Stability of PPB and PPM Organic Cylinder Gases Used for Calibration and Audits

Abstract

A repository of 39 and 34 gaseous organic compounds in compressed gas cylinders at PPM (5 to 700) and PPB levels (1 to 10,000) respectively has been established by EPA for use in performance audits. In this program, to ensure that the concentration of each gas standard has not changed, each standard is periodically analyzed for stability. The gas mixtures were initially analyzed once or twice by the manufacturer before shipment to Research Triangle Institute (RTI). The gas mixtures were then analyzed at RTI upon receipt from the gas manufacturer and then reanalyzed at 2, 6 and 12 months, and annually thereafter, to determine any change in concentration.

An examination of the stability data shows that concentrations for all the organics tested usually varied by less than 10 percent over a period of several years. Ethylene oxide and propylene oxide and trans 1, 4-dichloro-2-butene below the 10 ppb level have been found to be unstable. Six other compounds at the PPM level (aniline, cyclohexanone, p-dichlorobenzene, ethylamine 1, 2-dibromoethylene, and formaldehyde) have been found to be unstable in compressed gas cylinders.