A fully automated GC-ECD system was constructed to perform unattended on site measurement of airborne halocarbons. To adequately manage water vapor during analysis a retractable thermoelectric cooling device was built and incorporated into the automated GC-ECD system for retaining water vapor during sample preconcentration. This device allows the trap tubing to engage with the cooling block when trapping, or disengage for flash thermal desorption. Thus, no cryogen was needed either in preconcentration or column separation. Unattended continuous hourly measurement of halocarbons was then performed in the field to evaluate effect of water vapor on halocarbon measurement by targeting compounds that are more subject to surface adsorption, such as CCl4. Excellent reproducibility of CCl4 was observed during the measurement period by cooling the trap at 5°C. By contrast, when trapping at 30°C without sufficient water retention the reproducibility of CCl4 suffered greatly, exhibiting an obvious systematic error with the measurement.
- Thermoelectric cooling