Preparation of Stable Pollution Gas Standards Using Treated Aluminum Cylinders

The use of gas cylinder calibration standards is becoming an increasingly important tool for use in pollution analysis methods requiring a known reference. There are problems, however, in the preparation of pollution gas standards using high pressure steel cylinders. Researchers have documented these problems in the literature, especially in recent months. When reactive gases such as the oxides of nitrogen, carbon monoxide, or sulfur dioxide are blended in a steel cylinder with an inert balance gas, the concentration that the cylinder delivers can vary with time, pressure, and temperature. The nature of the blend's instability is random and a function of the absorption or reaction with the walls of the cylinder. These disturbing features lead to an obvious question. Can the specialty gas industry provide a stable and accurate pollution calibration standard in a cylinder? This paper deals with that question and describes experience gained using treated aluminum cylinders as a solution to the problem. Included in the discussion are: (1) instrumental and analysis method evaluation, (2) calibration and correlation of internal standards, (3) effects of various cylinder types on the stability of reactive gas mixtures, (4) effects of preconditioning as a means of deactivating cylinder walls, (5) effects of variables such as temperature and pressure on cylinder concentrations, and (6) long-term stability data.