Direct mass analysis of neutral molecules by superconductivity

Dissociation related to ion collision reactions produces neutral fragments in addition to ionic fragments, and the ability to analyze both neutral and ionic fragments is crucial for fully understanding chemical reactions in the gas phase. However, conventional mass spectroscopy (MS) instruments are unable to directly analyze multiple neutral fragments without reionization. This inability is called “neutral loss.” We report the first tandem MS instrument realized by a kinetic-energy-sensitive cryodetector (a superconducting tunnel junction operated in the Giaever mode) as the second mass separation (KEMS) to quantitatively analyze multiple fragment molecules, either neutral or ionic, in a keV kinetic energy range. The performance of the MS/KEMS instrument was examined using the collisions of singly charged acetone or acetyl precursors with a Xe target. These singly charged ions undergo either collisionally activated dissociation (CAD) or electron transfer dissociation (ETD), including a dissociation path of ABA+ + e → ABA* → A + B + A or AB + A, which produces neutral fragments only. Our approach is able to determine the branching ratios of the competing CAD and ETD processes and may provide a method to overcome the neutral loss.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (125 K)Download as PowerPoint slideResearch highlights▶ Cryodetector compensates neutral loss. ▶ Multiple neutral fragments are separated according to kinetic energies (KEMS). ▶ Direct mass analysis of neutral fragments reveals the competitive dissociation branches of CAD and ETD. ▶ MS/KEMS instrument opens the door to see neutral fragments as they are.