Surface Acoustic Wave Nebulization with Atmospheric-Pressure Chemical Ionization for Enhanced Ion Signal

Abstract

Many ambient desorption/ionization mass spectrometry (ADI-MS) techniques rely critically on thermal desorption. Meanwhile, the analyte classes that are successfully studied by any particular ADI-MS methods are strongly dependent on the type of ionization source. Generally, spray-based ionization sources favor polar analytes, whereas plasma-based sources can be used for more hydrophobic analytes and are more suitable for molecules with small molar masses. In the present work, classic atmospheric-pressure chemical ionization (APCI) is used. To provide improved desorption performance for APCI, a surface acoustic wave nebulization (SAWN) device was implemented to convert liquid analytes into fine airborne particles. Compared to conventional SAWN that is used solely as an ionization source for liquid samples, the coupling of SAWN and APCI significantly improves ion signal by up to 4 orders of magnitude, reaching comparable ion abundances to those of electrospray ionization (ESI). Additionally, this coupling also extends the applicable mass range of an APCI source, conventionally known for the ionization of small molecules <500 Da. Herein, we discuss cursory evidence of this applicability to a variety of analytes including both polar and nonpolar small molecules and novel peptides that mimic biomolecules upward of 1000 Da. Observed species are similar to ESI-derived ions including doubly charged analyte ions despite presumably different charging mechanisms. SAWN–APCI coupling may thus involve more nuanced ionization pathways in comparison to other ADI approaches.

Assessing the protective effects of different surface coatings on NaYF4:Yb3+, Er3+ upconverting nanoparticles in buffer and DMEM

“…The injection time was set to 45 ms at 1 micro scan (without hardware averaging). The ionization method used has been previously described 52 . An in-house built device similar to a surface acoustic wave nebulizer (SAWN) was used to introduce the sample in a pulsed fashion.…”

Faster, better, and cheaper: harnessing microfluidics and mass spectrometry for biotechnology

“…When the samples are atomized, fine particles are produced, a small fraction of which then become charged due to microscopic fluctuations in the initial droplet. Recently, SAWN has been combined with other ambient MS ionization techniques such as atmospheric-Pressure chemical Ionization (APCI) 140 and low-temperature plasma ionization (LTPI) 144 to enhance the sensitivity. Unlike other microfluidic methods for sample manipulation, SAWN chip does not require pressure driven pumps or interconnects, nor the integration of microchannels.…”

“…However, the simple geometry of SAWN devices allows potentially attractive combinations with other ionization techniques to potentially improve overall ionization efficiency. 140,144 …”

Unsupervised Reconstruction of Analyte-Specific Mass Spectra Based on Time-Domain Morphology with a Modified Cross-Correlation Approach

“…An ultrasonic nebulizer (USN) was used to generate analyte-containing droplets (1–3 μm diameter based on calculation). , These droplets were transferred through a 26 kHz laser-induced plasma (LIP) in the open air toward the inlet capillary of a high-resolution Orbitrap (Exactive, Thermo Scientific, Bremen, Germany) mass spectrometer through a venturi flow guide ( cf ., Figure S1). Here, the LIP was used as an ionization source, while the USN merely served to introduce samples .…”