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

Abstract

Abstract. Two dimensional gas chromatography (GC × GC) with detection by time-of-flight mass spectrometry (TOFMS) was applied in the rapid analysis of air samples containing highly complex mixtures of volatilizable biogenic organic compounds (VBOCs). VBOC analytical methodologies are briefly reviewed, and optimal conditions are discussed for sampling with both adsorption/thermal desorption (ATD) cartridges and solid-phase microextraction (SPME) fibers. Air samples containing VBOC emissions from leaves of two tree species (Cedrus atlantica and Calycolpus moritzianus) were obtained by both ATD and SPME. The optimized gas chromatographic conditions utilized a 45 m, 0.25 mm I.D. low-polarity primary column (DB-VRX, 1.4 μm film) and a 1.5 m, 0.25 mm I.D. polar secondary column (StabilwaxTM, 0.25 μm film). Excellent separation was achieved in a 36 min temperature programmed GC × GC chromatogram. Thousands of VBOC peaks were present in the sample chromatograms; hundreds of tentative identifications by NIST mass spectral matching are provided. Very few of the tentatively identified compounds are currently available as authentic standards. Minimum detection limit values for a 5 l ATD sample were 3.5 pptv (10 ng m−3) for isoprene, methyl vinyl ketone, and methacrolein, and ~1.5 pptv (~10 ng m−3) for monoterpenes and sesquiterpenes. Kovats-type chromatographic retention index values on the primary column and relative retention time values on the secondary column are provided for 21 standard compounds and for 417 tentatively identified VBOCs. 19 of the 21 authentic standard compounds were found in one of the Cedrus atlantica SPME samples. In addition, easily quantifiable levels of at least 13 sesquiterpenes were found in an ATD sample obtained from a branch enclosure of Calycolpus moritzianus. Overall, the results obtained via GC × GC-TOFMS highlight an extreme, and largely uncharacterized diversity of VBOCs, consistent with the hypothesis that sesquiterpenes and other compounds beyond the current list of typically determined VBOC analytes may well be important contributors to global atmospheric levels of organic particulate matter.

Optimization of a gas chromatographic unit for measuring BVOCs in ambient air

“…A list of 20 targeted species was selected for various reasons: some are observed to be the most abundant species at the global scale (isoprene, β-pinene, α-pinene, limonene, trans-β-ocimene, myrcene, sabinene, Δ 3 -carene and camphene) (Guenther et al, 1995;Sindelarova et al, 2014), others are emitted by pine trees (1,8 cineole) (Simon et al, 1994), some are present in pine needles (terpinolene, linalool, α-phellandrene) (Ait Mimoune et al, 2013;Arrabal et al, 2012;Blanch et al, 2012;Kleinhentz et al, 1999;Ormeño et al, 2009;Simon et al, 1994), others are oxidation products, commercially 20 available in pure solution (≥ 95%) of monoterpenes (nopinone, citral), and some are highly reactive (α-terpinene, βcaryophyllene) (Atkinson et al, 2006) or usually monitored along with other BVOCs (p-cymene, γ-terpinene, 2-carene) (Hakola et al, 2017;Jones et al, 2014;Pankow et al, 2012). As only some of the targeted compounds were commercially available in certified gas mixtures (isoprene, β-pinene, α-pinene, limonene, p-cymene, myrcene, Δ 3 -carene, cis-ocimene, 1.8cineole, camphor), a gas mixture containing all the compounds reported previously was consequently generated through the 25 vaporization of pure liquid standards inside an electropolished stainless steel canister.…”

“…Detailed information regarding chemical composition may be obtained by conventional gas chromatographic methods (GC-FID or GC-MS), which can quantify individual terpene isomers (Jones et al 2014;Hopkins et al, 2011;Pankow et al 2012).…”

“…Ambient measurements taking advantage of gas chromatographic techniques usually report isoprene, α-pinene, β-pinene and limonene (Apel et al, 1999;Bouvier-Brown et al, 2009;Greenberg et al, 2004Greenberg et al, , 1999Hopkins et al, 2011;Mallet et al, 2016;Misztal et al, 2010;Saxton et al, 2007) as the major BVOCs. Only a few GC instruments have been optimized to 30 provide a larger speciation of monoterpenes (Pankow et al, 2012;Jones et al, 2014;Hakola et al, 2006Hakola et al, , 2017 and even https://doi.org /10.5194/amt-2019-224 Preprint. Discussion started: 11 July 2019 c Author(s) 2019.…”

“…CC BY 4.0 License. fewer can provide a large speciation of both monoterpenes and oxygenated monoterpenes (Jones et al, 2014;Pankow et al, 2012) (Table 1). Due to their high reactivity, monoterpenes and sesquiterpenes are delicate to quantify.…”

“…Conservation of air samples (in pressured gas canisters or adsorbed on cartridges) for offline analysis of monoterpenes and sesquiterpenes needs to be carefully considered (Apel et al, 1999;Greenberg et al, 2004;Misztal et al, 2010;Pankow et al, 2012). Due to their reactivity or poor stability, certified gas standard mixtures containing multiple terpenes are not readily 15 available, and hence calibration of these gases is generally less straightforward compared to that of other NMHCs.…”