An automated capillary gas chromatographic system to measure ethylene emitted from biological materials is presented. The system consists of an on-line sampling device, a thermodesorption preconcentration apparatus and a capillary gas chromatograph with a flame ionization detection system. The limit of detection achievable on the GC system alone is 5 pg ethylene. The use of the strong Carboxen 1000 adsorbent at a sampling temperature as low as -50 degrees C allows sampling of volumes up to a few liters. Ethylene concentrations at low ppt levels can be accurately and reproducibly determined.