SEDL / STP / STP957-EB / STP25705S

Parts-Per-Billion Gaseous Mixtures: A New Challenge

Denyszyn, RB
Manager, Research and Development, and laboratory technician, Scott Specialty Gases, Plumsteadville, PA

Sassaman, T
Manager, Research and Development, and laboratory technician, Scott Specialty Gases, Plumsteadville, PA

Pages: 9    Published: Jan 1987

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Abstract

Specialty gas manufacturers are being driven by regulatory requirements to manufacture low concentration gaseous mixtures of various air pollutants. This paper describes some of the basic difficulties incurred in preparing parts-per-billion (ppb) concentrations of various volatile organics such as pyridine, Freon^® 113, Freon^® 114, vinylidene chloride, toluene, 1,4 dioxane, acetone, chlorobenzene, acetonitrile, and methylethyl ketone. Concentrations range from 10 to 150 ppb. During the manufacturing and certification of these mixtures, several problems were encountered, including:

1. Ghost peaks due to gas chromatographic system background.

2. Adsorption of compounds in the analytical system as well as on cylinder walls.

3. Difficulties in preparation of primary standards for calibration.

4. Contamination of cylinders, even after special cleaning and preparation.

It is therefore imperative that when purchasing such mixtures, a certificate of analysis as well as a copy of the chromatographs be provided to the user.