Comprehensive Analysis of Analogues of Amine-Related Psychoactive Substances Using Femtosecond Laser Ionization Mass Spectrometry

Abstract

Amine-related psychoactive molecules contain N–Cα and Cα–Cβ bonds, which easily dissociate to form various fragment ions in electron ionization mass spectrometry (EIMS). Therefore, observing a molecular ion and then determining the molecular weight of the analyte is difficult. In this study, we examined phenethylamine, 3,4-methylenedioxyphenethylamine, tryptamine, N-methylephedrine, and nicotine as well as analogues of amine-related psychoactive substances using EIMS and femtosecond laser ionization mass spectrometry (fs-LIMS) combined with gas chromatography for comprehensive analysis. A molecular ion was clearly observed in fs-LIMS for all of these compounds, which was in contrast to EIMS providing fragment ions dominantly (no molecular ion was observed for N-methylephedrine). This favorable result was obtained by adjusting the laser wavelength to the optimal value for two-photon ionization to minimize the excess energy remaining in the molecular ion. It therefore appears that fs-LIMS is superior to EIMS in terms of observing a molecular ion and would be potentially useful for identifying a variety of amine-related psychoactive substances, some of which are illegal and are of interest in the field of forensic science.

Determination of Barbiturates by Femtosecond Ionization Mass Spectrometry

“…This result suggests that barbiturates are very susceptible to undergoing photodissociation, probably due to the presence of carbonyl and amine groups and the low-frequency vibrational modes arising from flexible bulky groups in the side chain, which would accelerate the dissociation. As reported, the ratio decreases at shorter wavelengths with a gradual increase in excess energy by 2PI and decreases significantly at longer wavelengths with a substantial increase in excess energy by 3PI. , Note that RE2PI contributes more at shorter wavelengths for barbiturates (see Figures S2–S6). The optimal IE ( IE opt ), defined as the two-photon energy at the signal peak in Figure , and the excess energy (Δ E ), defined as the value of IE opt – IE , are summarized in Table .…”

“…These values were similar to those observed for very photodissociative compounds such as cis - and trans -4-methylcyclohexanols and psychoactive substances that contain amine groups, which were much smaller than the ca. 3 eV observed for ordinary organic compounds. ,, It is interesting to note that the M + /F + values observed for amobarbital and pentobarbital, which both contain only alkyl side chains, decreased more rapidly at longer wavelengths than those for butalbital and secobarbital with alkyl and alkenyl side chains. In addition, a molecular ion was observed only when Δ E was adjusted to be minimal for amobarbital (0.25 eV) and pentobarbital (0.27 eV) rather than for butalbital (0.56 eV) and secobarbital (0.56 eV).…”

“…As reported, the ratio decreases at shorter wavelengths with a gradual increase in excess energy by 2PI and decreases significantly at longer wavelengths with a substantial increase in excess energy by 3PI. 19,20 Note that RE2PI contributes more at shorter wavelengths for barbiturates (see Figures S2−S6). The optimal IE (IE opt ), defined as the two-photon energy at the signal peak in Figure 2, and the excess energy (ΔE), defined as the value of IE opt −IE, are summarized in Table 1.…”

“…In this case, the laser wavelength can be adjusted at half of the IE for 2PI, thus reducing the excess energy to zero. Based on this technique, molecular ions derived from organochlorine pesticides, 4-methylcyclohexanols, amine-related psychoactive substances, and even isotopes of small molecules such as N 2 have been observed. ,− Although the efficiency of NR2PI is generally lower than that of RE2PI, it approaches a level comparable to RE2PI when a laser pulse width of less than 100 fs is used . It is also noteworthy that photoionization dynamics and ionization efficiencies have been studied using femtosecond lasers. − …”