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Permeation devices are used in a variety of dynamic gas dilution systems to prepare trace or ultra-trace mixtures of gases and vapors, generally for calibration purposes. The sources of errors in the use of a permeation device for calibration are associated with the reproducibility of flow measurements, temperature control, and the stability of the mass transport characteristics of the permeation device. Since the primary component of such a single or multi-stage trace gas calibration system is the permeation device, then it is befitting that a comprehensive study of the stability and transport properties be undertaken. This paper describes trace calibration systems and the factors that influence their operation. Also presented is COGAS, a dynamic dilution system that serves to calibrate both permeation devices and instruments. Such a system improves precision, reduces manpower requirements, and is versatile in its application.
permeation, gas diffusion, calibration, solubility, dynamic dilution, gas analysis, sulfur dioxide, sampling, air quality, atmospheric measurements
Research chemist, Gas and Particulate Science Division, Center for Analytical Chemistry, National Bureau of Standards, Gaithersburg, MD