Determination of dissolved methane in natural waters using headspace analysis with cavity ring-down spectroscopy
Determination of dissolved methane in natural waters using headspace analysis with cavity ring-down spectroscopy
复制标题
使用腔衰荡光谱法顶空分析测定天然水中溶解的甲烷
DOI：
10.1016/j.aca.2014.10.058
复制
发表时间：
2015
影响因子：
6.2
通讯作者：
Shiller, Alan M.
中科院分区：
文献类型：
--
作者：
Roberts, Hannah M.;Shiller, Alan M.
甲烷（CH4）是第三大温室气体（GHG），但与二氧化碳相比，人们对它的研究远远不足。对大气的源和汇的估计差别很大，包括淡水和海水系统等源。评价了一种测定离散水样中溶解甲烷浓度的新方法。利用激光腔衰落光谱（CRDS）分析平衡顶空，可测定低纳摩尔溶解甲烷浓度，重现性高（即检测限为0.13 nM，典型RSD为4%）。虽然CRDS仪器的成本大约是通常用于甲烷测定的气相色谱仪（GC）的两倍，但本文提出的过程比GC方法更简单，更快，所需材料更少。通常，70毫升的水样在塑料注射器中与等量的零空气平衡。平衡后的顶空被转移到一个干净、干燥的注射器中，然后通过仪器的泵吸入Picarro G2301 CRDS分析仪。我们证明，该仪器保持线性校准到亚ppmv甲烷浓度范围，并保持稳定校准至少两年。介绍了该方法在墨西哥湾北部船舶溶解甲烷测定和河水测定中的应用。用这种方法测定了近6个数量级的浓度。
Methane (CH4) is the third most abundant greenhouse gas (GHG) but is vastly understudied in comparison to carbon dioxide. Sources and sinks to the atmosphere vary considerably in estimation, including sources such as fresh and marine water systems. A new method to determine dissolved methane concentrations in discrete water samples has been evaluated. By analyzing an equilibrated headspace using laser cavity ring-down spectroscopy (CRDS), low nanomolar dissolved methane concentrations can be determined with high reproducibility (i.e., 0.13 nM detection limit and typical 4% RSD). While CRDS instruments cost roughly twice that of gas chromatographs (GC) usually used for methane determination, the process presented herein is substantially simpler, faster, and requires fewer materials than GC methods. Typically, 70-mL water samples are equilibrated with an equivalent amount of zero air in plastic syringes. The equilibrated headspace is transferred to a clean, dry syringe and then drawn into a Picarro G2301 CRDS analyzer via the instrument’s pump. We demonstrate that this instrument holds a linear calibration into the sub-ppmv methane concentration range and holds a stable calibration for at least two years. Application of the method to shipboard dissolved methane determination in the northern Gulf of Mexico as well as river water is shown. Concentrations spanning nearly six orders of magnitude have been determined with this method.