Selective measurements of isoprene and 2-methyl-3-buten-2-ol based on NO<sup>+</sup> ionization mass spectrometry

Abstract

Biogenic VOC emissions are often dominated by 2-methyl-1,3-butadiene (isoprene) and 2-methyl-3-buten-2-ol (232 MBO). Here we explore the possibility for selectively distinguishing these species using NO⁺ as primary ion based on PTR-MS technology. High purity of NO⁺ (>90%) as a primary ion was achieved in laboratory and field experiments using a PTR-TOF-MS. Isoprene is ionized via charge transfer leading to the major product ion C₅H₈⁺ (>99%) (e.g. Spanel and Smith, 1998). 232 MBO undergoes a hydroxide ion transfer reaction resulting in the major product ion channel C₅H₉⁺ (>95%) (e.g. Amelynck et al., 2005). We show that both compounds are ionized with little fragmentation (<5%) under standard PTR-MS operating conditions. Typical sensitivities of 11.1&plusmn;0.1 (isoprene) and 12.9&plusmn;0.1 (232 MBO) ncps ppbv^&minus;1 were achieved, which correspond to limit of detections of 18 and 15 pptv, respectively for a 10 s integration time. Sensitivities decreased at higher collisional energies. Calibration experiments showed little humidity dependence. We tested the setup at a field site in Colorado dominated by ponderosa pine, a 232 MBO emitting plant species. Our measurements confirm 232 MBO as the dominant biogenic VOC at this site, exhibiting typical average daytime concentrations between 0.2–1.4 ppbv. The method is able to detect the presence of trace levels of isoprene (90–250 ppt) without any interference from 232 MBO, which would not be feasible using H₃O⁺ ionization chemistry, and which currently also remains achallenge for other analytical techniques (e.g. gas chromatographic methods)

Canopy level emissions of 2-methyl-3-buten-2-ol, monoterpenes, and sesquiterpenes from an experimental Pinus taeda plantation

“…Their total within-canopy vertical profile isoprene mixing ratios ranged from 1.5-2.1 ppbv, and isoprene oxidation products (methyl vinyl ketone + methacroleine) ranged from 2.0-1.7 ppbv. However, the PTR-MS used in that study could not distinguish MBO from isoprene (Karl et al, 2012). Based on our above canopy isoprene and MBO observations, we suspect that a significant fraction of the isoprene reported by Stroud et al (2005) may have actually been MBO, although their vertical mixing ratio profiles (Fig.…”

Isoprene emissions and impacts over an ecological transition region in the U.S. Upper Midwest inferred from tall tower measurements

“…Several previous studies have pointed out that isoprene measurements by quadrupole PTR‐MS at m / z 69 can be subject to interferences from (i) other biogenic VOCs such as 2‐methyl‐3‐buten‐2‐ol (232‐MBO) [ de Gouw and Warneke , ; Karl et al ., ], (ii) furan in biomass burning plumes [ Christian et al ., ], (iii) a variety of alkenes and cycloalkanes in urban air and oil/gas extraction areas [ de Gouw et al ., ; Yuan et al ., ; Warneke et al ., ], and (iv) C5 compounds such as pentenols and methylbutanal emitted via plant wounding during harvesting [ Karl et al ., ]. There is also known to be a small anthropogenic source of isoprene and MVK + MACR associated with tailpipe emissions [ McLaren et al ., ; Borbon et al ., ; Park et al ., ; von Schneidemesser et al ., ; Wang et al ., ; Wagner and Kuttler , ].…”

Tracing coffee origin by direct injection headspace analysis with PTR/SRI-MS

“…PTR-MS has been widely used in food science and technology especially for fingerprinting and profiling of food products (Biasioli, Yeretzian, Gasperi, & Märk, 2011;Biasioli, Yeretzian, Märk, Dewulf, & Van Langenhove, 2011). Besides, PTR/SRI-MS system has been recently applied for detection of isoprene (Karl et al, 2012) and ethylene emissions, in drug research (Acton et al, 2014;Lanza et al, 2013) and homeland Food Research International 69 (2015) [235][236][237][238][239][240][241][242][243] security and lastly in food science for product discrimination (Sánchez del Pulgar et al, 2013). To the best of the authors' knowledge no studies have been published so far on the application of SRI system for geographical origin discrimination of food products and in particular: coffee.…”