## 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\({}^{n}\)
**L14** was an isomer of **L15**, which showed [M+H]\({}^{+}\) at _m/z_ 355.12 and the base peak ion [M+H-H\({}_{2}\)O]\({}^{+}\) at _m/z_ 337.10 in MS. The MS\({}^{2}\) of **L15** showed characteristic product ions at _m/z_ 289.08 (C\({}_{19}\)H\({}_{13}\)O\({}_{3}\), [M+H-2H\({}_{2}\)O-CH\({}_{2}\)O]\({}^{+}\)) and _m/z_ 135.0434 [C\({}_{8}\)H\({}_{7}\)O\({}_{2}\)]\({}^{+}\), which was consistent with that of _l_-sesamin [15], so **L15** was tentatively identified as _l_-sesamin. 2.3 Characterization of Nine Absorbed N-alkylamides of AR by HPLC-APCI-IT-TOF-MS\({}^{\text{n}}\)  
The nine absorbed constituents (**L13**, **L16**-**L23**) were identified as _N_-isobutylamides, because of their characteristic neutral losses of 56 Da (C\({}_{4}\)H\({}_{8}\)), 73 Da (C\({}_{4}\)H\({}_{11}\)N), 99 Da (C\({}_{5}\)H\({}_{9}\)NO) and 101 Da (C\({}_{5}\)H\({}_{11}\)NO) from _N_-isobutylamide were observed in their MS\({}^{\text{n}}\) spectra [18; 19; 20; 21]. _Identification of **L16**-**L19**_. All of them showed [M+H]\({}^{+}\) at _m/z_ 248.20, which indicated that their molecular formulae were C\({}_{16}\)H\({}_{25}\)NO. The fragment ions at _m/z_ 192.14 (C\({}_{12}\)H\({}_{18}\)NO, [M+H-C\({}_{4}\)H\({}_{8}\)]\({}^{+}\)), _m/z_ 175.11 (C\({}_{12}\)H\({}_{15}\)O, [M+H-C\({}_{4}\)H\({}_{11}\)N]\({}^{+}\)), _m/z_ 167.13 (C\({}_{10}\)H\({}_{17}\)NO, [M+H-C\({}_{6}\)H\({}_{9}\)]\({}^{+}\)), _m/z_ 166.12 (C\({}_{10}\)H\({}_{16}\)NO, [M+H-C\({}_{6}\)H\({}_{10}\)]\({}^{+}\)), _m/z_ 149.13 (C\({}_{11}\)H\({}_{17}\), [M+H-C\({}_{5}\)H\({}_{9}\)NO]\({}^{+}\)), _m/z_ 147.12 (C\({}_{11}\)H\({}_{15}\), [M+H-C\({}_{5}\)H\({}_{11}\)NO]\({}^{+}\)), _m/z_ 133.07 (C\({}_{9}\)H\({}_{9}\)O, [M+H-C\({}_{4}\)H\({}_{11}\)N-C\({}_{3}\)H\({}_{6}\)]\({}^{+}\)), _m/z_ 121.10 (C\({}_{9}\)H\({}_{13}\), [M+H-C\({}_{7}\)H\({}_{13}\)NO]\({}^{+}\)), and _m/z_ 107.08 (C\({}_{8}\)H\({}_{11}\), [M+H-C\({}_{7}\)H\({}_{13}\)NO]\({}^{+}\)) were observed in their MS\({}^{2}\) spectra, which indicated that they had the degree of unsaturation of 5 and an alkyl chain of 12 carbons, and they were _N_-isobutyl-2,4,8,10-dodecateraenamides [19]. Their UV spectra exhibited \(\lambda_{\text{max}}\) at 259 nm, which further confirmed that they were 2,4-diene alkamides. Besides, the peak areas of **L16** and **L17** were bigger than those of **L18** and **L19**, indicating that **L16** and **L17** were more abundant than **L18** and **L19**. Because _N_-isobutyl-2\(E\),4\(E\),8\(Z\),10_E_-dodecateraenamide and _N_-isobutyl-2\(E\),4\(E\),8\(Z\),10_Z_-dodecateraenamide were isolated from Asari Radix et Rhiz [22], and the _2\(E\),4\(E\),8\(Z\),10_Z_-isomer elite before _2\(E\),4\(E\),8\(Z\),10_E_-isomer in HPLC [20], **L16** was tentatively identified as _N_-isobutyl-2\(E\),4\(E\),8Z_,10_Z_-dodecateraenamide and **L17** as _N_-isobutyl-2\(E\),4\(E\),8Z_,10_E_-dodecateraenamide. Besides, **L18** and **L19** were tentatively identified as _N_-isobutyl-2,4,8,10-dodecateraenamide isomers. _Identification of **L20**_. It showed [M+H]\({}^{+}\) at _m/z_ 250.2150, indicating the molecular formula of C\({}_{16}\)H\({}_{27}\)NO. Its UV spectrum exhibited \(\lambda_{\text{max}}\) at 262 nm, which indicated that **L20** was a 2,4-diene alkamide. The fragment ions at _m/z_ 194.1625 (C\({}_{12}\)H\({}_{20}\)NO, [M+H-C\({}_{4}\)H\({}_{8}\)]\({}^{+}\)), _m/z_ 177.1164 (C\({}_{12}\)H\({}_{17}\)O, [M+H-C\({}_{4}\)H\({}_{11}\)N]\({}^{+}\)), _m/z_ 167.1302 (C\({}_{10}\)H\({}_{17}\)NO, [M+H-C\({}_{6}\)H\({}_{11}\)]\({}^{+}\)), _m/z_ 152.1070 (C\({}_{9}\)H\({}_{14}\)NO, [M+H-C\({}_{7}\)H\({}_{14}\)]\({}^{+}\)), and _m/z_ 149.1398 (C\({}_{11}\)H\({}_{17}\), [M+H-C\({}_{5}\)H\({}_{11}\)NO]\({}^{+}\)) in MS\({}^{2}\) of **L20** indicated that it had the degree of unsaturation of 4 and an alkyl chain of 12 carbons, and it was _N_-isobutyl-dodecatrienamide. By comparison with the literature [20], **L20** was tentatively identified as _N_-isobutyl-2,4,8-dodecatrienamide. _Identification of **L21**_. It showed [M+H]\({}^{+}\) at _m/z_ 274.2164, indicating the molecular formula of C\({}_{18}\)H\({}_{27}\)NO.