Highly Accurate Nitrogen Dioxide (NO2) in Nitrogen Standards Based on Permeation

The development and operation of a highly accurate primary gas facility for the dynamic production of mixtures of nitrogen dioxide (NO2) in nitrogen (N-2) based on continuous weighing of a permeation tube and accurate impurity quantification and correction of the gas mixtures using Fourier transform infrared spectroscopy (FT-IR) is described. NO2 gas mixtures in the range of 5 mu mol mol(-1) to 15 mu mol mol(-1) with a standard relative uncertainty of 0.4% can be produced with this facility. To achieve an uncertainty at this level, significant efforts were made to reduce, identify and quantify potential impurities present in the gas mixtures, such as nitric acid (HNO3). A complete uncertainty budget, based on the analysis of the performance of the facility, including the use of a FT-IR spectrometer and a nondispersive UV analyzer as analytical techniques, is presented in this work. The mixtures produced by this facility were validated and then selected to provide reference values for an international comparison of the Consultative Committee for Amount of Substance (CCQM), number CCQM-K74,(1) which was designed to evaluate the consistency of primary NO2 gas standards from 17 National Metrology Institutes.