Olsen Jesper V, de Godoy Lyris M F, Li Guoqing, Macek Boris, Mortensen Peter, Pesch Reinhold, Makarov Alexander, Lange Oliver, Horning Stevan, Mann Matthias
Center for Experimental BioInformatics (CEBI), Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark.
Mol Cell Proteomics. 2005 Dec;4(12):2010-21. doi: 10.1074/mcp.T500030-MCP200. Epub 2005 Oct 24.
Mass accuracy is a key parameter of mass spectrometric performance. TOF instruments can reach low parts per million, and FT-ICR instruments are capable of even greater accuracy provided ion numbers are well controlled. Here we demonstrate sub-ppm mass accuracy on a linear ion trap coupled via a radio frequency-only storage trap (C-trap) to the orbitrap mass spectrometer (LTQ Orbitrap). Prior to acquisition of a spectrum, a background ion originating from ambient air is first transferred to the C-trap. Ions forming the MS or MS(n) spectrum are then added to this species, and all ions are injected into the orbitrap for analysis. Real time recalibration on the "lock mass" by corrections of mass shift removes mass error associated with calibration of the mass scale. The remaining mass error is mainly due to imperfect peaks caused by weak signals and is addressed by averaging the mass measurement over the LC peak, weighted by signal intensity. For peptide database searches in proteomics, we introduce a variable mass tolerance and achieve average absolute mass deviations of 0.48 ppm (standard deviation 0.38 ppm) and maximal deviations of less than 2 ppm. For tandem mass spectra we demonstrate similarly high mass accuracy and discuss its impact on database searching. High and routine mass accuracy in a compact instrument will dramatically improve certainty of peptide and small molecule identification.
质量准确度是质谱性能的一个关键参数。飞行时间（TOF）仪器可达到百万分之几的低误差水平，而傅里叶变换离子回旋共振（FT-ICR）仪器在离子数量得到良好控制的情况下能够实现更高的准确度。在此，我们展示了在通过仅射频存储阱（C阱）与轨道阱质谱仪（LTQ Orbitrap）耦合的线性离子阱上实现低于百万分之一的质量准确度。在采集光谱之前，首先将源自环境空气的背景离子转移至C阱。然后将形成MS或MS(n)光谱的离子添加到该离子种类中，所有离子都注入轨道阱进行分析。通过对质量偏移进行校正，对“锁定质量”进行实时重新校准，消除与质量标度校准相关的质量误差。剩余的质量误差主要是由弱信号导致的峰形不理想造成的，可通过在LC峰上对质量测量值进行平均（按信号强度加权）来解决。对于蛋白质组学中的肽段数据库搜索，我们引入了可变质量容差，实现了平均绝对质量偏差为0.48 ppm（标准偏差为0.38 ppm），最大偏差小于2 ppm。对于串联质谱，我们展示了同样高的质量准确度，并讨论了其对数据库搜索的影响。在紧凑型仪器中实现高且常规的质量准确度将极大地提高肽段和小分子鉴定的确定性。
