Direct Current Arc Plasma-Excited Nebulizer Gas-Assisted Electrospray Ionization Mass Spectrometry

This study demonstrates that a pulsed direct current (DC) arc can simultaneously initiate the electrospray process and generate reagent ions, establishing a pulsed electrospray ionization (ESI) source that operates without a dedicated external ESI high-voltage supply. Generation of an arc plasma between the capillary, serving as the discharge electrode, and a counter electrode substantially increases the excitation energy of the nebulizing gas (NG), enhancing ionization efficiency. This process fundamentally differs from plasma-assisted ESI, in which plasma acts as an auxiliary ionization enhancer rather than as the primary driver of electrospray formation. In DC arc plasma-excited NG-assisted ESI (DCAPENG-ESI), the electrospray process is driven exclusively by the pulsed arc, which supplies the charge and energy required for ion formation. This process enables the formation of distinctive ionization pathways, including Penning ionization and proton transfer, which enhances the ionization of low-polarity compounds and improves salt tolerance in mass spectrometry (MS). Using argon as the NG, the DCAPENG-ESI-MS produces mass spectra with high signal-to-noise ratios and minimal background noise. Methodological validation using six plasticizers demonstrated good linearity (correlation coefficient >0.994) over the concentration range of 0.1-50 μg mL^-1, with a low limit of detection of 0.01 μg mL^-1, and satisfactory recoveries of 82.4%-118.7%. Overall, DCAPENG-ESI demonstrates promise as a simple, robust, and broadly adaptable ionization platform.