Gandhi H, Wiegner T N, Ostrom P H, Kaplan L A, Ostrom N E
Department of Geological Sciences, Michigan State University, East Lansing, MI 48824, USA.
Rapid Commun Mass Spectrom. 2004;18(8):903-6. doi: 10.1002/rcm.1426.
A technique for measurement of the stable isotope composition of dissolved organic carbon (DOC) in stream water, using an elemental analyzer (EA) coupled to an isotope ratio mass spectrometer (IRMS), is described. Stream water samples were concentrated by rotary evaporation, acidified to remove dissolved inorganic carbon (DIC), and dried in silver cups prior to analysis. Precision was evaluated with standards (alanine and humic acid), and with stream water samples with varying (13)C enrichment. Standards and samples were also prepared in sealed quartz tubes for high-temperature combustion (HTC) and analyzed by dual inlet for comparison. The delta(13)C values of natural abundance standards and samples measured by the two techniques differed by <or=0.3 per thousand. Isotopically enriched stream water samples analyzed using the EA and HTC methods had comparable delta(13)C and atom % values (differed by <or=6%). Expensive quartz vessels and the extensive time required for sample lyophilization, combustion and cryogenic separation of combustion products before isotopic analysis for the HTC method are eliminated with the EA method. Overall, the EA method is simpler, faster, and more economical than the HTC method, and it can be used for (13)C-enriched as well as natural abundance samples.
本文描述了一种使用与同位素比率质谱仪（IRMS）联用的元素分析仪（EA）测量溪流水体中溶解有机碳（DOC）稳定同位素组成的技术。溪流水样通过旋转蒸发进行浓缩，酸化以去除溶解的无机碳（DIC），并在银杯中干燥后进行分析。使用标准品（丙氨酸和腐殖酸）以及具有不同（13）C富集度的溪流水样评估精密度。标准品和样品也制备在密封石英管中用于高温燃烧（HTC），并通过双进样口进行分析以作比较。两种技术测量的天然丰度标准品和样品的δ（13）C值相差≤0.3‰。使用EA和HTC方法分析的同位素富集溪流水样具有可比的δ（13）C和原子百分比值（相差≤6%）。EA方法消除了HTC方法中昂贵的石英容器以及样品冻干、燃烧和燃烧产物在同位素分析前的低温分离所需的大量时间。总体而言，EA方法比HTC方法更简单、更快且更经济，并且它可用于（13）C富集以及天然丰度样品。
