Department of Chemistry, Wayne State University, Detroit, Michigan 48202, United States.
Anal Chem. 2012 Nov 6;84(21):9079-84. doi: 10.1021/ac301665h. Epub 2012 Oct 24.
This is the first report of imaging mass spectrometry (MS) from multiply charged ions at vacuum. Laserspray ionization (LSI) was recently extended to applications at vacuum producing electrospray ionization-like multiply charged ions directly from surfaces using a commercial intermediate pressure matrix-assisted laser desorption/ionization ion mobility spectrometry (IMS) MS instrument. Here, we developed a strategy to image multiply charged peptide ions. This is achieved by the use of 2-nitrophloroglucinol as matrix for spray deposition onto the tissue section and implementation of "soft" acquisition conditions including lower laser power and ion accelerating voltages similar to electrospray ionization-like conditions. Sufficient ion abundance is generated by the vacuum LSI method to employ IMS separation in imaging multiply charged ions obtained on a commercial mass spectrometer ion source without physical instrument modifications using the laser in the commercially available reflection geometry alignment. IMS gas-phase separation reduces the complexity of the ion signal from the tissue, especially for multiply charged relative to abundant singly charged ions from tissue lipids. We show examples of LSI tissue imaging from charge state +2 of three endogenous peptides consisting of between 1 and 16 amino acid residues from the acetylated N-terminal end of myelin basic protein: mass-to-charge (m/z) 795.81 (+2) molecular weight (MW) 1589.6, m/z 831.35 (+2) MW 1660.7, and m/z 917.40 (+2) MW 1832.8.
这是真空条件下多电荷离子成像质谱（MS）的首次报道。激光喷雾电离（LSI）最近被扩展到真空应用中，使用商业中间压力基质辅助激光解吸/电离离子淌度谱（IMS）MS 仪器，直接从表面产生类似于电喷雾电离的多电荷离子。在这里，我们开发了一种对多电荷肽离子进行成像的策略。这是通过使用 2-硝基邻苯二酚作为基质进行喷雾沉积到组织切片上，并采用“软”采集条件来实现的，包括较低的激光功率和离子加速电压，类似于电喷雾电离条件。真空 LSI 方法产生了足够的离子丰度，使得可以在商业质谱仪离子源上对获得的多电荷离子进行 IMS 分离，而无需对物理仪器进行修改，只需使用商业可用反射几何结构中的激光即可。IMS 气相分离减少了来自组织的离子信号的复杂性，特别是对于多电荷离子相对于组织脂质中的丰富单电荷离子。我们展示了来自髓鞘碱性蛋白乙酰化 N 端的三个内源性肽的电荷状态+2 的 LSI 组织成像示例，它们由 1 到 16 个氨基酸残基组成：质荷比（m/z）795.81（+2）分子量（MW）1589.6、m/z 831.35（+2）MW 1660.7 和 m/z 917.40（+2）MW 1832.8。
