Falick A M, Medzihradszky K F, Walls F C
Department of Pharmaceutical Chemistry, University of California, San Francisco 94143-0446.
Rapid Commun Mass Spectrom. 1990 Sep;4(9):318-22. doi: 10.1002/rcm.1290040905.
Several types of artifacts were shown to be present in 4-sector tandem collision-induced dissociation (CID) mass spectra. In CID spectra of protonated peptides produced by liquid secondary-ion mass spectrometry (LSIMS), peaks corresponding to successive losses of matrix molecules from the precursor ion were observed. In addition, peaks corresponding to MH+ ions of smaller peptides that were also present in the sample/matrix mixture in greater abundance than the selected precursor ion were observed. Both of these types of artifact peaks were shown to originate from the 'peak-at-every-mass' chemical noise at the same nominal mass as that selected by the first 2 sectors (MS1). These noise ions are transmitted through to the collision cell and produce fragments that are analysed and detected in the next 2 sectors (MS2). A second, unrelated, kind of artifact was found to be due to decompositions in the second field-free region of MS2 in an EBEB geometry machine. These artifacts, which are detectable over only a very limited mass range when using a conventional single-point detector, can be present over a much greater mass range when an array detector is used and when the collision cell is floated above ground potential. A clear understanding of the origins of all peaks in a CID spectrum is important in order to have a firm foundation for interpretation, manual or computer-aided, of the spectra of unknown compounds.
研究表明，在四扇区串联碰撞诱导解离（CID）质谱中存在几种类型的伪峰。在液相二次离子质谱（LSIMS）产生的质子化肽的CID谱中，观察到与前体离子连续损失基质分子相对应的峰。此外，还观察到对应于较小肽的MH+离子的峰，这些较小肽在样品/基质混合物中的丰度也高于所选的前体离子。这两种类型的伪峰均显示源自与前两个扇区（MS1）所选标称质量相同的“每质量处有峰”的化学噪声。这些噪声离子传输到碰撞池，并产生碎片，这些碎片在接下来的两个扇区（MS2）中进行分析和检测。发现另一种不相关的伪峰是由于在EBEB几何结构仪器中MS2的第二个无场区发生分解所致。当使用传统单点检测器时，这些伪峰仅在非常有限的质量范围内可检测到，而当使用阵列检测器且碰撞池浮于地电位之上时，它们可出现在更大的质量范围内。为了为手动或计算机辅助解释未知化合物的光谱奠定坚实基础，清楚了解CID谱中所有峰的来源非常重要。
