Probing surfaces of atmospherically relevant organic particles by easy ambient sonic-spray ionization mass spectrometry (EASI-MS)

Wingen, L. M.; Finlayson-Pitts, Barbara J.

doi:10.1039/c8sc03851a

Cited by 16 publications

(21 citation statements)

References 122 publications

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“…Limited surface extraction, approximately 2-4 nm in depth, of the analyte particles has been reported for some ESI source designs (Kumbhani et al, 2018;Wingen and Finlayson-Pitts 2019). If such an effect were present in the EESI-TOF design 250 used in the current study, it could also appear as a size-dependent sensitivity.…”

Section: Influence Of Analyte Particle Coating Thickness On Eesi Sensitivitymentioning

confidence: 65%

Effects of Aerosol Size and Coating Thickness on the Molecular Detection using Extractive Electrospray Ionization

Lee¹,

Surdu²,

Bell³

et al. 2021

Preprint

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Abstract. Extractive electrospray ionization (EESI) is a well-known technique for high throughput online molecular characterization of chemical reaction products and intermediates, detection of native biomolecules, in vivo metabolomics, and environmental monitoring with negligible thermal and ionization-induced fragmentation for over two decades. However, the EESI extraction mechanism remains uncertain. Prior studies disagree whether analyte particles between 20 and 400 nm diameter are fully extracted or if the extraction is limited to the surface layer. Here, we examined the analyte extraction mechanism by assessing the influence of analyte particle size and coating thickness on the detection of the molecules therein. We find that analyte particles are extracted fully: Organics-coated NH4NO3 particles with a fixed core volume (156 and 226 nm in diameter without coating) show constant signals for NH4NO3 independent of the shell coating thickness, while the signals of the secondary organic molecules comprising the shell varied proportionally to the shell volume. We also find that the EESI sensitivity exhibits a strong size dependence, with an increase in sensitivity by one to three orders of magnitude as analyte particle size decreases from 300 nm to 30 nm. This dependence varies with the electrospray (ES) droplet size and the analyte particle residence time in the EESI inlet, suggesting that the EESI sensitivity is influenced by the coagulation rates between analyte particles and ES droplets. Overall, our results indicate that, in the EESI, analyte particles are fully extracted by the ES droplets regardless of the chemical composition, when they are collected by the ES droplets. However, their coalescence is not complete and depends strongly on their size. This size-dependence is especially relevant when EESI is used to probe size-varying analyte particles as is the case in aerosol formation and growth studies with size ranges below 100 nm, while it does not significantly influence the detection of ambient aerosol dominated by particle sizes ranging between 100–2500 nm, i.e. the accumulation mode.

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Section: Influence Of Analyte Particle Coating Thickness On Eesi Sensitivitymentioning

confidence: 65%

Effects of Aerosol Size and Coating Thickness on the Molecular Detection using Extractive Electrospray Ionization

Lee¹,

Surdu²,

Bell³

et al. 2021

Preprint

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“…14,[33][34][35] Additionally, surface sensitivity has been achieved by 97 using extractive electrospray ionization to desorb and ionize molecular species from the aerosol 98 interface. 36,37 Surface-sensitivity has also been achieved using nonlinear spectroscopic techniques, such as second harmonic scattering from free aerosol particles 38 or sum frequency generation from aerosol collected onto a filter substrates. 39,40 However, there are few online, universally surface sensitive measurements that can measure the formation and dissipation of chemical gradients within a particle in situ.…”

mentioning

confidence: 99%

Using Nanoparticle X-ray Spectroscopy to Probe the Formation of Reactive Chemical Gradients in Diffusion-Limited Aerosols

Jacobs

Kostko

et al. 2019

J. Phys. Chem. A

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For aerosol particles that exist in highly viscous, diffusion-limited states, steep chemical gradients are expected to form during photochemical aging in the atmosphere. Under these conditions species at the aerosol surface are more rapidly transformed than molecules residing in the particle interior. To examine the formation and evolution of chemical gradients at aerosol interfaces, the heterogeneous reaction of hydroxyl radicals (OH) on ~200-nm particles of pure squalane (a branched, liquid hydrocarbon) and octacosane (a linear, solid hydrocarbon), and binary mixtures 21 of the two are used to understand how diffusion limitations and phase separation impact particle 22 reactivity. Aerosol mass spectrometry is used to measure the effective heterogeneous OH uptake 23 coefficient (γeff) and oxidation kinetics in the bulk, which are compared with the elemental composition of the surface obtained using X-ray photoemission. When diffusion rates are fast 25 relative to the reaction frequency, as is the case for squalane and low viscosity squalane-octacosane mixtures, the reaction is efficient (γeff ~ 0.3) and only limited by the arrival of OH to the interface. However, for cases where the diffusion rates are slower than reaction rates, as in pure octacosane and higher viscosity squalane-octacosane mixtures, the heterogeneous reaction occurs in a mixinglimited regime and is ~10x slower (γeff ~ 0.03). This is in contrast to carbon and oxygen K edge Xray absorption measurements that show that the octacosane interface is oxidized much more rapidly than that of pure squalane particles. The O:C ratio of the surface (estimated to be the top 6-8 nm of the interface) is measured to change with a rate constant of (3.0±0.9)x10-13 and (8.6±1.2)x10-13 cm 3 molecule-1 s-1 for squalane and octacosane particles, respectively. The differences in surface oxidation rates are analyzed using a previously published reaction diffusion model, which suggests that a 1-2 nm highly oxidized crust forms on octacosane particles, whereas in pure squalane the reaction products are homogenously mixed within the aerosol. This work 37 illustrates how diffusion limitations can form particles with highly oxidized surfaces even at 38 relatively low oxidant exposures, which is in turn expected to influence their microphysics in the 39 atmosphere. 40

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“…Due to the soft ionization of EASI (which does not require the application of heat, high voltages, laser beams or UV light), the reaction products remain intact during the ionization process. [36][37][38][39] As shown in Fig. S4, S5 and S6, the fleeting intermediates of TPrA, including TPrA •+ (its half-life was estimated to 200 µs) 26 and [Pr 2 N=CHCH 2 CH 3 ] + , were detected and characterized.…”

Section: Electrooxidation Of Tri-n-propylaminementioning

confidence: 94%

Mass spectrometric detection of fleeting neutral intermediates generated in electrochemical reactions

Liu

Zhang

et al. 2021

Chem. Sci.

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Probing surfaces of atmospherically relevant organic particles by easy ambient sonic-spray ionization mass spectrometry (EASI-MS)

Abstract: EASI-MS is a promising technique for probing the chemical structures of inhomogeneous airborne organic particles.

Cited by 16 publications

References 122 publications

Effects of Aerosol Size and Coating Thickness on the Molecular Detection using Extractive Electrospray Ionization

Effects of Aerosol Size and Coating Thickness on the Molecular Detection using Extractive Electrospray Ionization

Using Nanoparticle X-ray Spectroscopy to Probe the Formation of Reactive Chemical Gradients in Diffusion-Limited Aerosols

Mass spectrometric detection of fleeting neutral intermediates generated in electrochemical reactions

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