Lee Kenneth W, Harrilal Christopher P, Fu Liangxuan, Eakins Gregory S, McLuckey Scott A
Department of Chemistry, Purdue University, West Lafayette, IN, 47907-2084, USA.
Int J Mass Spectrom. 2020 Dec;458. doi: 10.1016/j.ijms.2020.116437. Epub 2020 Sep 20.
Native mass spectrometry (MS) focuses on measuring the masses of large biomolecular complexes and probing their structures. Large biomolecular complexes are readily introduced into mass spectrometers as gas-phase ions using electrospray ionization (ESI); however, the ions tend to be heavily adducted with solvent and salts, which leads to mass measurement errors. Various solution clean-up approaches can reduce the degree of adduction prior to introduction to the mass spectrometer. Gas-phase activation of trapped ions can provide additional adduct reduction, and charge reduction ion/ion reactions increase charge state separation. Together, gas-phase activation and charge reduction can combine to yield spectra of well separated charge states for improved mass measurements. A simple gas-phase collisional activation technique is to apply a dipolar DC (DDC) field to opposing electrodes in an ion trap. DDC activation loses its efficacy when ions are trapped at low values, which is true of the high ions generated by charge reduction ion/ion reactions. Digital ion trapping (DIT) readily traps high ions at higher values by varying trapping frequency rather than amplitude, but the low frequencies used to trap high ions also decreases the efficacy of DDC activation. We demonstrate here using ions derived from GroEL that IR activation of ions shows no discrimination against high ions trapped with DIT, because they can be focused equally well to the trap center to interact with the IR laser beam. Following pump out of excess background gas, IR activation can also induce efficient dissociation of the GroEL complex. This work demonstrates that IR activation is an effective approach for ion heating in native MS over the unusually wide range of charge states accessible via gas-phase ion/ion reactions.
原生质谱（MS）专注于测量大型生物分子复合物的质量并探究其结构。使用电喷雾电离（ESI）可轻松将大型生物分子复合物作为气相离子引入质谱仪中；然而，这些离子往往会大量与溶剂和盐结合，从而导致质量测量误差。在引入质谱仪之前，各种溶液清理方法可降低结合程度。捕获离子的气相活化可进一步减少加合物，而电荷减少离子/离子反应可增加电荷态分离。气相活化和电荷减少共同作用，可产生电荷态分离良好的光谱，以改善质量测量。一种简单的气相碰撞活化技术是在离子阱的相对电极上施加偶极直流（DDC）场。当离子在低值下被捕获时，DDC活化会失去其功效，电荷减少离子/离子反应产生的高值离子就是这种情况。数字离子阱（DIT）通过改变捕获频率而非幅度，很容易在较高值下捕获高值离子，但用于捕获高值离子的低频也会降低DDC活化的功效。我们在此使用源自GroEL的离子证明，离子的红外（IR）活化对用DIT捕获的高值离子没有歧视，因为它们可以同样好地聚焦到阱中心与红外激光束相互作用。在抽出过量背景气体后，红外活化还可诱导GroEL复合物的有效解离。这项工作表明，红外活化是原生质谱中一种有效的离子加热方法，适用于通过气相离子/离子反应可获得的异常广泛的电荷态范围。
