Wong Richard L, Amster I Jonathan
Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, USA.
J Am Soc Mass Spectrom. 2006 Dec;17(12):1681-91. doi: 10.1016/j.jasms.2006.07.019. Epub 2006 Aug 24.
A new external calibration procedure for FT-ICR mass spectrometry is presented, stepwise-external calibration. This method is demonstrated for MALDI analysis of peptide mixtures, but is applicable to any ionization method. For this procedure, the masses of analyte peaks are first accurately measured at a low trapping potential (0.63 V) using external calibration. These accurately determined (< 1 ppm accuracy) analyte peaks are used as internal calibrant points for a second mass spectrum that is acquired for the same sample at a higher trapping potential (1.0 V). The second mass spectrum has a approximately 10-fold improvement in detection dynamic range compared with the first spectrum acquired at a low trapping potential. A calibration equation that accounts for local and global space charge is shown to provide mass accuracy with external calibration that is nearly identical to that of internal calibration, without the drawbacks of experimental complexity or reduction of abundance dynamic range. For the 609 mass peaks measured using stepwise-external calibration method, the root-mean-square error is 0.9 ppm. The errors appear to have a Gaussian distribution; 99.3% of the mass errors are shown to lie within three times the sample standard deviation (2.6 ppm) of their true value.
本文介绍了一种用于傅里叶变换离子回旋共振质谱（FT-ICR MS）的新型外部校准程序——逐步外部校准。该方法已在肽混合物的基质辅助激光解吸电离（MALDI）分析中得到验证，但适用于任何电离方法。在此程序中，首先使用外部校准在低捕获电位（0.63 V）下准确测量分析物峰的质量。这些精确测定（准确度<1 ppm）的分析物峰用作第二个质谱的内部校准点，第二个质谱是在相同样品的较高捕获电位（1.0 V）下采集的。与在低捕获电位下采集的第一个质谱相比，第二个质谱的检测动态范围提高了约10倍。一个考虑了局部和全局空间电荷的校准方程表明，通过外部校准可提供与内部校准几乎相同的质量准确度，且没有实验复杂性或丰度动态范围降低的缺点。对于使用逐步外部校准方法测量的609个质量峰，均方根误差为0.9 ppm。误差似乎呈高斯分布；99.3%的质量误差显示在其真实值的三倍样本标准差（2.6 ppm）范围内。
