Revisiting benzene cluster cations for the chemical ionization of dimethyl sulfide and select volatile organic compounds

Abstract

Abstract. Benzene cluster cations were revisited as a sensitive and selective reagent ion for the chemical ionization of dimethyl sulfide (DMS) and a select group of volatile organic compounds (VOCs). Laboratory characterization was performed using both a new set of compounds (i.e., DMS, β-caryophyllene) as well as previously studied VOCs (i.e., isoprene, α-pinene). Using a field deployable chemical-ionization time-of-flight mass spectrometer (CIToFMS), benzene cluster cations demonstrated high sensitivity (> 1 ncps ppt −1 ) to DMS, isoprene, and α-pinene standards. Parallel measurements conducted using a chemicalionization quadrupole mass spectrometer, with a much weaker electric field, demonstrated that ion-molecule reactions likely proceed through a combination of ligandswitching and direct charge transfer mechanisms. Laboratory tests suggest that benzene cluster cations may be suitable for the selective ionization of sesquiterpenes, where minimal fragmentation (< 25 %) was observed for the detection of β-caryophyllene, a bicyclic sesquiterpene. The in-field stability of benzene cluster cations using CI-ToFMS was examined in the marine boundary layer during the High Wind Gas Exchange Study (HiWinGS). The use of benzene cluster cation chemistry for the selective detection of DMS was validated against an atmospheric pressure ionization mass spectrometer, where measurements from the two instruments were highly correlated (R 2 > 0.95, 10 s averages) over a wide range of sampling conditions.

Air‐Sea exchange of biogenic volatile organic compounds and the impact on aerosol particle size distributions

“…Underway measurements of surface chlorophyll a in the sampling region during October and November 2013 were on average 1.59 mg m −3 (Figure a). DMS, isoprene, and sum monoterpenes mixing ratios ( C a ) were measured using benzene cluster cation chemical ionization time‐of‐flight mass spectrometry (CI‐ToFMS) [ Bertram et al ., ; Kim et al ., ]. Air‐sea vertical fluxes ( F ) were determined via the eddy covariance method, where 5–10 Hz measurements of mixing ratios were correlated with motion‐corrected vertical wind velocity ( w ) to compute F as…”

“…The first was the University of Hawaii's atmospheric pressure ionization mass spectrometer with an isotopically labeled standard [Blomquist et al, 2010]. The second was the CI-ToFMS, which also measured isoprene and total monoterpene vertical fluxes [Kim et al, 2016]. We showed previously that DMS mixing ratio measurements from the two instruments were in strong agreement (R 2 > 0.95) [Kim et al, 2016].…”

An electrospray chemical ionization source for real-time measurement of atmospheric organic and inorganic vapors

“…In CIMS, the analyte molecule reacts with a specific reagent ion via one or more mechanisms, including ligand switching reaction forming an ion-molecule adduct (Huey et al, 1995;Kercher et al, 2009;Aljawhary et al, 2013;Lee et al, 2014;Farmer, 2015, 2016), proton addition (abstraction) forming a protonated (de-protonated) ion (Nowak et al, 2002;Veres et al, 2008;Yatavelli et al, 2012;Aljawhary et al, 2013;Farmer, 2015, 2016;Yuan et al, 2016), or by direct charge transfer forming a molecular ion (Huey et al, 1995;Kim et al, 2016). The reagent ions used mainly include I − , NO − 3 , acetate, CF 3 O − , and SF − 6 for negative ion CIMS, and H 3 O + , NO + , protonated ethanol, and benzene cation for positive ion CIMS.…”

Styrene radical cations for chemical ionization mass spectrometry analyses of monoterpene hydrocarbons

“…Application of C 8 H 8 +• cannot be compared directly with benzene and benzene cluster cations CIMS by Kim et al and Lavi et al due to the two orders of magnitude higher pressure in their reactor. From the similarity of their molecular structures and IEs it can be expected that C 8 H 8 +• will react with monoterpenes mostly in a similar fashion under higher pressure.…”

“…Recently, NH 4 + reagent ions were introduced in the SRI‐TOF‐MS, Selective Reagent Ionization Time‐of‐Flight, instrumentation, where their reaction with limonene results in formation mostly of the NH 4 + C 10 H 16 adduct ions while protonated molecules are the main products with other studied monoterpenes . Another sensitive CIMS approach has been implemented using benzene and benzene dimer cations reacting with monoterpenes in a reactor operating at 100 mbar . An advantage of this technique is not only its higher sensitivity, but also the good match of the relatively low 8.6 eV benzene dimer ionization energy (IE) to the range of monoterpene IEs (e.g.…”