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

Many ambient desorption/ionization mass spectrometry (ADI-MS) techniques rely critically on thermal desorption. Mean-while, the analyte classes which are successfully studied by any particular ADI-MS 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 more suitable for molecules with small molar masses. In the present work, classic atmos-pheric-pressure chemical ionization (APCI), is used. To provide improved desorption performance for APCI, a surface acous-tic 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 signif-icantly improves ion signal by up to four-orders of magnitude, reaching comparable ion abundances to electrospray ioniza-tion (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 non-polar small molecules, and novel peptides that mimic biomolecules upwards of 1000 Da. Ob-served 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 ap-proaches.