## 2 Results and Discussion
### LC-ESI--LTQ-MS\({}^{n}\) Cannabinoids Identification
A similar scenario applies to the acid precursor THCA, as well as CBDA, showed a poor informative MS/MS fragmentation spectrum in negative mode (Table 2). However, [PERSON] et al. [24] establish the basis for thorough discrimination between THCA and CBDA, detected as deprotonated ions ([M \(-\) H]\({}^{-}\): C\({}_{22}\)H\({}_{29}\)O\({}_{4}\)\({}^{-}\)) at \(m/z\) 357, leading to an appropriate chemical characterization guideline. Firstly, the discrimination between THCA and CBDA was based on the MS/MS fragments they share, e.g., fragment ions due to dehydration; ([M \(-\) H\(-\)H\({}_{2}\)O]\({}^{-}\) at \(m/z\) 339) and decarboxylation ([M \(-\) H\(-\)CO\({}_{2}\)]\({}^{-}\) at \(m/z\) 313): the [M \(-\) H\(-\)CO\({}_{2}\)]\({}^{-}\)/[M \(-\) H\(-\)H\({}_{2}\)O]\({}^{-}\) abundance ratio resulted \(<\) 1 in CBDA and \(>\) 1 in THCA, as already reported in literature [24]. Additionally, ions at \(m/z\) 227 and 271 are present only in the MS\({}^{3}\) spectrum of CBDA. The first one could be attribuited to a neutral loss of of 44 Da and 18 Da alongside an isoprenic unit (\(-\)68 Da) from the precursor ion, while the second one was lately referred to as the product of a retro Diels-Alder (RDA) reaction, involving the [M \(-\) H\(-\)H\({}_{2}\)O]\({}^{-}\) ion at \(m/z\) 339 [23]. Instead, in the MS\({}^{3}\) spectrum of THCA, the RDA occurrence produced the ion at \(m/z\) 245 (2,-dimethyl-7-pentyl-2H-chromen-5-olate), which promptly retro-cyclized to get the ion at \(m/z\) 191 [24]. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Compound**} & **Molecular Formula as** & **Nominal \(m/z\) Value** & **CID MS/MS and** \\  & **[M \(+\) H]\({}^{+}\)/[M \(-\) H]\({}^{-}\)** & **[M \(+\) H]\({}^{+}\)/[M \(-\) H]\({}^{-}\)** & **Med Ross (\(m/z\)) a** \\  & **[M \(+\) H]\({}^{+}\)/[M \(-\) H]\({}^{-}\)** & **Med Ross Error** \\  & & & **(ppm)** \\ \hline \hline THC & & & \\ \(\mathrm{OH}\) & C\({}_{21}\)H\({}_{31}\)O\({}_{2}\)\({}^{+}\) & 315 & 111 (0.54); 123 (0.37); 135 (0.44); 175 (MS\({}^{4}\)); 181 (0.81); 193 (0.016); 207 (0.60); 227 (MS\({}^{3}\)); 231 (MS\({}^{3}\)); 233 (0.14); 235 (0.85); 245 (0.13); 259 (0.14); 273 (1.03); 297 (0.31) & \\ \hline THCA & & & \\ \(\mathrm{OH}\) & C\({}_{22}\)H\({}_{29}\)O\({}_{4}\)\({}^{-}\) & 357 & 191 (MS\({}^{3}\)); 245 (MS\({}^{3}\)); 313; 339 & \\ \hline CBDA & & & \\ \(\mathrm{OH}\) & C\({}_{22}\)H\({}_{29}\)O\({}_{4}\)\({}^{-}\) & 357 & 227 (MS\({}^{3}\)); 271 (MS\({}^{3}\)); 313; 339 & \\ \hline CBN & & & \\ \(\mathrm{OH}\) & C\({}_{21}\)H\({}_{27}\)O\({}_{2}\)\({}^{+}\) & 311 & 195 (MS\({}^{4}\)); 223 (MS\({}^{3}\)); 241; 265; 293 & \\ \hline \hline \end{tabular} \({}^{a}\)Mass error was expressed in parts per million of five \(m/z\) measurements.  
\end{table} 
Table 2: Cannabinoids occurring in a sample of light _Camabis sativa_ extract underststudy, identified as intact protonated molecules, [M \(+\) H]\({}^{+}\) for THC, CBD, and CBN, and intact deprotonated molecules, [M \(-\) H]\({}^{-}\), for THCA and CBDA, by using LC-ESI-LTQ MS\({}^{n}\) and collision-induced dissociation (CID) as a fragmentation technique. Finally, CBN was identified as a protonated ion ([M + H]\({}^{+}\): C\({}_{21}\)H\({}_{27}\)O\({}_{2}\)\({}^{+}\)) at \(m/z\) 311. It fragmented differently (Table 2) than other cannabinoids because of the stability of the aromatic ring [6]. The base peak at \(m/z\) 293 was related to water loss. The ions at \(m/z\) 223 and 195 detected in the CID MS\({}^{3}\) and CID MS\({}^{4}\) spectra, respectively, suggest that the fragment ions produced are the result of consecutive leakages of the pentyl side chain and two methyl groups of [M \(-\) H\(-\)H\({}_{2}\)O]\({}^{-}\) ion at \(m/z\) 293. The benzopyran ring opening of CBN resulted in the diagnostic fragment ion at \(m/z\) 265. A fragment ion with higher signal intensity was observed at \(m/z\) 241 and it is attribuible to the cleavage of the aliphatic 5-carbon chain from the precursor ion.