Multiphoton ionization mass spectrometry of nitrated polycyclic aromatic hydrocarbons

Analysis of Parent/Nitrated Polycyclic Aromatic Hydrocarbons in Particulate Matter 2.5 Based on Femtosecond Ionization Mass Spectrometry

“…In the present study, a UV femtosecond laser emitting at 267 nm was utilized as the ionization laser, which corresponds to 4.64 eV as a photon energy. On the other hand, the ionization energy was estimated to be 7.5-8.0 eV for NPAHs based on quantum chemical calculations as shown in Figure 3, which was not significantly changed from the data calculated using a different basis set [26]. Assuming that the NPAHs are ionized through a two-photon process, the excess energy is calculated to be 1.2-1.7 eV.…”

“…The procedure has been reported elsewhere and is briefly described here [25]. In the previous study, the optimized geometry of the ground state and the energies of the ground and ion states were evaluated using B3LYP at the level of cc-pVTZ basis sets [26]. In this study, the data were calculated at a level of cc-pVDZ basis set for comparison.…”

“…It is, however, rather difficult to decrease the excess energy by changing the laser wavelength. The other approach is the use of a laser emitting at longer wavelengths for resonanceenhanced two-photon ionization, which is achievable at a wavelength of 300-400 nm [26]. Figure 4 shows expanded views of a two-dimensional display measured for a sample extracted from PM2.5.…”

“…Accordingly, improving the sensitivity of the analytical instrument by two orders of magnitude would be highly desirable. Such an improvement could be achieved by increasing the size of the filter used for extraction (e.g., 1.5 cm 2 → 401 cm 2 ) 225 27 26 and by concentrating the sample solution (e.g., 1 mL → 20 μL) before it is injected into the GC: it was difficult to demonstrate this in the present study because of a limited amount of the PM2.5 sample, since the major part of the sample was used in the study of PAHs and additional sampling of PM2.5 for the study of NPAHs can only be performed on the day providing a high level of PM2.5 that is exceptional in Japan. It should be noted that a high-power laser with a higher repetition rate (e.g., 20 kHz) would be a distinct advantage in terms of improving the sensitivity of the analysis.…”

Resonant and non-resonant femtosecond ionization mass spectrometry of organochlorine pesticides

“…30 However, it should be noted that the background signal from interference also increases when a laser emitting at shorter wavelengths is used. 34,35 Therefore, further optimization will be needed for this to be used in actual trace analysis.…”