## 3 Results and Discussion  
The abbreviations of the 11 phenethylamine and 9 tryptamine standards (tabulated by structure) used in this study are shown in Table 1. In fact, 55 tryptamine and 179 phenethylamine compounds were synthesized and described by [PERSON] and [PERSON] in _TiHKAL_ and _PiHKAL_, respectively [13; 14]. These compounds have been abused since the mid-1980s. Hence, more detailed information about the characteristic mass fragments, produced under different types of ionization methods, is highly desirable for the screening and confirmation of phenethylamine and tryptamine derivatives. Figure 1a shows the basic structures of primary (1\({}^{\circ}\)), secondary (2\({}^{\circ}\)), and tertiary (3\({}^{\circ}\)) amines, respectively; the chemical structures of phenethylamine, tryptamine and their derivatives of various substituents are shown in Figure 1b. Figure 2 shows a general schematic outline for the \(\alpha\)-cleavage and \(\beta\)-cleavage based on ESI and MALDI modes, respectively, when \(N\),\(N\)-dimethyltryptamine (DMT; Mw: 188) was selected as the model compound. This scheme shows that, if a tryptamine (or phenethylamine) acquires a proton, it will form a [M+H]\({}^{+}\) ion. The \(\alpha\)-cleavage would progress at the \(C_{\alpha}\)-N bond, and, as a result, a cation (indole-containing group) and small neutral amine (NHR\({}_{\rm N1}\)R\({}_{\rm N2}\)) are formed. In this case, [M+H]\({}^{+}\) ion (\(m/z\): 189) and the cation (\(m/z\): 58) can be observed. However, the proton also could be donated to the \(C_{\beta}\) atom, leading to a \(C_{\alpha}\)-\(C_{\beta}\) bond breakage (i.e., \(\beta\)-cleavage). As a result, an iminium ion (CH\({}_{2}\)=N\({}^{+}\)R\({}_{\rm N1}\)R\({}_{\rm N2}\)) and a neutral fragment would form. Table 2 shows the differences and similarities in the mass spectra of these phenethylamine/tryptamine compounds when different ionization methods are applied, including EI-MS, ESI-MS and MALDI/TOFMS. It can be found that, in the case of ESI/MS, the ions of \(m/z=58\), 144 and 189 come from \(\beta\)-cleavage, \(\alpha\)-cleavage and [M+H]\({}^{+}\), respectively. In the case of MALDI/TOFMS, only \(\alpha\)-cleavage and [M+H]\({}^{+}\) can be found. In contrast, different fragments are found when EI mode was used. All of these characteristic peaks are very important to identify tryptamine and phenethylamine. Among these data, our group selected 2C-T-7 (a primary amine), 3_4_-MBDB (a secondary amine), and DET (a tertiary amine) as the model compounds for comparison, as described below. Figure 3 shows the EI/MS, ESI/MS and MALDI/TOFMS spectra of the three model compounds. As shown in Figure 3a (the upper mass spectrum; based on the EI mode), a parent ion of 2C-T-7, at \(m/z=255\), can be clearly observed. The other 2C series compounds also show similar consequences, as shown in Table 2, i.e., the parent ions obviously can be obtained. This is not a common phenomenon because, when the EI mode is used, in general, the energy of the electron makes it too difficult to obtain the parent ion. The reason for this could be that the functional groups (\(\mathrm{OCH_{3}}\) at R\({}_{3}\)/R\({}_{5}\) and halogens at R\({}_{4}\)) attach at the benzene ring, resulting in stronger C\({}_{\beta}\)-C\({}_{\alpha}\) and C\({}_{\alpha}\)-N bonds. In fact, the C\({}_{\alpha}\)-N bond does not break for any compound investigated in this study when the EI mode was used. Two fragment ions (\(m/z=30,225\)) clearly form because of the C\({}_{\beta}\)-C\({}_{\alpha}\) bond breakage; the C\({}_{\alpha}\)-N bond seems very difficult to break. The three characteristic peaks ([M]\({}^{+}\) and fragments from the C\({}_{\beta}\)-C\({}_{\alpha}\) bond breakage) are very unique and provide useful information for identifying 2C series compounds in actual forensic cases using the SIM (select ion monitoring) mode [12].