Department of Earth, Atmospheric and Planetary Sciences , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States.
Center for Atmospheric and Environmental Chemistry , Aerodyne Research, Inc. , Billerica , Massachusetts 01821 , United States.
Anal Chem. 2019 Dec 3;91(23):14967-14974. doi: 10.1021/acs.analchem.9b03412. Epub 2019 Nov 12.
We present precise measurements of doubly deuterated methane (CHD) in natural methane samples using tunable infrared laser direct absorption spectroscopy (TILDAS). Using a 413 m optical path length astigmatic Herriott cell and two quantum cascade lasers (QCLs) scanning the spectral regions of 1090.46 ± 0.1 and 1200.23 ± 0.1 cm, the instrument simultaneously measures the five main isotopologues of methane. The ratios CHD/CH and CHD/CH are measured at 0.01‰ and 0.5‰ (1σ) instrumental precision, respectively. The instrumental accuracy was assessed by measuring a series of methane gases with a range of δC and δD values but with the abundances of all isotopologues driven to thermal equilibrium at 250 °C. The estimated accuracy of ΔCHD is 1‰ (1σ) on the basis of the results of the heated methane samples. This new TILDAS instrument provides a simple and rapid technique to explore the sources of methane in the environment.
我们使用可调谐红外激光直接吸收光谱（TILDAS）对天然甲烷样品中的双氘代甲烷（CHD）进行了精确测量。该仪器使用 413 米光程散光双曲度惠更斯池和两个量子级联激光器（QCL）扫描 1090.46 ± 0.1 和 1200.23 ± 0.1 cm 的光谱区域，同时测量了甲烷的五个主要同位素。CHD/CH 和 CHD/CH 的比值分别以 0.01‰和 0.5‰（1σ）的仪器精度进行测量。仪器精度通过测量一系列具有不同 δC 和 δD 值但所有同位素丰度在 250°C 下达到热平衡的甲烷气体来评估。根据加热甲烷样品的结果，估计 ΔCHD 的准确度为 1‰（1σ）。这种新的 TILDAS 仪器提供了一种简单快速的技术来探索环境中甲烷的来源。
