories. The current inconsistency in organic delta D measurements among laboratories seriously hampers comparison of results among studies. As pyrolitic continuous-flow delta D analyses become available, the preparative equilibration method described can be adapted to suit the smaller size requirements.