Abstract: An enrichment system for volatile organic compounds (VOCs) in ambient air based on adsorbent
 tube sampling/cold trap focusing method was developed. The VOCs in ambient air are sampled
 firstly by the adsorbent tube, and then focused on the cold trap. After the cold trap
 thermal analysis, the VOCs enter the GC-FID system with the high purity carrier gas.
The performance of the system was measured by using standard gases(benzene, methylbenzene,
ethylbenzene). The experimental results show that the cold trap designed by this system
has a focusing efficiency of more than 90\% for VOCs (benzene series), and relative standard deviation 
of standard samples is less than 3\%, and the linear correlation coefficient is greater
than 0.99. The system is stable in operation, and satisfies the demand for enrichment of VOCs in the ambient air.

Key words: volatile organic compounds in ambient air, adsorbent tube sampling , cold trap focusing, thermal analysis, GC-FID