Volatilizable Biogenic Organic Compounds (VBOCs) with two dimensional Gas Chromatography-Time of Flight Mass Spectrometry (GC b×/b GC-TOFMS): sampling methods, VBOC complexity, and chromatographic retention data

摘要

Two dimensional gas chromatography (GC × GC) with detection bytime-of-flight mass spectrometry (TOFMS) was applied in the rapid analysisof air samples containing highly complex mixtures of volatilizable biogenicorganic compounds (VBOCs). VBOC analytical methodologies are brieflyreviewed, and optimal conditions are discussed for sampling with bothadsorption/thermal desorption (ATD) cartridges and solid-phasemicroextraction (SPME) fibers. Air samples containing VBOC emissions fromleaves of two tree species (Cedrus atlantica and Calycolpus moritzianus) were obtained by both ATD and SPME. Theoptimized gas chromatographic conditions utilized a 45 m, 0.25 mm I.D. low-polarityprimary column (DB-VRX, 1.4 μm film) and a 1.5 m, 0.25 mm I.D. polarsecondary column (StabilwaxTM, 0.25 μm film).Excellent separation was achieved in a 36 min temperature programmedGC × GC chromatogram. Thousands of VBOC peaks were present in thesample chromatograms; hundreds of tentative identifications by NIST massspectral matching are provided. Very few of the tentatively identifiedcompounds are currently available as authentic standards. Minimum detectionlimit values for a 5 l ATD sample were 3.5 pptv (10 ng m?3) forisoprene, methyl vinyl ketone, and methacrolein, and ~1.5 pptv(~10 ng m?3) for monoterpenes and sesquiterpenes. Kovats-typechromatographic retention index values on the primary column and relativeretention time values on the secondary column are provided for 21 standardcompounds and for 417 tentatively identified VBOCs. 19 of the 21 authenticstandard compounds were found in one of the Cedrus atlantica SPME samples. In addition,easily quantifiable levels of at least 13 sesquiterpenes were found in anATD sample obtained from a branch enclosure of Calycolpus moritzianus. Overall, the resultsobtained via GC × GC-TOFMS highlight an extreme, and largelyuncharacterized diversity of VBOCs, consistent with the hypothesis thatsesquiterpenes and other compounds beyond the current list of typicallydetermined VBOC analytes may well be important contributors to globalatmospheric levels of organic particulate matter.