PROGRAMMED-TEMPERATURE VAPORIZATION INJECTION (PTV) FOR IN-SITU FIELD-MEASUREMENTS OF ISOPRENE, AND SELECTED OXIDATION-PRODUCTS IN A EUCALYPTUS FOREST

A technique has been developed to allow for rapid in situ field measur ements of isoprene, methacrolein (MACR), methyl vinyl ketone (MVK) and selected monoterpenes using programmed temperature vaporization injec tion (PTV). As an example of the technique's effectiveness, the result s of a series of ambient air samples taken in a Portuguese eucalyptus forest are presented. Samples were collected on to a sorbent trap, and analysis was performed on site using a programmed temperature vaporis ation injector (PTV) to produce a rapid desorption of analytes from so rbent trap on to a wide bore gas chromatography (GC) column. Using thi s method no intermediate cryofocusing step is required, eliminating th e need for cryogenic coolants. The high flow rate of helium over the s orbent trap during the GC analysis rapidly reconditions the trap which is ready to be reused at the end of the analytical programme. Using a single sorbent trap ambient biogenic compound concentrations from the forest canopy were monitored every 70 min, over a 5 d period.