Dorgerloh Ute, Becker Roland, Theissen Hubert, Nehls Irene
BAM Federal Institute for Materials Research and Testing, Berlin, Germany.
J Environ Monit. 2010 Oct 6;12(10):1876-84. doi: 10.1039/c0em00091d. Epub 2010 Aug 23.
A number of currently recommended sampling techniques for the determination of hydrogen in contaminated groundwater were compared regarding the practical proficiency in field campaigns. Key characteristics of appropriate sampling procedures are reproducibility of results, robustness against varying field conditions such as hydrostatic pressure, aquifer flow, and biological activity. Laboratory set-ups were used to investigate the most promising techniques. Bubble stripping with gas sampling bulbs yielded reproducible recovery of hydrogen and methane which could be verified for groundwater sampled in two field campaigns. The methane content of the groundwater was confirmed by analysis of directly pumped samples thus supporting the trueness of the stripping results. Laboratory set-ups and field campaigns revealed that bubble stripping of hydrogen may be restricted to the type of used pump. Concentrations of dissolved hydrogen after bubble stripping with an electrically driven submersible pump were about one order of magnitude higher than those obtained from diffusion sampling. The gas chromatographic determination for hydrogen and methane requires manual injection of gas samples and detection by a pulsed discharge detector (PDD) and allows limits of quantification of 3 nM dissolved hydrogen and 1 µg L⁻¹ dissolved methane in groundwater. The combined standard uncertainty of the bubble stripping and GC/PDD quantification of hydrogen in field samples was 7% at 7.8 nM and 18% for 78 nM.
针对现场作业的实际熟练程度，对目前推荐的多种用于测定受污染地下水中氢气的采样技术进行了比较。合适采样程序的关键特性包括结果的可重复性、对不同现场条件（如静水压力、含水层流动和生物活性）的稳健性。利用实验室装置对最具前景的技术进行了研究。使用气体采样球泡进行鼓泡吹扫，可实现氢气和甲烷的可重复回收，这在两次现场作业采集的地下水中得到了验证。通过对直接抽取的样品进行分析，证实了地下水中的甲烷含量，从而支持了吹扫结果的真实性。实验室装置和现场作业表明，氢气的鼓泡吹扫可能受所用泵的类型限制。使用电动潜水泵进行鼓泡吹扫后，溶解氢的浓度比扩散采样所得浓度高约一个数量级。氢气和甲烷的气相色谱测定需要手动进样气体样品，并使用脉冲放电检测器（PDD）进行检测，对于地下水中溶解氢的定量限为3 nM，溶解甲烷的定量限为1 μg L⁻¹。现场样品中氢气鼓泡吹扫和气相色谱/脉冲放电检测器定量的合成标准不确定度在7.8 nM时为7%，在78 nM时为18%。
