Ultrashort Pulse Photoionization for Femtosecond Laser Mass Spectrometry

Experimental and Theoretical Analysis of Tricyclic Antidepressants by Ultraviolet Picosecond Laser Desorption Post-Ionization Mass Spectrometry

“…Both the m/z 86 and 194 fragment ions are also observed in fs-LDPI-MS of imipramine using 800 nm photons for desorption. 34 Similar BDE values are obtained for the analogous fragmentation pathways in clomipramine and desipramine, while substantially higher BDEs are obtained for the fragmentation pathways forming 72 and 85 amu in amitriptyline due to the presence of the carbon−carbon double bond (see Supporting. Information Figure S7).…”

“…The lowest-energy pathway (BDE = 2.21 eV) leading to 194 + 86 amu is consistent with the m / z 86 fragment ion being the most intense of the small amine ions and the intense m / z 194 fragment observed in Figure . Both the m / z 86 and 194 fragment ions are also observed in fs-LDPI-MS of imipramine using 800 nm photons for desorption . Similar BDE values are obtained for the analogous fragmentation pathways in clomipramine and desipramine, while substantially higher BDEs are obtained for the fragmentation pathways forming 72 and 85 amu in amitriptyline due to the presence of the carbon–carbon double bond (see Supporting.…”

“…Dissociation during laser desorption has been previously observed. , The electronic structure calculations found that some of the neutral fragments were stabilized by a hydrogen atom rearrangement. The mechanism of single-photon ionization and any associated fragmentation can be readily supported by electronic structure calculations …”

“…By contrast, the ∼10 8 W/cm 2 desorption laser fluence used in the 213 nm ps-LDPI experiments is firmly in the range of traditional resonant multiphoton ionization. 34 These drastically different laser fluences imply different initiating photoionization processes for desorption by picosecond vs femtosecond laser pulses. While the picosecond time scale of electron−lattice heating 10 puts ∼30 ps-LD at the threshold of the reduced vibrational energy transfer that occurs in fs-LD, ps-LD may nevertheless proceed at least in part by a thermal mechanism that is unlikely for fs-LD.…”

Laser-Pulse-Length Effects in Ultrafast Laser Desorption

“…For the matrix-free LD with postionization, a number of studies indicate benefits of ultrashort fs- and ps-lasers, e.g., with respect to the aforementioned parameters, softness − and efficiency. , Also, thermal damage to the substrate, e.g., tissue, is reduced for fs-desorption − as well as matrix effects . Beyond LD, laser-pulse-length effects have been investigated for LDI and MALDI. − …”