## 2 Results and Discussion
### Identification of Absorbed Constituents in Rabbit Plasma and CSF by HS-SPME-GC-MS
#### 2.2.2. Characterization of Eight Absorbed Lignans of AR by HPLC-APCI-IT-TOF-MS\({}^{n}\)
The UV spectrum of **L21** exhibited \(\lambda_{\rm max}\) at 263 nm, which implied that it was a 2,4-diene alkamide. The characteristic fragment ions at _m/z_ 201.1332 (C\({}_{14}\)H\({}_{17}\)O, [M+H-C\({}_{4}\)H\({}_{11}\)N]\({}^{+}\)), _m/z_ 175.1411 (C\({}_{13}\)H\({}_{19}\), [M+H-C\({}_{5}\)H\({}_{9}\)NO]\({}^{+}\)), and _m/z_ 173.1332 (C\({}_{13}\)H\({}_{17}\), [M+H-C\({}_{5}\)H\({}_{11}\)NO]\({}^{+}\)) in MS\({}^{2}\) spectra of **L21** indicated that it had the degree of unsaturation of 6 and an alkyl chain of 14 carbons, and it was _N_-isobutyl-tetradcapentaenamide. Therefore, **L21** was tentatively identified as _N_-isobutyl-2,4,8,10,12-tetradcapentaenamide. _Identification of **L22**_. It showed [M+H]\({}^{+}\) at _m/z_ 276.2322, which indicated that its molecular formula was C\({}_{18}\)H\({}_{29}\)NO. The UV spectrum of **L22** exhibited \(\lambda_{\rm max}\) at 262 nm, which indicated that it was a 2,4-diene alkamide. The characteristic fragment ions at _m/z_ 220.1623 (C\({}_{14}\)H\({}_{22}\)NO, [M+H-C\({}_{4}\)H\({}_{8}\)]\({}^{+}\)), _m/z_ 203.1457 (C\({}_{14}\)H\({}_{19}\)O, [M+H-C\({}_{4}\)H\({}_{11}\)N]\({}^{+}\)), _m/z_ 177.1611 (C\({}_{13}\)H\({}_{21}\), [M+H-C\({}_{5}\)H\({}_{9}\)NO]\({}^{+}\)), _m/z_ 175.1431 (C\({}_{13}\)H\({}_{19}\), [M+H-C\({}_{5}\)H\({}_{11}\)NO]\({}^{+}\)), _m/z_ 167.1297 (C\({}_{10}\)H\({}_{17}\)NO, [M+H-C\({}_{8}\)H\({}_{13}\)]\({}^{+}\)), _m/z_ 135.1181(C\({}_{10}\)H\({}_{15}\)), and _m/z_ 133.0970 (C\({}_{10}\)H\({}_{13}\)) in MS\({}^{2}\) spectra of **L22** indicated that it had the degree of unsaturation of 5 and an alkyl chain of 14 carbons, and it was _N_-isobutyl-tetradcactetraenamide. Accordingly, **L22** was tentatively identified as _N_-isobutyl-2,4,8,10-tetradcapentaenamide. _Identification of **L23**_. It showed [M+H]\({}^{+}\) at _m/z_ 252.2317, which indicated that its molecular formula was C\({}_{16}\)H\({}_{29}\)NO. The UV spectrum of **L23** exhibited \(\lambda_{\rm max}\) at 262 nm, which indicated that it was a 2,4-diene alkamide. The characteristic fragment ions at _m/z_ 196.1744 (C\({}_{12}\)H\({}_{22}\)NO, [M+H-C\({}_{4}\)H\({}_{8}\)]\({}^{+}\)), _m/z_ 179.1256 (C\({}_{12}\)H\({}_{9}\)O, [M+H-C\({}_{4}\)H\({}_{11}\)N]\({}^{+}\)), _m/z_ 154.1227 (C\({}_{9}\)H\({}_{16}\)NO, [M+H-C\({}_{7}\)H\({}_{14}\)]\({}^{+}\)), and _m/z_ 95.0480 (C\({}_{6}\)H\({}_{7}\)O) in MS\({}^{2}\) spectra of **L23** indicated that it had the degree of unsaturation of 3 and an alkyl chain of 12 carbons, and it was _N_-isobutyl-2,4-dodecaenamide. Accordingly, **L23** was tentatively identified as _N_-isobutyl-2,4-dodecaenamide. _Identification of **L13**_. It showed [M+H]\({}^{+}\) at _m/z_ 222.1842, which indicated that its molecular formula was C\({}_{14}\)H\({}_{23}\)NO. The characteristic fragment ions at _m/z_ 167.1237 (C\({}_{10}\)H\({}_{17}\)NO, [M+H-C\({}_{4}\)H\({}_{7}\)]\({}^{+}\)), _m/z_ 166.1329 (C\({}_{10}\)H\({}_{16}\)NO, [M+H-C\({}_{4}\)H\({}_{8}\)]\({}^{+}\)), _m/z_ 152.0970 (C\({}_{9}\)H\({}_{14}\)NO, [M+H-C\({}_{5}\)H\({}_{10}\)]\({}^{+}\)), _m/z_ 149.0985 (C\({}_{10}\)H\({}_{13}\)O, [M+H-C\({}_{4}\)H\({}_{11}\)N]\({}^{+}\)), and _m/z_ 81.0807(C\({}_{6}\)H\({}_{9}\), [M+H-C\({}_{8}\)H\({}_{15}\)NO]\({}^{+}\)) in MS\({}^{2}\) spectra of **L13** indicated that it had the degree of unsaturation of 4 and an alkyl chain of 10 carbons. According to literature [18], **L13** was tentatively identified as spilanthol, _i.e._, _N_-isobutyl-2_,6_,8_E_-decatrienamide, which was isolated from the roots and rhizomes of _Asarum longerhizomomatosum_[23]. .2.4. Characterization of FourAbsorbed Phenylpropanoloids of AR by HPLC-APCI-IT-TOF-MS\({}^{\rm n}\)  
_Identification of **L9** and **L11**_. **L9** and **L11** were confirmed to be kakuol methyl ether and kakuol by comparing their retention times and MS\({}^{\rm n}\) data with those of the reference compounds. _Identification of **L4**_. It showed [M+H]\({}^{+}\) at _m/z_ 211.0955, indicating the molecular formula of C\({}_{11}\)H\({}_{14}\)O\({}_{4}\).