Automatic monitoring of benzene, toluene and xylenes at PPB level for air quality evaluation

The presence of Benzene and other volatile aromatic hydrocarbons in the environment has been increasing continuously due to mole intensive traffic now and the particular chemical composition of unleaded gasolines. The high toxicity of Benzene is very well known therefore continuous monitoring and the individual measurement of benzene, toluene, ethyl-benzene and xylenes (BTEX), especially in urban areas, has become an important requirement for the protection of public health. In this paper, an on-line monitor for benzene, toluene, ethyl-benzene and xylenes is presented. The system is based on a capillary gas chromatographic technique in which the air sample is continuously pumped through a trap containing a special adsorbent. After sampling, the trap is rapidly heated and the components are introduced into the capillary column system: this consists of a pre-column for the back-flushing of heavier compounds and an analytical column for BTEX separation. A selective detector (PID) assures high selectivity and enough sensitivity to determine BTEX at the ppb level. The monitor has been developed to have a compact design for an easy installation in mobile laboratories or in analyser cabins. Data on reproducibility obtained with a synthetic mixture are reported. BTEX concentrations measured over a period of a week and collected under unattended operation conditions are also reported.