Enhancement of Molecular Ions in Mass Spectrometry Using an Ultrashort Optical Pulse in Multiphoton Ionization

Femtosecond ionization mass spectrometry for chromatographic detection

Mass spectrometry is now in widespread use for the detection of the analytes separated by chromatography. Electron ionization is the most frequently used method in mass spectrometry. However, this ionization technique sometimes suffers from extensive fragmentation of analytes, which makes identification difficult. A photoionization technique has been developed for suppressing this fragmentation and for subsequently observing a molecular ion. A variety of lasers have been employed for the sensitive and selective ionization of organic compounds. A femtosecond laser has a high peak power and is preferential for efficient ionization as well as for suppressing fragmentation, providing valuable information concerning molecular weight and chemical structure as well. In this review, we report on applications of femtosecond ionization mass spectrometry combined with gas chromatography.

Competing Deprotonation and Electron Capture Dissociation in MALDI Mass Spectrometry

A protonation/deprotonation mechanism has been established for the interpretation of ions in MALDI. We show herein that negative ions can be generated in different ways. Molecules with different electron affinities have been spotted on surfaces of TiO₂, ZnO, and a stainless steel plate for the investigation of electron capture dissociation in comparison with photo- or thermal-induced deprotonation upon irradiation of the third harmonic of Nd³⁺:YAG (355 nm) laser pulses. Detection of C60^•- and Fe (II) (porph^•-) radical anions unambiguously demonstrates the electron-transfer process and the exothermic capture of electrons. Radical anions of fatty acids were difficult to observe because of electron-directed ultrafast homolytic cleavage of O-H bonds unless there is a conjugated system as that in C60 and porphyrin for the delocalization and stabilization of acquired changes. The surface basicity of substrate materials was found to determine the competition of the electron-capture dissociation with deprotonation processes. Multiple electron transfers to pyrrole, -COOH, and Fe²⁺ of the heme were observed on TiO₂ and the stainless steel plate but not on ZnO. When the heme was deprotonated by proton sponge 1,8-bis(dimethylamino)naphthalene, the occurrence of electron transfer on TiO₂ was also not observed. It is proposed that negative charges of deprotonated ions prevent electron transfer due to the repulsive force. When both deprotonation and electron transfer are inhibited, adsorbed fatty acids on TiO₂ undergo dehydration reactions to form titanium esters. In contrast, ZnO generates gaseous micelles composed of positive metal ions and negative fatty acid ions through either deprotonation or electron-capture dissociation.

Turn-on Fluorescent Detection of Hydrogen Peroxide and Triacetone Triperoxide via Enhancing Interfacial Interactions of a Blended System

In this work, we report the fabrication of a blend consisting of fluorescent 1 nanofibers and amberlyst-15 particles as a turn-on fluorescence sensor for trace TATP vapors. Fluorescence imaging and lifetime analysis reveal that the interface between 1 nanofibers and amberlyst-15 particles exhibits stronger photoluminescence than the unblended areas because of the formed strong hydrogen bonding between. Furthermore, the interfacial adhesion between 1 nanofibers and amberlyst-15 particles can be amplified by H₂O₂, which in turn gives rise to rapid and remarkable fluorescence enhancement. When exposed to TATP vapors, the amberlyst-15 component can rapidly decompose TATP into H₂O₂ that gives sensitive fluorescence enhancement responses of the blend. On the basis of this detection mechanism, fluorescence detection of TATP with rapid response (ca. 5 s) and high sensitivity (ca. 0.1 ppm) is achieved. Here, the resulting blend combines the pretreatment of TATP and detection responses and thereby simplifies the senor fabrication for the practical application.