初级芳香胺的高分辨质谱裂解规律研究

为探究初级芳香胺类化合物的质谱裂解规律,本研究采用超高效液相色谱-四极杆/静电场轨道阱高分辨质谱法,在电喷雾正离子模式下采集数据,根据一、二级质谱离子的精确质荷比推导14种初级芳香胺类化合物可能的裂解途径。结果表明,由于分子结构中存在氨基基团,因此初级芳香胺类化合物极易被质子化,更易形成M+H]⁺。断裂过程主要发生NH₃中性碎片的丢失,产生M+H-NH₃]⁺特征碎片离子,在此基础上,氯代苯胺类化合物发生碳正离子重排后,丢失氯原子形成·M+H-NH₃-Cl]⁺碎片离子。甲氧基取代苯胺类化合物可丢失CH₃O基团产生碎片离子M+H-NH₃-CH₃O]⁺,或发生碳正离子转移重排至苯甲基,进一步丢失CH₃和CH₃O基团。甲基或甲氧基取代的联苯胺类化合物还会发生CN键断裂形成M+H-NH]⁺,继而丢失NH₃中性碎片形成M+H-NH-NH₃]⁺。偶氮苯类化合物中高键能的偶氮键不易断裂,碎片离子主要通过两侧的CN键断裂形成。本研究提出的最佳电离方式和质谱裂解规律为初级芳香胺类化合物的快速鉴定提供了重要依据。

The High-Resolution Mass Spectral Fragmentation Pathways of Primary Aromatic Amines

To study the mass spectral fragmentation pathways of primary aromatic amines by ultra-performance liquid chromatography coupled to quadrupole orbitrap high-resolution mass spectrometry. The data was collected under electrospray negative ion mode, and the fragmentation pathways of 14 primary aromatic amines were derived by the precise mass-to-charge ratio of the first and second mass spectrometry ions. The results showed that the existence of amino groups in molecular structure could easily be protonated to form M+H]⁺, and the cracking process mainly lost the neutral molecule NH₃ and produced M+H-NH₃]⁺. After that, the chlorinated anilines underwent carbocation rearrangement and then lost the chlorine atoms, resulting in characteristic fragment ion ·M+H-NH₃-Cl]⁺. Methoxy substituted anilines lost the CH₃O group and produced M+H-NH₃-CH₃O]⁺, or carbocation transferred and rearranged to benzyl, further losing CH₃ and CH₃O groups. Methyl or methoxy substituted benzidine compounds also can undergo CN bond cleavage to form M+H-NH]⁺, and then lost the neutral molecule NH₃ to produce M+H-NH-NH₃]⁺. Azobenzene compounds are not easy to break the azo bond with high bond energy, and the fragment ions are mainly formed by breaking the CN bonds on both sides. The best ionization mode and mass spectral fragmentation pathways proposed in this study provides an important basis for the rapid identification and analysis of such primary aromatic amines.