ANALYTICAL DEVELOPMENT FOR THE STABILITY OF SUB-PPM NITROGEN OXIDE (NOX) MIXTURES IN CYLINDERS

Introduction

NO_X is a generic term for a group of reactive gases containing both Nitrogen and Oxygen in varying amounts. These gases are released into the atmosphere when fossil fuels (coal, gasoline…) are burned at high temperature. The main sources of NO_X are motor vehicles, electric utilities, and other industrial, residential, and commercial sources that burn fuel. NO_X has been identified as the primary cause for the formation of ground-level ozone, which leads to serious respiratory problems. It is also responsible for a variety of other health and environmental hazards such as acid rain, global warming, toxic chemicals and atmospheric particle formation. (1)

As a result, many countries and organizations around the world are increasingly regulating NO_X emissions to the atmosphere. The primary regulations aim at drastically decreasing the amount of NO_X released, especially by engines used in transportation and utility/industrial/residential boilers. Therefore, professionals not only have to find ways of limiting and/or controlling NO_X emissions, but prior to that they must have reliable and precise means of measuring ever-decreasing concentrations. In this perspective, there have been considerable efforts by instrument manufacturers to lower detection limits to sub-ppm levels. Also important are the availability and reliability of the standards used to calibrate those instruments. In this paper, a method for low-level NO_X analysis using a Nitrogen Chemiluminescence Detector coupled to a Gas Chromatograph (GC-NCD system) is developed. Finally, a proprietary cylinder treatment developed for the storage of low-level reactive compounds is shown to be successful in storing ppb levels of Nitrogen Oxide (NO) and Nitrogen Dioxide (NO₂) for at least 11 months and 4 months respectively.