Snyder Dalton T, Pulliam Christopher J, Cooks R Graham
Department of Chemistry and Center for Analytical Instrumentation Development, Purdue University, West Lafayette, IN, 47907, USA.
Rapid Commun Mass Spectrom. 2016 May 30;30(10):1190-1196. doi: 10.1002/rcm.7550.
Mass spectra can be recorded using ion traps by scanning the frequency of an alternating current (ac) signal that corresponds to the secular frequency of a trapped ion. There is a considerable simplification in the instrumentation needed to perform such a scan compared with conventional scans of the radiofrequency (rf) amplitude. However, mass calibration is difficult. An algorithm that can be used to achieve mass calibration is investigated and the factors that affect ion mass assignments are discussed.
Time domain data, recorded using a commercial benchtop linear ion trap mass spectrometer, are converted to the m/z domain using ion Mathieu parameter q values which are derived from the dimensionless frequency parameter β expressed as a continuing fraction in terms of q . The relationship between the operating parameters of an ideal ion trap and the ion m/z ratio is derived from the Mathieu equations and expressed as an algorithm which through successive approximations yields the Mathieu q value and hence m/z values and peak widths. The predictions of the algorithm are tested against experiment by sweeping the frequency of a small supplementary ac signal so as to cause mass-selective ejection of trapped ions.
Calibration accuracy is always better than 0.1%, often much better. Peak widths correspond to a mass resolution of 250 to 500 in the m/z 100-1800 range in secular frequency scans.
A simple, effective method of calibration of mass spectra recorded using secular frequency scans is achieved. The effects of rf amplitude, scan rate, and ac amplitude on calibration parameters are shown using LTQ linear ion trap data. Corrections for differences in ion mass must be made for accurate calibration, and this is easily incorporated into the calibration procedure. Copyright © 2016 John Wiley & Sons, Ltd.
通过扫描与被俘获离子的回旋频率相对应的交变电流（ac）信号的频率，可以使用离子阱记录质谱。与传统的射频（rf）幅度扫描相比，执行这种扫描所需的仪器设备有相当大的简化。然而，质量校准很困难。本文研究了一种可用于实现质量校准的算法，并讨论了影响离子质量分配的因素。
使用商用台式线性离子阱质谱仪记录的时域数据，利用离子马蒂厄参数q值转换到m/z域，该参数q值由无量纲频率参数β导出，β以q的连分数形式表示。理想离子阱的操作参数与离子m/z比之间的关系由马蒂厄方程导出，并表示为一种算法，该算法通过逐次逼近产生马蒂厄q值，进而得到m/z值和峰宽。通过扫描一个小的辅助交流信号的频率，以便引起被俘获离子的质量选择性喷射，将该算法的预测结果与实验进行对比测试。
校准精度始终优于0.1%，通常要好得多。在回旋频率扫描中，m/z 100 - 1800范围内的峰宽对应于250至500的质量分辨率。
实现了一种使用回旋频率扫描记录质谱的简单、有效校准方法。利用LTQ线性离子阱数据展示了射频幅度、扫描速率和交流幅度对校准参数的影响。为了进行精确校准，必须对离子质量差异进行校正，并且这很容易纳入校准程序。版权所有© 2016约翰威立父子有限公司。
