## 2 Results and Discussion
### Identification of Absorbed Constituents in Rabbit Plasma and CSF by HS-SPME-GC-MS
#### 2.2.1. Fragmentation Behaviors of Four Reference Compounds in APCI-MS\({}^{\mathrm{n}}\)  
_Fragmentation behavior of l-asarinin (molecular formula: C\({}_{20}\)H\({}_{18}\)O\({}_{6}\); exact mass: 354.1103)._ The quasi-molecular ion [M+H]\({}^{+}\) of _l_-asarinin was observed at _m/z_ 355.1178, and the base peak ion [M+H-H\({}_{2}\)O]\({}^{+}\) at _m/z_ 337.1045 was observed in MS spectrum. In MS\({}^{2}\) spectrum, the precursor ion [M+H-H\({}_{2}\)O]\({}^{+}\) at _m/z_ 337.1045 (C\({}_{20}\)H\({}_{17}\)O\({}_{5}\)) fragmented into product ions at _m/z_ 319.0955 (C\({}_{20}\)H\({}_{15}\)O\({}_{4}\), [M+H-2H\({}_{2}\)O]\({}^{+}\)), _m/z_ 289.0846 (C\({}_{19}\)H\({}_{13}\)O\({}_{3}\), [M+H-2H\({}_{2}\)O-CH\({}_{2}\)O]\({}^{+}\)), _m/z_ 261.0901 (C\({}_{18}\)H\({}_{13}\)O\({}_{2}\), [M+H-2H\({}_{2}\)O-CH\({}_{2}\)O-CO]\({}^{+}\)), _m/z_ 231.0803 (C\({}_{17}\)H\({}_{11}\)O, [M+H-2H\({}_{2}\)O-CH\({}_{2}\)O-CO-CH\({}_{2}\)O]\({}^{+}\)), _m/z_ 203.0885 (C\({}_{16}\)H\({}_{11}\), [M+H-2H\({}_{2}\)O-CH\({}_{2}\)O-CO-CH\({}_{2}\)O-CO]\({}^{+}\)), and _m/z_ 135.0434 [C\({}_{8}\)H\({}_{7}\)O\({}_{2}\)]\({}^{+}\). The ion at _m/z_ 135.0434 [C\({}_{8}\)H\({}_{7}\)O\({}_{2}\)]\({}^{+}\) is a very important characteristic fragment ion for identifying the structure of the aryl group in furofuran lignans, which indicated that the aryl group was 3,4-methylenedioxyphenyl [13, 14]. Figure 6: Chemical structures of 23 absorbed constituents identified in rabbit plasma from AR EtOAc extract group identified by HPLC-APCI-IT-TOF-MS\({}^{\mathrm{n}}\). In the MS\({}^{3}\) spectrum, the precursor ion [M+H-2H\({}_{2}\)O-CH\({}_{2}\)O]\({}^{+}\) at _m/z_ 289.0846 further fragmented into product ions at _m/z_ 261.0929 (C\({}_{18}\)H\({}_{13}\)O\({}_{2}\), [M+H-2H\({}_{2}\)O-CH\({}_{2}\)O-CO]\({}^{+}\)), _m/z_ 231.0795 (C\({}_{17}\)H\({}_{11}\)O, [M+H-2H\({}_{2}\)O-CH\({}_{2}\)O-CO-CH\({}_{2}\)O]\({}^{+}\)), and _m/z_ 203.0864 (C\({}_{16}\)H\({}_{11}\), [M+H-2H\({}_{2}\)O-CH\({}_{2}\)O-CO-CH\({}_{2}\)O-CO]\({}^{+}\)). _Fragmentation behavior of epipinoresinol (molecular formula: C\({}_{20}\)H\({}_{22}\)O\({}_{6}\); exact mass: 358.1416)._ In MS spectrum, the quasi-molecular ion [M+H]\({}^{+}\) of epipinoresinol was observed at _m/z_ 359.1444, and the base peak ion [M+H-H\({}_{2}\)O]\({}^{+}\) at _m/z_ 341.1363 (C\({}_{20}\)H\({}_{21}\)O\({}_{5}\)) was observed. In the MS\({}^{2}\) spectrum, the precursor ion [M+H-H\({}_{2}\)O]\({}^{+}\) at _m/z_ 341.1363 (C\({}_{20}\)H\({}_{21}\)O\({}_{5}\)) fragmented into product ions at _m/z_ 323.1258 (C\({}_{20}\)H\({}_{19}\)O\({}_{4}\), [M+H-2H\({}_{2}\)O]\({}^{+}\)), _m/z_ 291.0994 (C\({}_{19}\)H\({}_{15}\)O\({}_{3}\), [M+H-2H\({}_{2}\)O-CH\({}_{3}\)OH]\({}^{+}\)), _m/z_ 263.1042 (C\({}_{18}\)H\({}_{15}\)O\({}_{2}\), [M+H-2H\({}_{2}\)O-CH\({}_{3}\)OH-CO]\({}^{+}\)), _m/z_ 259.0734 (C\({}_{18}\)H\({}_{11}\)O\({}_{2}\), [M+H-2H\({}_{2}\)O-2 CH\({}_{3}\)OH]\({}^{+}\)), and _m/z_ 137.0596 ([C\({}_{8}\)H\({}_{9}\)O\({}_{2}\)]\({}^{+}\)). The successive losses of two CH\({}_{3}\)OH from the ion _m/z_ 323.1258 indicated that there were two _o_-methoxy hydroxyphenyls in the structure, and the characteristic ion at _m/z_ 137.0596 ([C\({}_{8}\)H\({}_{9}\)O\({}_{2}\)]\({}^{+}\)) further confirmed this. In MS\({}^{3}\) spectrum, the precursor ion [M+H-2H\({}_{2}\)O]\({}^{+}\) at _m/z_ 323.1186 generated product ions at _m/z_ 291.1024 [M+H-2H\({}_{2}\)O-CH\({}_{3}\)OH]\({}^{+}\) and _m/z_ 263.1052 [M+H-2H\({}_{2}\)O-CH\({}_{3}\)OH-CO]\({}^{+}\); the precursor ion at _m/z_ 291.0094 (C\({}_{19}\)H\({}_{15}\)O\({}_{3}\)) gave product ions at _m/z_ 276.0793 (C\({}_{18}\)H\({}_{12}\)O\({}_{3}\)) by losing a methyl radical, which also indicated that there was a methoxyl group in the molecule. _Fragmentation behavior of kakuol (molecular formula: C\({}_{10}\)H\({}_{10}\)O\({}_{4}\); exact mass: 194.0579)._ In MS spectrum, kakuol showed quasi-molecular ion [M+H]\({}^{+}\) at _m/z_ 195.0648.