Clean Energy Research Center, University of Yamanashi, 4-3-11, Takeda, Kofu, Yamanashi, 400-8511 Japan.
Analyst. 2013 Nov 7;138(21):6316-22. doi: 10.1039/c3an00699a.
Nanoelectrospray ionization (nanoESI) with a very fine emitter and nanoliter solution flow rate is known to be suitable for aqueous solutions. However, under atmospheric pressure, its stability with aqueous solutions is not always guaranteed particularly in the negative ion mode where corona and arc discharge tend to occur more easily. Electrical discharge can be quenched to a certain extent by adding electron scavenging gases like SF6 or CO2 to the ion source. The onset potential that is required to induce the discharge also increases with an increase of gas pressure. Recently, we have reported on a series of high pressure electrospray ion sources that were stable in both positive and negative ion modes using air or N2 as the working gas. In this paper, we compare the performance of nanoelectrospray under atmospheric pressure and super-atmospheric pressure for the analysis of samples in aqueous solution. The comparative study was performed using the same ion source chamber that could be pressurized up to 6 bar. The pressure in the first pumping stage of the mass spectrometer was kept constant when the ion source pressure was changed by using an additional pump with variable pumping speed. High pressure nanoESI optimized at 2-3 bar demonstrated a 3-5 times improvement in ion signal intensity compared to atmospheric pressure nanoESI, and the signal stability was significantly improved particularly in the negative mode.
纳升电喷雾电离（nanoESI）采用非常细的喷嘴和纳升级的溶液流速，适用于水溶液。然而，在大气压下，其对水溶液的稳定性并不总是得到保证，特别是在负离子模式下，更容易发生电晕放电和电弧放电。通过向离子源中添加电子捕获气体（如 SF6 或 CO2），可以在一定程度上抑制放电。放电的起始电位随着气体压力的增加而增加。最近，我们报道了一系列使用空气或 N2 作为工作气体的正、负离子模式下稳定的高压电喷雾离子源。本文比较了大气压和超大气压下纳升电喷雾在水溶液样品分析中的性能。使用相同的离子源腔，当通过使用可变抽速的附加泵改变离子源压力时，可以将其加压至 6 巴。当通过使用可变抽速的附加泵改变离子源压力时，可以将离子源腔加压至 6 巴。质谱仪的第一级泵的压力保持不变。与大气压下的纳升电喷雾相比，优化至 2-3 巴的高压纳升电喷雾的离子信号强度提高了 3-5 倍，特别是在负离子模式下，信号稳定性得到了显著提高。
