IMPROVED RESOLUTION AND DETERMINATION OF AMBIENT C-5-C-12 HYDROCARBONS BY GC-COUPLED REFOCUSING SYSTEM

A homemade cryogenic system derived from readily available material is described, illustrating its usage as an accessory for adsorption/ther mal desorption chromatography. A small Chromsorb-W-HP packing (1 cm) w as introduced into a deactivated precolumn as a cryofocussing, preconc entrating unit. This was able to retain the analyte which had been the rmally desorpted from a Tenax TA sampling tube at a relatively higher temperature (- 80 degrees C similar to - 90 degrees C), with the analy te also reinjected on the analytical column in a relatively narrow ban d. Average overall recoveries for 24 hydrocarbons tested were 97.5 %. Cryofocussing enhanced sensitivity and improved resolution. Field stud ies at a petroleum industry site were carried out and the accessory pr oved to be useful for complex C-5-C-12 hydrocarbon analysis in ambient air.