Chemistry Department, Indiana University , 800 East Kirkwood Avenue, Bloomington, Indiana 47401, United States.
Anal Chem. 2015 Oct 20;87(20):10330-7. doi: 10.1021/acs.analchem.5b02324. Epub 2015 Sep 29.
Charge detection mass spectrometry (CDMS) is a single-particle technique where the masses of individual ions are determined from simultaneous measurement of each ion's mass-to-charge ratio (m/z) and charge. CDMS has many desirable features: it has no upper mass limit, no mass discrimination, and it can analyze complex mixtures. However, the charge is measured directly, and the poor accuracy of the charge measurement has severely limited the mass resolution achievable with CDMS. Since the charge is quantized, it needs to be measured with sufficient accuracy to assign each ion to its correct charge state. This goal has now been largely achieved. By reducing the pressure to extend the trapping time and by implementing a novel analysis method that improves the signal-to-noise ratio and compensates for imperfections in the charge measurement, the uncertainty has been reduced to less than 0.20 e rmsd (root-mean-square deviation). With this unprecedented precision peaks due to different charge states are resolved in the charge spectrum. Further improvement can be achieved by quantizing the charge (rounding the measured charge to the nearest integer) and culling ions with measured charges midway between the integral values. After ions with charges more than one standard deviation from the mean are culled, the fraction of ions assigned to the wrong charge state is estimated to be 6.4 × 10(-5) (i.e., less than 1 in 15 000). Since almost all remaining ions are assigned to their correct charge state, the uncertainty in the mass is now almost entirely limited by the uncertainty in the m/z measurement.
电荷检测质谱（CDMS）是一种单颗粒技术，其中单个离子的质量是通过同时测量每个离子的质荷比（m/z）和电荷来确定的。CDMS 具有许多理想的特性：它没有质量上限，没有质量歧视，并且可以分析复杂的混合物。然而，电荷是直接测量的，电荷测量的精度较差严重限制了 CDMS 可实现的质量分辨率。由于电荷是量子化的，因此需要足够的精度来将每个离子分配到其正确的电荷状态。这一目标现在已经基本实现。通过降低压力以延长捕获时间，并采用一种新颖的分析方法来提高信噪比并补偿电荷测量中的不完美，不确定性已降低到小于 0.20 e rmsd（均方根偏差）。凭借这种前所未有的精度，可以在电荷谱中分辨出由于不同电荷状态而产生的峰。通过量化电荷（将测量电荷四舍五入到最接近的整数）并剔除测量电荷介于整数之间的离子，可以进一步提高精度。在剔除电荷超过平均值一个标准差的离子后，估计被错误分配电荷状态的离子分数为 6.4×10(-5)（即，少于 15000 个中的 1 个）。由于几乎所有剩余的离子都被分配到了它们的正确电荷状态，因此质量的不确定性现在几乎完全受到 m/z 测量的不确定性的限制。
