Development and Evaluation of a Thermoelectric Cold Trap for the Gas Chromatographic Analysis of Atmospheric Compounds

A prototype of a thermoelectric cold trap system has been designed, built, and evaluated. The unit is used to preconcentrate trace volatile organic compounds prior to analysis. The thermoelectric cold trap unit provides an alternative to the normally used liquid nitrogen-cooled traps as a means to preconcentrate sampled components. The thermoelectric system is especially applicable in field monitoring programs, where logistical burdens are often encountered when supplying large amounts of liquid cryogens. Likewise, one does not have to be concerned with the expense and downtime associated with the use of liquid cryogens. The thermoelectric cold trap assembly can be easily interfaced with any chromatographic system using a two-position six-port valve. The operating principle is based upon the normal sample adsorption/desorption cycle and GC analysis. The cold trap system includes a custom-designed cold trap module (commercially available thermoelectric module components have been used), an adsorbent tube heater inserted into the cold trap module, and an electronics package to control heating/cooling and timing operations. The cold trap is approximately 15 × 15 × 15 cm. The unit can achieve a cold-side temperature as low as −45 °C under steady-state conditions, and the trap can be heated to 300 °C indefinitely without damaging the thermoelectric modules. The unit also achieves very good transient performances (less than 20 s to heat from −30 to 300 °C and ∼5 min to return to the initial −30 °C set point).