Purity analysis of benzene, toluene, ethyl benzene and xylenes (BTEX) for preparation of condensable gas standards by gas chromatography.

摘要

The gas metrology laboratory of the National Metrology Institute of South Africa (NMISA) has embarked on a project to develop methodology for the preparation of condensable gas standards of ethanol, as well as benzene, toluene, ethylbenzene and xylene isomers (BTEX) in nitrogen. The aim is to provide reliable calibration of instruments such as gas analysers and gas chromatographs (GCs), by ensuring measurement traceability to national measurement standards. Volatile organic compounds (VOCs) are important because of their detrimental effects on human health. Typical VOCs that occur in the atmosphere that constitute a health risk are benzene, toluene, xylene, aldehydes, 1,3-butadiene, n-hexane and various chlorinated hydrocarbons. Therefore, high accuracy standards for BTEX in nitrogen are becoming a more important requirement for the monitoring of BTEX at point sources, such as petroleum refineries, filling stations and other similar industries. The purity analysis of these compounds is one of the three most important requirements for the preparation of high accuracy gas standards to be used for air pollution monitoring. This paper will discuss the approach for purity analysis by gas chromatography, as well as the preparation of the BTEX in nitrogen gas standards. These mixtures are prepared gravimetrically using liquid 'loop' injection to the evacuated cylinder.