A Cryogen-free Refrigerating Preconcentration/Thermal Desorption System for On-line Determination of Volatile Organic Compounds in Ambient Air

A cryogen-free refrigerating preconcentration/thermal desorption system, which uses a refrigeration compressor as a cold source, has been developed, optimized, and characterized. Carbon molecular sieve TDX-01 and graphitized carbon black were used as the adsorbents for enrichment of the C2–C4 fraction of volatile organic compounds (VOCs) at −10 °C. The trapped analytes were thermally desorbed and were transferred directly into the gas chromatography for analysis without the need for a second cryotrap or secondary condensation. The detection limits, at a sampling volume of 500 mL, ranged from 14 to 52 parts per trillion depending on the analytes. Compared with the traditional thermal desorption systems that use liquid nitrogen or thermoelectric coolers as cold sources, this system is more applicable for the rapid analysis of trace VOCs in air, with merits of low cost and low power consumption.