Energy-resolved in-source dissociation spectra by tunable pulsed arc plasma ionization for the differentiation of structural isomers

Differentiating structural isomers in mass spectrometry (MS) poses significant challenges due to the difficulties in generating fragment ions by atmospheric pressure ionization and the spectral similarities encountered in tandem MS/MS analysis. The continuous arc plasma enables in-source dissociation fingerprinting analysis of isomers but presents a risk of solvent ignition during sample introduction because of high temperatures, posing safety concerns. To address these challenges, the Tunable Pulsed Arc Plasma (TPAP) ionization and dissociation device has been developed. The TPAP device converts continuous arc plasma into a pulsed mode, reduces plasma temperatures, enhances discharge stability and safety, and enables adjustable plasma energy for in-source compound dissociation. Programmable control over the pulsed arc plasma voltage allows the scanning of compounds under varying dissociation energies, facilitates the construction of compound-specific energy-resolved spectra. Validation experiments with disubstituted benzene species, chlorogenic acid derivatives, disaccharide and diacylglycerol have demonstrated the capability of TPAP-MS to effectively differentiate isomers through distinct energy-resolved spectra. The TPAP-MS requires minimal instrumental modifications and provides rapid and precise structural annotations directly from the ion source, offering broad potential applications in the analysis of structural isomers.