HILL RESEARCH LAB Isoprene Analysis by Ion Mobility Spectrometry-Mass Spectrometry

1. Department of Chemistry Hill Research Group Ion Mobility Spectrometry HILL RESEARCH LAB Isoprene Analysis by Ion Mobility Spectrometry-Mass Spectrometry Trimer ABOUT THE PROJECT Dimer Monomer • This is a multidisciplinary project in collaboration with Dr. Hal Westberg and Jack Chen, from the Department of Civil and Environmental Engineering. • The project involves measuring and modeling biogenic Volatile Organic Compounds (BVOC) emissions from vegetation. • The goal is to understand the role of BVOC in regional atmospheric chemistry and terrestrial carbon exchange related to the global carbon cycle and climate change. Figure 4. 2D-IM-MS plot of isoprene ions, shown with mobility drift times and mass-to-charge ratios Figure 5. Ion mobility spectra of isobaric monoterpenes at 200ºC Figure 1. Ion mobility spectrometer coupled to a time-of-flight mass spectrometer INTRODUCTION • Isoprene is one of the most important naturally emitted volatile organic compounds (VOC) in the atmosphere. It accounts for more than a third of globally annual VOC emissions. It plays a significant role in atmospheric photochemistry through facilitating the production of pollutants such as ground level ozone and secondary organic aerosols. • Detecting isoprene in ambient air requires continuous measurement with sub ppbv detection limit, a large linear dynamic range, and a high selectivity. For micrometeorlogical flux measurements atop forest canopies, fast instrument response of 10 analysis per second is necessary. • This study aims to demonstrate that IMS alone can be used for field flux measurements to rapidly detect and separate isoprene from monoterpenes. Figure 2. Mass-selected ion mobility spectra of isoprene at low concentration Figure 3. Mass-selected ion mobility spectra of isoprene at high concentration Figure 6. Mass-selected ion mobility spectra of isobaric isoprene dimer, -pinene and myrcene at 200ºC (Rp 75) and 150ºC (Rp 85) RESULTS CONCLUSION METHODS • Experimental data demonstrated the ability of IMS to separate isoprene and monoterpenes. • The monomeric isoprene (K0 = 2.35 cm2 V-1 s-1 ) was observed for the first time by IMS (Figure 2). • Dimer, trimer, and tetramer ions of isoprene were also detected. Pentamer ions were observed at higher sample concentrations (Figure 3). • The mass-mobility trend line of isoprene ions is shown in Figure 4. • The mobility time of the four monoterpenes analyzed were very similar (Figure 5). Separation between monoterpenes would require ultra-high resolution-IMS. • As the IMS temperature decreased, the resolving power (Rp) of IMS increased, allowing for the separation of the isobaric isoprene dimer and monoterpenes (Figure 6). • A stand-alone IMS has the capability of separating isoprene from monoterpenes, with fast signal response that is suitable for micro-meteorlogical flux measurements. Isoprene 68Da • Head space sample vapor was directed into the ion mobility spectrometer (IMS) by a flow of nitrogen gas and ionized by secondary electrospray ionization (SESI). • The samples analyzed were isoprene, myrcene, -pinene, R-(+)-limonene, and 3-carene. The structures of these compounds are shown on the right. • The ion mobility spectrometry-mass spectrometry (IMS-MS) system consisted of an electrospray ionization (ESI) source, an IMS coupled to a 150 QC ABB Extrel quadrupole mass spectrometer (QMS), or an Ionwerks orthogonal time-of-flight mass spectrometer (TOF-MS). Myrcene 136 Da -Pinene 136 Da R-Limonene 136 Da 3-Carene 136 Da Camping trip with collaborators