Decoding Surface-Bound Isomers: A QIT-ToF-SIMS Platform Integrating Tandem Mass Spectrometry and Laser Spectroscopy

A quadrupole-ion-trap-integrated time-of-flight secondary ion mass spectrometry (QIT-ToF-SIMS) system was developed to enable detailed molecular surface analysis via tandem mass spectrometry combined with laser photodissociation spectroscopy. In this approach, secondary molecular ions were selectively isolated in the ion trap using the stored waveform inverse Fourier-transform technique and subsequently subjected to collision-induced dissociation or photoinduced dissociation. Using isomeric rhodamine dyes as model systems, structurally diagnostic fragment ions were observed, allowing for clear molecular identification despite identical nominal masses. The laser photodissociation spectra obtained for the isolated ions revealed a distinct wavelength-dependent fragmentation behavior, consistent with known gas-phase absorption profiles. Because of the integration of tandem mass spectrometry and laser spectroscopy with time-of-flight secondary ion mass spectrometry, the QIT-ToF-SIMS system serves as an effective tool for molecular-level surface characterization, which is particularly well suited for probing increasingly complex organic materials and interfaces.