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Comparison of Heated Electrospray Ionization and Nanoelectrospray Ionization Sources Coupled to Ultra-High-Resolution Mass Spectrometry for Analysis of Highly Complex Atmospheric Aerosol Samples
journal contribution
posted on 2020-05-25, 04:49 authored by I. Kourtchev, P. Szeto, I. O’Connor, O. A. M. Popoola, W. Maenhaut, J. Wenger, M. KalbererDirect infusion analysis
using soft ionization techniques coupled
to ultra-high-resolution mass spectrometers (UHRMS) allows screening
of thousands of organic species in complex samples. Despite the high
analytical throughput of direct infusion, this technique is known
to be prone to matrix effects caused by changes in the ionization
efficiency of an analyte, ion suppression, or enhancement due to the
presence of certain compounds and inorganic salts in the sample. In
this study we compared two soft ionization sources, that is, heated
electrospray ionization (HESI) and nano-ESI for the analysis of atmospheric
aerosol samples in the negative ionization mode. In-source fragmentation
tests were conducted and experiments involving sample desalting through
solid-phase extraction (SPE) with a reversed phase functionalized
polymeric sorbent and spiking samples with inorganic salt were performed.
Both ionization sources showed specific advantages and disadvantages
for the direct infusion analysis of atmospheric aerosol extracts.
The mass spectra of aerosol samples analyzed using HESI contained
a large number of high molecular weight homologues containing sulfur
and nitrogen, suggesting that this source is prone to formation of
salt adducts and noncovalent compounds in samples enriched with inorganic
salts. Data from the same aerosol sample extracts analyzed using nanoelectrospray
ionization (nano-ESI) show less adduct formation; however, a decrease
in the number of homologues was observed, as well as loss of molecules
at higher mass range, indicating that the nano-ESI source is more
prone to ion suppression. Irrespective of ionization source, SPE pretreatment
significantly improved ion recoveries for organic species with nonpolar
and moderately polar functional groups, but lower recoveries were
obtained for highly oxygenated molecules. Therefore, while SPE reduced
in-source adduct formation, it also limited the range of compounds
identified through a single analysis.
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Ultra-High-Resolution Mass Spectrometryionization sourcesSPEinfusion analysiscompoundaerosol samplesHESIUHRMSnano-ESIion suppressionin-source adduct formationComplex Atmospheric Aerosol SamplesNanoelectrospray Ionization Sourcesultra-high-resolution mass spectrometersHeated Electrospray Ionizationaerosol sample extractsIn-source fragmentation tests
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