Comprehensive two-dimensional gas chromatography (GC×GC) measurements of volatile organic compounds in the atmosphere

During the MINOS campaign in August 2001 comprehensive two-dimensional gas chromatography (GC×GC) was applied to the in situ measurements of atmospheric volatile organic compounds (VOCs) at the Finokalia ground station, Crete. The measurement system employs a thermal desorption unit for on-line sampling and injection, and a GCxGC separation system equipped with a flame ionization detector (FID) for detection. The system was optimized to resolve C7−C14 organic components. Two-dimensional chromatograms from measurements of Finokalia air samples show several hundred well-separated peaks. To facilitate peak identification, cartridge samples collected at Finokalia were analyzed using the same GC×GC system coupled with a time-of-flight mass spectrometer (TOF-MS). The resulting mass spectra were deconvoluted and compared to spectra from a database for tentative peak identification. About 650 peaks have been identified in the two-dimensional plane, with significant signal/noise ratios (>100) and high spectra similarities (>800). By comparing observed retention indices with those found in the literature, 235 of the identifications have been confirmed. 150 of the confirmed compounds show up in the C7−C14 range of the chromatogram from the in situ measurement. However, at least as many peaks remain unidentified. For quantification of the GCxGC measurements, peak volumes of measured compounds have been integrated and externally calibrated using a standard gas mixture.