Knöller Kay, Boettger Tatjana, Haupt Marika, Weise Stephan M
UFZ - Helmholtz Centre for Environmental Research, Theodor-Lieser-Strasse 4, D06120 Halle, Germany.
Rapid Commun Mass Spectrom. 2007;21(18):3085-92. doi: 10.1002/rcm.3183.
The determination of isotope ratios of non-exchangeable hydrogen in tree-ring cellulose is commonly based on the nitration of wood cellulose followed by online high-temperature pyrolysis and isotope ratio mass spectrometry measurement of cellulose nitrate samples. The application of this method requires a proper calibration using appropriate reference materials whose delta(2)H values have been reliably normalized to the V-SMOW/SLAP scale. In our study, we achieve this normalization by a direct alternating measurement of reference waters (V-SMOW and SLAP) and three cellulose nitrates chosen as reference materials. For that purpose, both water and solid organic samples are introduced into the pyrolysis reactor by silver capsule injection. The analytical precision of the water measurement using the capsule method is +/-1.5 per thousand. The hydrogen isotopic composition of three cellulose nitrate standards measured ranges from -106.7 to -53.9 per thousand. The standard deviation of the calculated means from five measurement periods of those standards is better than 1 per thousand. Twenty-four different measurements of the hydrogen isotope composition of cellulose nitrate were evaluated in order to assess the precision of the described method. We obtained an analytical precision of +/-3.0 per thousand as representative for the 95% confidence interval applicable for routine measurements of cellulose nitrate samples. Evidence was found for significant differences in the behavior of cellulose nitrate and PE foil during the pyrolitic conversion that emphasizes the need for a proper calibration of the routine measurements. This calibration can only be successful if the reference materials used have a very similar chemical composition and undergo the same preparation procedure as the samples.
树木年轮纤维素中不可交换氢的同位素比率测定通常基于木材纤维素的硝化，随后进行在线高温热解，并对硝酸纤维素样品进行同位素比率质谱测量。该方法的应用需要使用适当的参考物质进行适当校准，这些参考物质的δ(2)H值已可靠地归一化到V-SMOW/SLAP标度。在我们的研究中，我们通过直接交替测量参考水（V-SMOW和SLAP）以及三种被选作参考物质的硝酸纤维素来实现这种归一化。为此，水和固体有机样品都通过银胶囊注入引入热解反应器。使用胶囊法测量水的分析精度为±1.5‰。所测量的三种硝酸纤维素标准品的氢同位素组成范围为-106.7至-53.9‰。这些标准品在五个测量周期内计算平均值的标准偏差优于1‰。为了评估所述方法的精度，对硝酸纤维素的氢同位素组成进行了24次不同的测量。我们获得了±3.0‰的分析精度，作为适用于硝酸纤维素样品常规测量的95%置信区间的代表。发现在热解转化过程中硝酸纤维素和PE箔的行为存在显著差异，这强调了对常规测量进行适当校准的必要性。只有当所使用的参考物质具有非常相似的化学成分并且与样品经历相同的制备程序时，这种校准才能成功。
