HIGH-SPEED ISOTHERMAL ANALYSIS OF ATMOSPHERIC ISOPRENE AND DMS USING ONLINE 2-DIMENSIONAL GAS-CHROMATOGRAPHY

An instrument has been developed that allows rapid measurements of two of the most important volatile organic species in the atmosphere. The method utilizes two-dimensional gas chromatography coupled to a progr ammed temperature vaporization injector used for sample pre-concentrat ion and injection. Attention is paid to the determination of atmospher ic concentrations of isoprene (the most reactive hydrocarbon species) and dimethyl sulfide (DMS), the major source of sulfur in the marine t roposphere and a precursor to cloud formation. A sorbent packed liner placed inside a programmed temperature vaporization injector was held subambiently by means of a Peltier device during sample collection. Th ermal desorption is performed and the analytes passed to a primary col umn, separating with respect to analyte vapor pressure. Selected linea r or ''heart-cut'' transfer is performed to a second column where the final separation is performed with respect to chemical functionality. Both primary and secondary separations are performed under isothermal conditions with carrier pressure programming used to improve speed of analysis. Primary column backflush and concurrent sample acquisition d uring the secondary analysis are also used to keep analysis cycle time s to a minimum. Total time for sample collection and analysis is aroun d 10 min, with an instrument peak power consumption of 400 W and a min imum detectable limit of 5 ppt for isoprene and 25 ppt for DMS.