亚胺化结合气相色谱-质谱法区分二氨基甲苯异构体

Differentiation of Isomeric Diamintoluenes by Imidization and Gas Chromatography-Mass Spectrometry

2,4-二氨基甲苯是食品包装材料中禁用的致癌芳香胺,区分2,4-二氨基甲苯及其异构体具有较大的挑战性。本研究采用苯甲醛进行二氨基甲苯异构体的亚胺化反应,气相色谱-质谱法分析5种二氨基甲苯异构体的亚胺化产物。同时,采用理论计算探索2,3-二氨基甲苯亚胺化产物的质谱碎裂机理。邻位二氨基甲苯与苯甲醛反应生成1-苄基-2-苯基-甲基苯并咪唑类和2-苯基-甲基苯并咪唑,非邻位二氨基甲苯与苯甲醛反应则生成亚胺类产物。所有的衍生物易实现气相色谱分离;由于邻基效应等因素,5个二氨基甲苯异构体的亚胺化产物可实现EI质谱区分。研究结果表明,亚胺化有助于同时精准测定二氨基甲苯同分异构体。

Accurate determination of 2,4-diaminotoluene is of great significance due to its carcinogenic effect and its common existence in food packaging materials.However,2,4-diaminotoluene shares similar EI-MS behavior with its isomers,and it is difficult to separate 2,4-diaminoto-luene with its isomers on many common chromatographic column.Thus,it is a great challenge for differentiation of carcinogenic 2,4-diaminotoluene with its isomers.In this work,imidization of 5 commercial available diaminotoluenes with benzaldehyde was carried out,and the products were analyzed by gas chromatography-mass spectrometry.Both of the two nonadjacent amino groups in m-or p-diaminotoluene underwent imidization with benzaldehyde,respectively,while derivatization of o-diaminotoluene resulted in 1-benzyl-2-phenyl-methyl-1H-benzo[d]imidazole and 2-phenyl-methyl-1H-benzo[d]imidazole at room temperature,while only led to 2-phenyl-methyl-1H-benzo[d]imidazole when heated.All of the derivatives were easily separated on a common HP-5MS capillary column.They underwent the loss of H atom or phenyl radical in EI-MS.Due to the ortho-effect,from 2,3-diaminotoluene underwent dissociation to give a characteristic product ion at m/z 207,and thus they can be differentiated from 3,4-diaminotoluene.Both of the imino groups in the derivative of 2,4-diaminotoluene participated in the fragmentation reaction,which resulted in characteristic product ions at m/z 207 and m/z 195.Both of the imino groups were in the conjugated position in the derivative of 2,5-diaminotoluene,and thus the molecular ion was especially stable with much high abundance.Thus,all of these derivatives were recognized by EI-MS.Theoretical calculations at the B3LYP/6-31G(d)level were carried out to probe the EI-MS fragmentation of the imidization product of the 2,3-diaminotoluene,in which migration of one of the methyl H atoms to the neighboring N atom led to the loss of the benzyl radical.The results provide a promising solution for simultaneous determination of diaminotoluene isomers.