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.

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The concept of direct mass-spectrometric analysis, especially exploited by ambient desorption/ionization (ADI) methods, provides numerous means for convenient sample analysis. While many simple and versatile ionization sources have been developed, challenges lay in achieving efficient sample introduction. In previous work, a sample introduction method employing direct current corona discharge (CD) coupled to a surface acoustic wave nebulization (SAWN) device enhanced sampling performance for both polar and nonpolar analytes by up to 4 orders of magnitude. In fact, the SAWN-CD method generated a multiply charged peptide ion signal comparable to that of conventional ESI. Unfortunately, the high cost of the SAWN devices themselves limits their accessibility. Herein, we report on an analogous implementation of CD with an inexpensive ultrasonic nebulizer (USN) on the basis of a commercial room humidifier demonstrating equivalent exemplary performance. We subsequently compare the two methods of SAWN-CD and USN-CD in a screening application of milk for the detection of two antibiotic drugs, ciprofloxacin and ampicillin. Finally, we further investigate the relative softness of these CD-coupled acoustic nebulization methods in comparison to that of ESI using a survival yield study of the thermometer ion nitrobenzylpyridinium.

Herein, DART ionization was coupled to DMS to demonstrate their combined utility and compatibility for rapid separation and characterization of new psychoactive substances.