Abstract
Abstract. We present an electrospray ion source coupled to an orthogonal continuous-flow atmospheric pressure chemical ionization region. The source can generate intense and stable currents of several specific reagent ions using a range of salt solutions prepared in methanol, thereby providing both an alternative to more common radioactive ion sources and allowing for the generation of reagent ions that are not available in current chemical ionization mass spectrometry (CIMS) techniques, such as alkaline cations. We couple the orthogonal electrospray chemical ionization (ESCI) source to a high-resolution time-of-flight mass spectrometer (HR-ToF-MS), and assess instrument performance through calibrations using nitric acid (HNO3), formic acid (HCOOH), and isoprene epoxydiol (trans-β-IEPOX) gas standards, and through measurements of oxidized organic compounds formed from ozonolysis of α-pinene in a continuous-flow reaction chamber. When using iodide as the reagent ion, the HR-ToF-ESCIMS prototype has a sensitivity of 11, 2.4, and 10 cps pptv−1 per million counts per second (cps) of reagent ions and a detection limit (3σ, 5 s averaging) of 4.9, 12.5, and 1.4 pptv to HNO3, HCOOH, and IEPOX, respectively. These values are comparable to those obtained using an iodide-adduct HR-ToF-CIMS with a radioactive ion source and low-pressure ion–molecule reaction region. Applications to the α-pinene ozonolysis system demonstrates that HR-ToF-ESCIMS can generate multiple reagent ions (e.g., I−, NO3−, acetate, Li+, Na+, K+, and NH4+) having different selectivity to provide a comprehensive molecular description of a complex organic system.
Highlights
The Earth’s atmosphere contains thousands of inorganic and organic species that, through complex free radical and multiphase chemistry, play a vital role in air quality and climate change (Finlayson-Pitts and Pitts, 2000; Seinfeld and Pandis, 2006; Goldstein and Galbally, 2007)
Our results demonstrate that the electrospray chemical ionization (ESCI) source provides a potential alternative to radioactive and X-ray ion source and opens a new avenue for the generation of reagent ions such as Li+, Na+, K+, and so on that were previously unavailable for chemical ionization mass spectrometry (CIMS)
We report an electrospray chemical ionization (ESCI) source coupled to a HR-ToF-MS for the real-time online measurement of atmospheric organic and inorganic species in the gas phase
Summary
The Earth’s atmosphere contains thousands of inorganic and organic species that, through complex free radical and multiphase chemistry, play a vital role in air quality and climate change (Finlayson-Pitts and Pitts, 2000; Seinfeld and Pandis, 2006; Goldstein and Galbally, 2007). Compared to I−, NO−3 , and acetate, which are generally more sensitive to more oxygenated organic compounds than to less oxygenated ones (Aljawhary et al, 2013; Lee et al, 2014; Hyttinen et al, 2015; Iyer et al, 2016; Berndt et al, 2016), these metal cations are expected to be able to sensitively detect both less oxygenated (e.g., compounds containing only carbonyl groups) and highly oxygenated multi-functional organic species (Gao et al, 2010; Nguyen et al, 2010; Nizkorodov et al, 2011; Laskin et al, 2012; Witkowski and Gierczak, 2013; Zhao et al, 2015, 2016; Tu et al, 2016; Zhang et al, 2017), and to form more strongly bound ion adducts. Our results demonstrate that the ESCI source provides a potential alternative to radioactive and X-ray ion source and opens a new avenue for the generation of reagent ions such as Li+, Na+, K+, and so on that were previously unavailable for CIMS
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