Adriaensen L, Vangaever F, Lenaerts J, Gijbels R
Department of Chemistry (MiTAC), University of Antwerp, Wilrijk, Belgium.
J Mass Spectrom. 2005 May;40(5):615-27. doi: 10.1002/jms.832.
A series of cationic, zwitterionic and anionic fluorinated carbocyanine dyes, spin-coated on Si substrates, were measured with time-of-flight static secondary ion mass spectrometry (TOF-S-SIMS) under Ga(+) primary ion bombardment. Detailed fragmentation patterns were developed for all dyes measured. In the positive mode, the resulting spectra showed very intense signals for the precursor ions of the cationic dyes, whereas the protonated signals of the anionic dyes were hardly detected. Differences of three orders of magnitude were repeatedly observed for the secondary ion signal intensities of cationic and anionic dyes, respectively. All measured dyes yielded mass spectra containing several characteristic fragment ions. Although the secondary ion yields were still higher for the cationic than the anionic dye fragments, the difference was reduced to a factor of < or =10. This result and the fact that M(+), M + H or M + 2H are even-electron species make it very likely that the recorded fragments were not formed directly out of the (protonated) parent ions M(+), M + H or M + 2H. In the negative mode, none of the recorded spectra contained molecular information. Only signals originating from some characteristic elements of the molecules (F, Cl), the anionic counter ion signal and some low-mass organic ions were detected. A comparative study was made between TOF-S-SIMS, using Ga(+) primary ions, and other mass spectrometric techniques, namely fast atom bombardment (FAB), electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). The measurements showed that MALDI, ESI and FAB all give rise to spectra containing molecular ion signals. ESI and FAB produced M(+) and M + H signals, originating from the cationic and zwitterionic dyes, in the positive mode and M(-) and M - H signals of the anionic and zwitterionic dyes in the negative mode. With MALDI, molecular ion signals were measured in both modes for all the dyes. Structural fragment ions were detected for FAB, ESI and MALDI in both the positive and negative modes. Compared with the other techniques, TOF-S-SIMS induced a higher degree of fragmentation.
一系列阳离子、两性离子和阴离子型氟化碳菁染料旋涂在硅基底上，在Ga(+)一次离子轰击下，采用飞行时间静态二次离子质谱(TOF-S-SIMS)进行测量。针对所有测量的染料绘制了详细的碎片模式。在正模式下，所得光谱显示阳离子染料的前体离子信号非常强烈，而阴离子染料的质子化信号几乎检测不到。阳离子染料和阴离子染料的二次离子信号强度分别反复观察到三个数量级的差异。所有测量的染料产生的质谱都包含几个特征碎片离子。尽管阳离子染料碎片的二次离子产率仍高于阴离子染料碎片，但差异缩小到<或=10倍。这一结果以及M(+)、M + H或M + 2H是偶电子物种这一事实，使得记录的碎片很可能不是直接由(质子化)母体离子M(+)、M + H或M + 2H形成的。在负模式下，记录的光谱中均不包含分子信息。仅检测到源自分子某些特征元素(F、Cl)的信号、阴离子抗衡离子信号和一些低质量有机离子。使用Ga(+)一次离子的TOF-S-SIMS与其他质谱技术，即快原子轰击(FAB)、电喷雾电离(ESI)和基质辅助激光解吸/电离(MALDI)进行了比较研究。测量结果表明，MALDI、ESI和FAB都能产生包含分子离子信号的光谱。ESI和FAB在正模式下产生源自阳离子和两性离子染料的M(+)和M + H信号，在负模式下产生阴离子和两性离子染料的M(-)和M - H信号。使用MALDI，在两种模式下都测量了所有染料的分子离子信号。在正模式和负模式下，FAB、ESI和MALDI都检测到了结构碎片离子。与其他技术相比，TOF-S-SIMS诱导的碎片化程度更高。
