Dixon R Brent, Muddiman David C, Hawkridge Adam M, Fedorov A G
W. M. Keck FT-ICR Mass Spectrometry Laboratory, Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, USA.
J Am Soc Mass Spectrom. 2007 Nov;18(11):1909-13. doi: 10.1016/j.jasms.2007.08.006. Epub 2007 Aug 16.
We report the first quantitative assessment of electrosprayed droplet/ion focusing enabled by the use of a voltage-assisted air amplifier between an electrospray ionization emitter and a hybrid linear ion trap Fourier transform ion cyclotron resonance mass spectrometer (ESI-LTQ-FT-ICR-MS). A solution of fluorescent dye was electrosprayed with a stainless steel mesh screen placed in front of the MS inlet capillary acting as a gas-permeable imaging plate for fluorescence spectroscopy. Without use of the air amplifier, no detectable FT-ICR signal was observed, as well as no detectable fluorescence on the screen upon imaging using a fluorescence scanner. When the air amplifier was turned ON while electrospraying the fluorescent dye, FT-ICR mass spectra with high signal to noise ratio were obtained with an average ion injection time of 21 ms for an AGC target value of 5 x 10(5). Imaging of the screen using a fluorescence scanner produced a distinct spot of cross-sectional area approximately 33.5 mm(2) in front of the MS inlet capillary. These experimental results provide direct evidence of aerodynamic focusing of electrosprayed droplets/ions enabled by an air amplifier, resulting in improved electrospray droplet/ion capture efficiency and reduced ion injection time. A second set of experiments was carried out to explore whether the air amplifier assists in desolvation. By electrospraying a mix of quaternary amines, ratios of increasingly hydrophobic molecules were obtained. Observation of the solvophobic effect associated with electrospray ionization resulted in a higher abundance of the hydrophobic molecule. This bias was eliminated when the air amplifier was turned ON and a response indicative of the respective component concentrations of the molecules in the bulk solution was observed.
我们报告了在电喷雾电离发射器与混合线性离子阱傅里叶变换离子回旋共振质谱仪（ESI-LTQ-FT-ICR-MS）之间使用电压辅助空气放大器实现的电喷雾液滴/离子聚焦的首次定量评估。将荧光染料溶液进行电喷雾，在质谱仪入口毛细管前放置一个不锈钢筛网，作为用于荧光光谱的透气成像板。不使用空气放大器时，未观察到可检测的傅里叶变换离子回旋共振信号，并且使用荧光扫描仪成像时屏幕上也未检测到荧光。在对荧光染料进行电喷雾时打开空气放大器，对于5×10⁵的自动增益控制（AGC）目标值，获得了具有高信噪比的傅里叶变换离子回旋共振质谱图，平均离子注入时间为21毫秒。使用荧光扫描仪对屏幕成像时，在质谱仪入口毛细管前产生了一个横截面积约为33.5平方毫米的明显斑点。这些实验结果提供了空气放大器实现电喷雾液滴/离子气动聚焦的直接证据，从而提高了电喷雾液滴/离子捕获效率并缩短了离子注入时间。进行了第二组实验以探究空气放大器是否有助于去溶剂化。通过电喷雾季胺混合物，获得了疏水性逐渐增加的分子的比例。观察到与电喷雾电离相关的疏溶剂效应导致疏水分子的丰度更高。当打开空气放大器时，这种偏差被消除，并且观察到了反映本体溶液中分子各自组分浓度的响应。
