Online Characterization of Particles and Gases with an Ambient Electrospray Ionization Source

Abstract

Methods for online characterization and quantification of gas- and particle-phase species greatly facilitate the study of aerosol particle formation and reaction mechanisms. An online method for aerosol analysis has been developed by altering a conventional electrospray ionization mass spectrometer to direct the aerosol flow through the nebulizing gas inlet. Interaction between the aerosol and electrospray droplets produces ions that are subsequently analyzed by MS or MS/MS with a quadrupole ion trap mass analyzer. Performance is assessed using both particle-phase (cesium iodide, glycine) and gas-phase (dimethylamine, dimethylnapthylamine) analytes as well as a secondary organic aerosol (SOA) produced by ozonolysis of α-pinene. Analyte signal intensity is strongly dependent on solubility in the electrospray solvent, suggesting that the predominant ionization mechanism involves extraction of the analyte into the electrospray droplets. For gas-phase analytes, gas-phase charge transfer also appears to play a minor role in ion formation. As currently configured, the source is capable of characterizing oligomers in a SOA at a mass loading of <30 μg/m(3) and quantifying alkyl amine concentrations between approximately 8 ppb and 1 ppm.

Electrodynamic balance–mass spectrometry of single particles as a new platform for atmospheric chemistry research

“…One approach may be to vaporize the particle not with a heated platform, but with an infrared laser, possibly followed by a separate gas-phase ion source (as in Warschat et al, 2015;Westphall et al, 2008;or Zelenyuk et al, 2009). Alternately, an electrospray-type scheme may be used, such as delivering the particle onto a paper spray source (as in Jacobs et al, 2017), ionizing via an interaction between the particle and a spray of ions (e.g., as in Doezema et al, 2012;Gallimore and Kalberer, 2013;or Horan et al, 2012), or by producing a spray directly from the particle when dropped onto a charged needle tip (as in Tracey et al, 2014).…”

Online molecular characterisation of organic aerosols in an atmospheric chamber using extractive electrospray ionisation mass spectrometry

“…An alternative possibility is that offline collection and analysis introduces positive artefacts to the nanoESI(−)-MS spectrum, such as via additional reaction on the substrate. Horan et al (2012) found that the relative abundance of oligomers was also higher in filter samples than their online AESI method, which was attributed to a negative filter sampling artefact -the evaporation of semi-volatile material (predominantly monomers) during collection. However, the overall Figure 5.…”

“…However, a number of studies have detected gas-phase species using an electrospray source -e.g. Horan et al (2012), Wu et al (2000) and Zhao et al (2017a). The ion source design and operating parameters appear important in determining the ionisation efficiency and mechanism (uptake into droplets or gas-phase chemical ionisation).…”

“…Doezema et al (2012) demonstrated an initial application of EESI-MS to organic aerosols, identifying a number of products formed from α-pinene ozonolysis in positive ion mode. Horan et al (2012) reported a related technique for particle-and gasphase chemical characterisation, ambient electrospray ionisation (AESI).…”

A cautionary note on the effects of laboratory air contaminants on ambient ionization mass spectrometry measurements

“…EESI is a soft ionization technique, which in positive ion mode predominantly forms [M + H] + ions. The analyte ion signal intensity is dependent on the analyte solubility, concentration and proton affinity (in positive ion mode), assuming that the experimental configuration is constant …”