Thermal Desorption is a reagent-free analytical method that is applied here to ethylene detection. Carbosieve SIII is used to adsorb ethylene from prepared standards and humid air. Air samples are drawn through glass-lined steel tubes filled with the trapping material. Ethylene and other light hydrocarbons trapped from the air are then desorbed in a single step directly into a GC inlet for analysis. Large concentration factors in the samples make routine detection of less than 1 ppb ethylene possible without major modification of the chromatograph.
Sample size is limited only by the breakthrough volume of the adsorbent.
Additionally, the method is useful for other light hydrocarbons such as propylene and isoprene that must be accurately measured in very low concentration. However, this method is limited by the amount of gas that can be reliably introduced into the GC inlet. Even recent advances in column technology have kept detection limits for ethylene in the low ppm range without the use of expensive specialized detectors. One serious deficiency is the tendency for linearity to fall off dramatically at the lower limits of detection. An alternative to static headspace measurement is the dynamic enrichment, or trapping technique.