A large-radius high-mass-resolution multiple-collector isotope ratio mass spectrometer for analysis of rare isotopologues of O-2, N-2, CH4 and other gases

作者：Young Edward D^*; Rumble Douglas III; Freedman Philip; Mills Mark

来源：International Journal of Mass Spectrometry, 2016, 401: 1-10.

DOI：10.1016/j.ijms.2016.01.006

• Isotope ratios
• Mass spectrometry
• Mass-resolution
• Rare isotopologues
• Methane
• Oxygen

We describe a unique and novel isotope ratio mass spectrometer (IRMS), the Panorama, developed explicitly for high-mass-resolution analysis of isotopologue ratios of gas samples. The double-focussing instrument routinely operates at a mass resolving power of 40,000 with a maximum useful MRP of similar to 80,000. The instrument achieves this exceptional MRP for a multi-collector using a Matsuda ion optical design with an ESA radius of 1018 mm and a magnetic sector radius of 800 mm. Collectors comprise 9 Faraday cups and a single channel of ion counting each with continuously variable collector slits. First results demonstrate both accuracy and precision comparable to, and in some cases, surpassing, other gas-source multi-collector IRMS instruments for singly-substituted species. For example, accurate bulk D/H and C-13/C-12 for methane gas measured with CH4 as the analyte are measured simultaneously with internal precision of 0.02-0.04 parts per thousand (1 std error) and similar to 0.006 parts per thousand (1 se), respectively. Ion counting with continuous rebalancing of sample and standard gases permits high-precision measurements of rare, multiply-substituted isotopologues with relative abundances as small as similar to 0.1 ppm. In the case of methane, both (CH3D)-C-13/(CH4)-C-12 and (CH2D2)-C-12/(CH4)-C-12 ratios are measured with precision of similar to 0.1 parts per thousand and similar to 0.5 parts per thousand, respectively. Accuracy of the multiply-substituted species measurements is demonstrated using isotope ratio mixing experiments. The ability to measure both Delta(CH3D)-C-13 and Delta CH2D2 (parts per thousand variations relative to the stochastic reference frame) provides heretofore unmatched capabilities to identify kinetic reaction pathways, isotope fractionation during transport, mixing, as well as temperatures of formation for methane gas. The high-resolution instrument can be used for a wide variety of applications. For example, it easily resolves Ar-36(+) from (OO+)-O-18-O-18 for oxygen bond-ordering studies. It also easily resolves (NO+)-N-14-O-16 from (NN+)-N-15-N-15 for measurements of the doubly-substituted N-2 species.

• 出版日期2016-4-25