Whittal R M, Li L
Department of Chemistry, University of Alberta, Edmonton, Canada.
Anal Chem. 1995 Jul 1;67(13):1950-4. doi: 10.1021/ac00109a007.
A time-lag focusing method is developed for the improvement of mass resolution in a linear time-of-flight mass spectrometer for matrix-assisted laser desorption/ionization (MALDI). In this technique, the ions generated by the MALDI process are extracted by a pulsed voltage. A short time delay (280 ns) is inserted in between the laser desorption/ionization event and the ion extraction. The region between the repeller and extraction grid is field-free during the delay. The time-lag extraction allows the ions generated in the region between the repeller and the extraction grid to separate according to their velocity (energy). Application, to the repeller, of the appropriate pulse voltage provides the energy correction necessary to simultaneously detect all ions of the same mass/charge regardless of their initial energy, resulting in improved mass resolution. It is demonstrated that mass resolution in the range of 3000-6000 fwhm can be obtained. With this mass resolution, isotopically resolved mass spectra are observed for peptides with masses up to 3000 Da. For proteins, such as bovine insulin, cytochrome c, and apomyoglobin, resolution in the range of 800-1000 fwhm is observed with a mass measurement accuracy better than 0.01%.
为了提高基质辅助激光解吸/电离（MALDI）线性飞行时间质谱仪的质量分辨率，开发了一种时间延迟聚焦方法。在该技术中，MALDI过程产生的离子通过脉冲电压提取。在激光解吸/电离事件和离子提取之间插入一个短时间延迟（280纳秒）。在延迟期间，推斥极和提取栅之间的区域无电场。时间延迟提取使在推斥极和提取栅之间区域产生的离子根据其速度（能量）分离。对推斥极施加适当的脉冲电压可提供必要的能量校正，以便同时检测所有相同质荷比的离子，而不管其初始能量如何，从而提高质量分辨率。结果表明，可以获得3000 - 6000半高宽范围内的质量分辨率。利用这种质量分辨率，观察到质量高达3000 Da的肽的同位素分辨质谱。对于蛋白质，如牛胰岛素、细胞色素c和脱辅基肌红蛋白，观察到800 - 1000半高宽范围内的分辨率，质量测量精度优于0.01%。
