RESUMO
The laser desorption/laser ionization time-of-flight (L2ToF), mass spectra of anthracene and the anthracene-picric acid charge transfer (C-T) complex have been compared at a desorption and ionization wavelength of 266 nm. Laser desorption/ionization spectra of anthracene were obtained at low temperatures (-30 °C) to minimize the interference from gas phase ionization. Positive ion mass spectra of the picrate C-T complex at room temperature comprise the parent ion of anthracene and were devoid of signals associated with the picric acid component. The L2ToF analyses of a mixture of volatile and involatile EPA priority PAHs in picric acid show that low molecular weight PAHs form involatile charge transfer complexes. The present method reduces the possibility of volatile PAH loss during mass spectrometric analyses in vacuo.
RESUMO
Femtosecond laser time-of-flight mass spectra of solid samples of trinitrobenzene (TNB), trinitrotoluene (TNT) and trinitrophenol (TNP) have been recorded. Desorption of the solid samples was enacted by the fourth harmonic output (266 nm) of a 5 ns Nd:YAG laser. Subsequent femtosecond post-ionisation of the plume of neutral molecules was achieved using 800 nm laser pulses of 80 fs duration. Mass spectra have been recorded for desorption laser intensities from 2-6 x 10(9) W cm(-2) with ionisation laser intensities between 2 x 10(14) and 6 x 10(15) W cm(-2). Femtosecond laser ionisation has been shown to be capable of generating precursor and characteristic high-mass fragment ions for labile nitro-aromatic molecules commonly used in high-explosive materials. This feature is critical in the future development of femtosecond laser-based analytical instruments that can be used for complex molecular identification and quantitative analysis of environmentally important labile molecules. Furthermore, a comparison of femtosecond post-ionisation mass spectra with standard 70 eV electron impact data has revealed similarities in the spectra and hence the fragmentation processes.