Department of Chemistry, Washington State University , Pullman, Washington 99163, United States.
College of Life Science, Tarim University , Alar, Xinjiang 843300, China.
Anal Chem. 2017 Mar 7;89(5):2800-2806. doi: 10.1021/acs.analchem.6b03727. Epub 2017 Feb 16.
Although higher resolving powers are often achieved using ambient pressure drift tube ion mobility mass spectrometry (DT-IMMS) systems, lower duty cycles are often required which directly impacts sensitivity. Moreover, the mechanism of ion gating using Bradbury-Nielsen or Tyndall-Gate configurations routinely results in ion gate depletion effects which discriminate against low mobility ions. This paper reports a new method of ambient pressure ion mobility operation in which inverse ion mobility spectrometry is coupled to a time-of-flight mass spectrometer to improve sensitivity and minimize the effects of ion gate depletion. In this mode of operation, the duty cycle is improved to approximate 99% from a typical value of less than 1%, improving the signal intensity by over 2 orders of magnitude. Another advantage of inverse ion mobility mass spectrometry is a reduction of the impact of ion gate depletion on low mobility molecules that translates into higher sensitivity for this class of analytes. To demonstrate these benefits afforded by this instrumental mode of operation differences in sensitivity, resolving power, and ion discrimination are compared between the inverse and normal modes of operation using tetraalkylammonium standards. These results show that the ion throughput is significantly increased for analytes with a broad range of mobilities with little impact on resolving power. While the mobility-based discrimination is minimized using the inverse mode of operation, the noise level in the inverse mode is highly dependent upon the stability of ionization source.
虽然使用环境压力漂移管离子淌度质谱（DT-IMMS）系统通常可以实现更高的分辨率，但通常需要更低的占空比，这直接影响灵敏度。此外，使用 Bradbury-Nielsen 或 Tyndall-Gate 配置的离子门控机制通常会导致离子门控耗尽效应，从而对低迁移率离子产生歧视。本文报道了一种新的环境压力离子淌度操作方法，即将逆离子淌度谱与飞行时间质谱仪耦合，以提高灵敏度并最小化离子门控耗尽的影响。在这种操作模式下，占空比从典型值小于 1%提高到接近 99%，信号强度提高了超过 2 个数量级。逆离子淌度质谱的另一个优点是减少了离子门控耗尽对低迁移率分子的影响，从而提高了这类分析物的灵敏度。为了证明这种仪器操作模式带来的好处，使用四烷基铵标准品比较了逆模式和正常模式下的灵敏度、分辨率和离子歧视的差异。这些结果表明，对于具有广泛迁移率的分析物，离子吞吐量显著增加，而对分辨率的影响很小。虽然使用逆模式可以最小化基于迁移率的歧视，但逆模式下的噪声水平高度依赖于电离源的稳定性。
