Analytical Sciences

A Microporous Membrane-Based Continuous Generation System for Trace-Level Standard Mixtures of Atmospheric Gases

Yukio KANDA,* Masafumi TAIRA,* Kazuhiko CHIMURA,** Tomoyuki TAKANO,** and Motoaki SAWABE**

*High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
**Nisshin Service Co. Ltd., 2-15-7 Amakubo, Tsukuba, Ibaraki 305-0005, Japan

A reliable and convenient system to generate accurate and stable standard gas mixtures of various atmospheric compounds at parts-per-billion levels has been developed. The system is of simple design; the generator is a coil consisting of an inner tube of microporous polytetrafuluoroethylene (PTFE) membrane tubing and an outer tube of silicone tubing. An aqueous solution of the given compound continuously flows through the inner microporous tube and the purge gas flows through the annulus between the inner and outer tubes. In addition to the generation of gas mixtures based on Henry’s law, the proposed flow-type system offers generation based on chemical reactions, leading to a distinct advantage of the availability of continuous sources of various compounds. The generation system was tested for preparing standard gas mixtures of HCHO and H₂O₂ on the basis of Henry’s law, and those of HNO₂, NO, and SO₂ on the basis of chemical reactions. A stable generation of the desired low concentrations of various kinds of gas mixtures can be readily achieved by adjusting the concentration of the solution without the use of high-dilution flow.

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