Laboratory for Atmospheric Research, Washington State University, Pullman, WA 99164, USA.
Rapid Commun Mass Spectrom. 2009 Dec;23(23):3868-74. doi: 10.1002/rcm.4325.
Developments in continuous-flow isotope ratio mass spectrometry have made possible the rapid analysis of delta13C in CO2 of small-volume gas samples with precisions of < or = 0.1 per thousand. Prior research has validated the integrity of septum-capped vials for collection and short-term storage of gas samples. However, there has been little investigation into the sources of contamination during the preparation and analysis of low-concentration gas samples. In this study we determined (1) sources of contamination on a Gasbench II, (2) developed an analytical procedure to reduce contamination, and (3) identified an efficient, precise method for introducing sample gas into vials. We investigated three vial-filling procedures: (1) automated flush-fill (AFF), (2) vacuum back-fill (VBF), and (3) hand-fill (HF). Treatments were evaluated based on the time required for preparation, observed contamination, and multi-vial precision. The worst-case observed contamination was 4.5% of sample volume. Our empirical estimate showed that this level of contamination results in an error of 1.7 per thousand for samples with near-ambient CO2 concentrations and isotopic values that followed a high-concentration carbonate reference with an isotope ratio of -47 per thousand (IAEA-CO-9). This carry-over contamination on the Gasbench can be reduced by placing a helium-filled vial between the standard and the succeeding sample or by ignoring the first two of five sample peaks generated by each analysis. High-precision (SD < or = 0.1 per thousand) results with no detectable room-air contamination were observed for AFF and VBF treatments. In contrast, the precision of HF treatments was lower (SD > or = 0.2 per thousand). VBF was optimal for the preparation of gas samples, as it yielded faster throughput at similar precision to AFF.
连续流动同位素比质谱技术的发展使得对小体积气体样品中 CO2 的 δ13C 进行快速分析成为可能，其精度可达 < 或 = 0.1‰。先前的研究已经验证了隔垫密封小瓶用于收集和短期储存气体样品的完整性。然而，对于在低浓度气体样品的制备和分析过程中污染的来源，研究甚少。在本研究中，我们确定了：（1）Gasbench II 上的污染来源；（2）开发了一种降低污染的分析程序；（3）确定了一种高效、精确的方法将样品气体引入小瓶。我们研究了三种小瓶填充程序：（1）自动冲洗填充（AFF）；（2）真空回充（VBF）；（3）手动填充（HF）。根据制备所需的时间、观察到的污染程度以及多瓶精度来评估处理方法。观察到的最严重污染是样品体积的 4.5%。我们的经验估计表明，对于 CO2 浓度接近环境水平且同位素值遵循同位素比为-47‰（IAEA-CO-9）的高浓度碳酸盐参考值的样品，这种污染程度会导致误差为 1.7‰。通过在标准和后续样品之间放置一个充满氦气的小瓶，或忽略每次分析产生的五个样品峰中的前两个，可以减少 Gasbench 上的这种夹带污染。对于 AFF 和 VBF 处理，观察到高精度（SD < 或 = 0.1‰）且没有可检测到的室内空气污染的结果。相比之下，HF 处理的精度较低（SD > 或 = 0.2‰）。VBF 是制备气体样品的最佳选择，因为它在类似精度的情况下具有更快的通量。
