Chen Li, Yap Yee Leng
Bioinformatics Institute, Singapore.
J Am Soc Mass Spectrom. 2008 Jan;19(1):46-54. doi: 10.1016/j.jasms.2007.10.015.
This study describes a new algorithm for charge state determination of complex isotope-resolved mass spectra. This algorithm is based on peak-target Fourier transform (PTFT) of isotope packets. It is modified from the widely used Fourier transform method because Fourier transform may give ambiguous charge state assignment for low signal-to-noise ratio (S/N) or overlapping isotopic clusters. The PTFT algorithm applies a novel "folding" strategy to enhance peaks that are symmetrically spaced about the targeted peak before applying the FT. The "folding" strategy multiplies each point to the high-m/z side of the targeted peak by its counterpart on the low-m/z side. A Fourier transform of this "folded" spectrum is thus simplified, emphasizing the charge state of the "chosen" ion, whereas ions of other charge states contribute less to the transformed data. An intensity-dependent technique is also proposed for charge state determination from frequency signals. The performance of PTFT is demonstrated using experimental electrospray ionization Fourier transform ion cyclotron resonance mass spectra. The results show that PTFT is robust for charge state determination of low S/N and overlapping isotopic clusters, and also useful for manual verification of potential hidden isotopic clusters that may be missed by the current analysis algorithms, i.e., AID-MS or THRASH.
本研究描述了一种用于确定复杂的同位素分辨质谱电荷状态的新算法。该算法基于同位素包的峰目标傅里叶变换（PTFT）。它是对广泛使用的傅里叶变换方法进行修改而来，因为对于低信噪比（S/N）或重叠同位素簇，傅里叶变换可能会给出模糊的电荷状态分配。PTFT算法应用了一种新颖的“折叠”策略，在应用傅里叶变换之前增强围绕目标峰对称分布的峰。“折叠”策略将目标峰高m/z侧的每个点与其低m/z侧的对应点相乘。这样，对这个“折叠”谱进行傅里叶变换就得到简化，突出了“选定”离子的电荷状态，而其他电荷状态的离子对变换后的数据贡献较小。还提出了一种基于频率信号的强度相关技术用于电荷状态确定。使用实验性电喷雾电离傅里叶变换离子回旋共振质谱展示了PTFT的性能。结果表明，PTFT对于低S/N和重叠同位素簇的电荷状态确定具有鲁棒性，并且对于人工验证当前分析算法（即AID-MS或THRASH）可能遗漏的潜在隐藏同位素簇也很有用。
