Arnould Mark A, Buehner Rita W, Wesdemiotis Chrys, Vargas Rafael
Department of Chemistry, The University of Akron, Akron, Ohio 44325-3601, USA.
Eur J Mass Spectrom (Chichester). 2005;11(2):243-56. doi: 10.1255/ejms.746.
Electrospray ionization of polyesters composed of isophthalic acid and neopentyl glycol produces carboxylate anions in negative mode and mainly sodium ion adducts in positive mode. A tandem mass spectrometry (MS/MS) study of these ions in a quadrupole ion trap shows that the collisionally activated dissociation pathways of the anions are simpler than those of the corresponding cations. Charge-remote fragmentations predominate in both cases, but the spectra obtained in negative mode are devoid of the complicating cation exchange observed in positive mode. MS/MS of the Na(+) adducts gives rise to a greater number of fragments but not necessarily more structural information. In either positive or negative mode, polyester oligomers with different end groups fragment by similar mechanisms. The observed fragments are consistent with rearrangements initiated by the end groups. Single-stage ESI mass spectra also are more complex in positive mode because of extensive H/Na substitutions; this is also true for matrix-assisted laser desorption ionization (MALDI) mass spectra. Hence, formation and analysis of anions might be the method of choice for determining block length, end group structure and copolymer sequence, provided the polyester contains at least one carboxylic acid end group that is ionizable to anions.
由间苯二甲酸和新戊二醇组成的聚酯在负离子模式下进行电喷雾电离会产生羧酸根阴离子，在正离子模式下主要产生钠离子加合物。在四极杆离子阱中对这些离子进行串联质谱（MS/MS）研究表明，阴离子的碰撞激活解离途径比相应阳离子的更简单。在两种情况下，电荷远程碎裂都占主导，但负离子模式下获得的谱图没有正离子模式中观察到的复杂阳离子交换现象。钠离子加合物的MS/MS产生更多碎片，但不一定能提供更多结构信息。在正离子或负离子模式下，具有不同端基的聚酯低聚物通过类似机制碎裂。观察到的碎片与由端基引发的重排一致。由于广泛的氢/钠取代，单级电喷雾电离质谱在正离子模式下也更复杂；基质辅助激光解吸电离（MALDI）质谱也是如此。因此，只要聚酯含有至少一个可电离为阴离子的羧酸端基，阴离子的形成和分析可能是确定嵌段长度、端基结构和共聚物序列的首选方法。
