Rhoderick George C, Yen James H
Analytical Chemistry Division and Statistical Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8393, USA.
Anal Chem. 2006 May 1;78(9):3125-32. doi: 10.1021/ac052136r.
Primary gravimetric gas cylinder standards containing 30 volatile organic compounds (VOCs) in nitrogen were prepared using a procedure previously developed to prepare gas mixture cylinder standards of VOCs at the 5 nmol/mol level. This set of primary standards was intercompared to existing gas cylinder standards, containing as many as 19 of the 30 volatile organics present in these new primaries, using gas chromatography with a hydrogen flame ionization detector coupled with cryogenic preconcentration. The linear regression analysis showed excellent agreement among the standards for each compound. Similar mixtures containing many of these compounds in treated aluminum gas cylinders have been evaluated over time and have shown stability for as much as 10 years. The development of these 30-component primary standards led to the preparation and certification of a reissue of Standard Reference Material (SRM) 1804 at the nominal amount-of-substance fraction of 5 nmol/mol for each analyte. A lot of 20 cylinders containing the mixture was prepared at NIST following previously demonstrated protocols for preparation of the cylinders. Each cylinder was analyzed against one cylinder from the lot, designated as the "lot standard," for each of the 30 compounds. As a result of the uncertainty analysis, the data showed that rather than declaring the lot homogeneous with a much higher uncertainty, each cylinder could be individually certified. The expanded uncertainty limits ranged from 1.5 to 10% for 28 of the 30 analytes, with two of the analytes having uncertainties as high as 19% in those SRM cylinders certified. Due to stability issues and some high uncertainties for a few analytes in 2 of the samples, 18 of the 20 candidate SRM samples were certified. These volatile organic gas mixtures represent the most complex gas SRMs developed at NIST.
使用先前开发的程序制备了含30种挥发性有机化合物（VOCs）的氮气中主要重量法气瓶标准物质，该程序用于制备5 nmol/mol水平的VOCs气体混合物气瓶标准物质。使用配有氢火焰离子化检测器和低温预浓缩装置的气相色谱法，将这组主要标准物质与现有的气瓶标准物质进行了比对，现有气瓶标准物质中含有这些新主要标准物质中30种挥发性有机物中的多达19种。线性回归分析表明，各化合物的标准物质之间具有极佳的一致性。随着时间的推移，对经过处理的铝质气瓶中含有许多这些化合物的类似混合物进行了评估，结果表明其稳定性长达10年。这30种成分主要标准物质的研制促成了标准参考物质（SRM）1804的重新制备和认证，每种分析物的标称物质分数为5 nmol/mol。按照先前演示的气瓶制备方案，在国家标准与技术研究院（NIST）制备了一批20个装有该混合物的气瓶。针对这30种化合物中的每一种，对每个气瓶与该批次中指定为“批次标准”的一个气瓶进行了分析。不确定性分析结果表明，数据显示，与其以高得多的不确定性宣称该批次均匀一致，不如对每个气瓶进行单独认证。30种分析物中的28种的扩展不确定度范围为1.5%至10%，在那些经认证的SRM气瓶中，有两种分析物的不确定度高达19%。由于稳定性问题以及2个样品中少数分析物存在一些高不确定性，20个候选SRM样品中有18个获得了认证。这些挥发性有机气体混合物代表了NIST研制的最复杂的气体标准参考物质。
