Thermal Desorption Comprehensive Two-Dimensional Gas Chromatography: An Improved Instrument for In-Situ Speciated Measurements of Organic Aerosols

Abstract

The organic fraction is a major constituent of fine atmospheric particulate matter, though its chemical composition is complex and not well understood. This complexity presents an extreme analytical challenge and is well suited to analysis by comprehensive twodimensional gas chromatography (GC × GC). This has recently been coupled to a thermal desorption aerosol gas (TAG) chromatograph instrument to provide improved in-situ, hourly measurement of speciated organic compounds in atmospheric aerosols (2D-TAG). The original 2D-TAG instrument utilized a flame ionization detector, dual-stage modulator, and a second-dimension column that proved to be thermally unstable under optimal analysis conditions, which limited compound identification, instrument robustness, and time resolution. In this paper, we address these shortcomings by demonstrating the successful integration of a time-of-flight mass spectrometer (TOFMS), development of a simplified hybrid thermo-pneumatic modulator, and incorporation of a more thermally stable secondary column. These improvements resulted in an instrument capable of providing detailed speciated information of organic tracer compounds in atmospheric aerosols in near real time.

Evaluation of sequential solvent and thermal extraction followed by analytical pyrolysis for chemical characterization of carbonaceous particulate matter

“…Several attempts were made to characterize OM using thermal methods coupled to either GC or GC × GC [22][23][24][25][26]. Streibel et al obtained promising results for recognition of various semi-volatile species in PM using sequential thermal extraction (TE) with direct MS detection [27].…”

Organic aerosol composition and sources in Pasadena, California, during the 2010 CalNex campaign

“…Measurements of refractory black carbon (rBC) were performed with a Single Particle Soot Photometer (Droplet Measurement Technologies) [Schwarz et al, 2006], as well as with a Soot Particle Aerosol Mass Spectrometer (SP-AMS; Aerodyne Research and Droplet Measurement Technology) [Onasch et al, 2012]. The concentrations of semivolatile and particulate organic molecular tracers were measured by 2-D Thermal Desorption Aerosol Gas Chromatography Mass Spectrometry (2DTAG; UC-Berkeley and Aerosol Dynamics) [Worton et al, 2012]. PM 2.5 nitrate and sulfate concentrations were measured with a ParticleInto-Liquid Sampling and Ion Chromatography (PILS-IC) system [Orsini et al, 2003].…”

The First Combined Thermal Desorption Aerosol Gas Chromatograph—Aerosol Mass Spectrometer (TAG-AMS)

“…Additionally, ambient phase-transitioning of semivolatile organic compounds has been estimated from TAG measurements (Williams et al 2010b), and recently, a semivolatile TAG instrument has been developed to separately quantify the gas-phase and particle-phase fraction of semivolatile organic compounds . Finally, comprehensive two-dimensional (GCxGC) gas chromatography and time-of-flight mass spectrometry (ToFMS) has been added to the TAG collector to allow for greater molecular separation (i.e., greater than an order of magnitude more species separated) and increased sensitivity (Goldstein et al 2008;Worton et al 2012). This 2D-TAG instrument has recently been used in laboratory-based controlled chamber experiments (Isaacman et al 2011a) and ambient air sampling during the CalNex 2010 campaign (Hayes et al 2013).…”