A simple headspace equilibration method for measuring dissolved methane
A simple headspace equilibration method for measuring dissolved methane
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DOI：
10.4319/lom.2014.12.637
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发表时间：
2014-09
期刊：
影响因子：
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通讯作者：
C. Magen;L. Lapham;J. Pohlman;K. Marshall;Samantha H Bosman;M. Casso;J. Chanton
中科院分区：
文献类型：
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作者：
C. Magen;L. Lapham;J. Pohlman;K. Marshall;Samantha H Bosman;M. Casso;J. Chanton
海洋中溶解的甲烷浓度与大气接近平衡。由于甲烷在海水中仅微溶，因此在没有污染的情况下测量甲烷对于在空气存在下收集和处理的样品来说是具有挑战性的。文献中描述了几种用于分析溶解甲烷的方法，但没有一种方法对方法产率，收集，运输和储存过程中的污染问题以及温度变化和防腐剂的影响进行了彻底的评估。先前的提取方法通过“喷射和捕集”或“顶部空间平衡”技术将甲烷从水转移到气体。然后通过气相色谱法分析气体中的甲烷。在这里，我们重新审视了顶空平衡技术，并描述了一种简单，廉价，可靠的方法来测量淡水和海水中的甲烷，无论浓度如何。在表面海水中通常发现的浓度范围内（2 - 1000 nmol L-1），该方法的产率接近添加已知量甲烷后溶解度计算预期的100%。除了灵敏度（检测限为0.1 ppmv或0.74 nmol L-1）外，该方法每个样品所需时间不到10分钟，并且不使用剧毒化学品。它可以用最少的材料进行，并且不需要在收集地点使用气相色谱仪。因此，它可以用于各种远程工作环境和条件。
Dissolved methane concentrations in the ocean are close to equilibrium with the atmosphere. Because methane is only sparingly soluble in seawater, measuring it without contamination is challenging for samples collected and processed in the presence of air. Several methods for analyzing dissolved methane are described in the literature, yet none has conducted a thorough assessment of the method yield, contamination issues during collection, transport and storage, and the effect of temperature changes and preservative. Previous extraction methods transfer methane from water to gas by either a "sparge and trap" or a "headspace equilibration" technique. The gas is then analyzed for methane by gas chromatography. Here, we revisit the headspace equilibration technique and describe a simple, inexpensive, and reliable method to measure methane in fresh and seawater, regardless of concentration. Within the range of concentrations typically found in surface seawaters (2‐1000 nmol L‐1), the yield of the method nears 100% of what is expected from solubility calculation following the addition of known amount of methane. In addition to being sensitive (detection limit of 0.1 ppmv, or 0.74 nmol L‐1), this method requires less than 10 min per sample, and does not use highly toxic chemicals. It can be conducted with minimum materials and does not require the use of a gas chromatograph at the collection site. It can therefore be used in various remote working environments and conditions.