Kelley Michael E, Rhoderick George C, Guenther Franklin R
Gas Metrology Group, Chemical Sciences Division, Materials Measurement Laboratory, National Institute of Standards and Technology , 100 Bureau Drive, MS8393, Gaithersburg, Maryland 20899-8393, United States.
Anal Chem. 2014 May 6;86(9):4544-9. doi: 10.1021/ac500581b. Epub 2014 Apr 22.
The Gas Metrology Group at the National Institute of Standards and Technology (NIST) became active in developing primary standards at ambient levels of N2O in the 1980s, and this has continued through to the present. In recent years, interest in NIST-traceable standards has increased-not only at the ambient level of approximately 325 nmol mol(-1) (ppb) but at micromole per mole (ppm) levels as well. In order to support two in-process dry whole air standard reference materials (SRMs 1720 and 1721) and the NIST Traceable Reference Materials (NTRM) program, a project was implemented in the Gas Metrology Group to produce a complete suite of new primary standard materials (PSMs) of N2O with synthetic air (O2/N2) as the balance gas. Six levels of dilution, approximately 1 order of magnitude apart, were gravimetrically prepared and verified. Each level serves as the "parent mix" for the next level. This discussion describes the process of producing each level and then verifying its amount-of-substance fraction. Expanded uncertainties, k = 2, of 0.025% relative to the gravimetric amount-of-substance fraction were obtained at the ambient level. One standard from the final group of standards at the ambient amount-of-substance fraction level was compared with standards from the National Oceanographic and Atmospheric Administration and the Scripps Institution of Oceanography, two organizations experienced in gas standards preparation and ambient whole air measurements, and shows agreement to 0.07 nmol mol(-1) (0.02% relative) and 0.20 nmol mol(-1) (0.06% relative), respectively.
美国国家标准与技术研究院（NIST）的气体计量小组于20世纪80年代开始积极开发环境水平一氧化二氮的一级标准，且这一工作一直持续至今。近年来，对可溯源至NIST的标准的需求有所增加，不仅在约325 nmol mol⁻¹（ppb）的环境水平，在微摩尔每摩尔（ppm）水平也是如此。为了支持两种过程中的干燥全空气标准参考物质（SRM 1720和1721）以及NIST可溯源参考物质（NTRM）计划，气体计量小组实施了一个项目，以生产一套完整的以合成空气（O₂/N₂）作为平衡气体的新型一氧化二氮一级标准物质（PSM）。通过重量法制备并验证了六个稀释水平，相邻水平之间相差约一个数量级。每个水平作为下一个水平的“母混合液”。本讨论描述了制备每个水平并随后验证其物质的量分数的过程。在环境水平下，相对于重量法物质的量分数获得了k = 2时0.025%的扩展不确定度。将环境物质的量分数水平的最终一组标准中的一个标准与美国国家海洋和大气管理局以及斯克里普斯海洋学研究所的标准进行了比较，这两个组织在气体标准制备和环境全空气测量方面经验丰富，结果分别显示一致性为0.07 nmol mol⁻¹（相对0.02%）和0.20 nmol mol⁻¹（相对0.06%）。
