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PH21 Semi-Volatile Pollutants in Polar and Alpine Ecosystems
(PH244) The use of conifer needles to monitor atmospheric semi-volatile organic compounds in Sequoia National Park.
Deskin, L.1, Geiser, L.2, Simonich, S.1, 1 Oregon State University, Corvallis, OR, USA2 USDA - Forest Service, Corvallis, OR, USA
ABSTRACT- An analytical method, required to reduce additive interferences of lipids and waxes while maximizing recovery of target analytes, was developed to extract semi-volatile organic compounds (SOCs) from conifer needles. Noble fir (Abies procera) needles were collected and stored at -15 to -20° C in Kapak metalized polyester bags until extraction. Target analytes were spiked onto needles immediately before extraction and labeled surrogates were added at the end of the process to quantitate loss across the method. The first method used accelerated solvent extraction with dichloromethane (DCM) to remove the outer surface of needles. Polar, organic interferences were removed from the extract in DCM by water solvent extraction. The resulting DCM fraction was solvent exchanged to hexane and purified by adsorption chromatography with a 20 g silica column, eluting target analytes in separate fractions using increasingly polar solvents. An improved method dried extracts in DCM over solvent cleaned, oven baked NaSO4 before purification of the extract by gel permeation chromatography (GPC). The fraction from GPC determined to contain target analytes was collected by a fraction collector, purified by adsorption chromatography, and prepared as above. Extracts were screened for interferences using gas chromatography with flame ionization detection and analyzed using electron impact gas chromatography coupled to mass spectroscopy (EI/GCMS) and electron capture negative ionization gas chromatography coupled to mass spectroscopy (ECNI/GCMS). From extracts obtained using the first method, only the least polar fraction from adsorption chromatography was suitable for analysis: 38 of 83 spiked, target analytes were identified. Extracts purified by GPC exhibited significantly lower interference levels: two of three fractions were suitable for analysis with GCMS, with recovery of 64 of 83 target analytes. Method verification was conducted in triplicate to ensure recoveries of 50 – 120%. Improved method was used to analyze SOCs in conifer needles taken from Sequoia National Park.
Key words: passive air sampling, semi-volatile organic compounds, conifer needles
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