ETH Zurich, Department of Chemistry and Applied Biosciences, CH-8093 Zürich Switzerland.
J Chromatogr A. 2011 Jun 10;1218(23):3704-10. doi: 10.1016/j.chroma.2011.04.030. Epub 2011 Apr 16.
Electrosonic spray ionization (ESSI) has been studied as an interface between high-performance liquid chromatography (HPLC) and mass spectrometry (MS), using sample flow rates up to 3.0 ml min⁻¹. This ionization interface was compared with pneumatically assisted electrospray ionization (ESI) using mass spectrometry for detection. For experiments that did not involve direct comparison of different flow rates, the ESI experiments were performed using post column splitting to work at optimal conditions. ESSI allows the interfacing of conventional or high-resolution liquid chromatography (LC) methods to mass spectrometry without post column splitting. High sample flow rates could be handled without a significant loss of signal intensity using a nebulization gas flow rate of 5.5 L min⁻¹. Since ESI needs to be operated with lower sample flow rates, it is limited to micro/nano LC systems, or post column splitting must be used. In particular, nano LC systems have to be treated with great care and require constant maintenance. When using post-column splitting, the increased diffusion can become a problem especially when using systems with very small void volumes. In all experiments ESSI showed better signal intensities than a commercially available, pneumatically assisted ESI source. ESSI does not require heating of the nebulizer gas, which should help to preserve the original structure of thermally unstable molecules. Therefore, ESSI is presented as an alternative to the commercially available heated ESI sources of AB SCIEX, Thermo Fischer, Agilent and Waters. The observed LC-ESSI-MS ion chromatograms are shown to be very stable even when using flow rates higher than 1.0 ml min⁻¹, which could be very suitable for ultra high performance LC, where sample flow rates up to 2.0 mL min⁻¹ with backpressures up to 1200 bar are used. Also, a difference in the relative intensities of singly and doubly protonated peptide monomers and dimers was observed between the two ionization methods. The coefficients of determination for the calibration of instrument response for Val-Tyr-Val and Met-Enkephalin showed excellent linearity over a wide concentration range (0.1-100 μM), while ESI results were only linear over a much smaller range (0.1-20 μM). The observed behavior is thought to be caused by insufficient ionization efficiency of solutions above ∼20 μM by ESI, exemplifying the robustness of ESSI as an interface between LC and MS.
电喷雾离子化（ESI）已被研究作为高效液相色谱（HPLC）和质谱（MS）之间的接口，使用的样品流速高达 3.0 ml min⁻¹。该离子化接口与气动辅助电喷雾离子化（ESI）进行了比较，ESI 采用质谱进行检测。对于不涉及不同流速直接比较的实验，ESI 实验采用柱后分流来在最佳条件下工作。ESSI 允许在没有柱后分流的情况下将常规或高分辨率液相色谱（LC）方法与质谱连接。使用 5.5 L min⁻¹ 的雾化气流速，可以在不显著损失信号强度的情况下处理高样品流速。由于 ESI 需要以较低的样品流速运行，因此它仅限于微/纳 LC 系统，或者必须使用柱后分流。特别是，纳 LC 系统需要特别小心处理，并需要经常维护。当使用柱后分流时，特别是在使用体积非常小的系统时，增加的扩散可能会成为一个问题。在所有实验中，ESSI 显示出比市售的气动辅助 ESI 源更好的信号强度。ESSI 不需要加热雾化气体，这有助于保留热不稳定分子的原始结构。因此，ESSI 被提出作为 AB SCIEX、Thermo Fischer、Agilent 和 Waters 市售加热 ESI 源的替代方案。即使使用高于 1.0 ml min⁻¹ 的流速，也可以观察到非常稳定的 LC-ESSI-MS 离子色谱图，这对于超高效液相色谱（UPLC）非常有用，其中样品流速高达 2.0 ml min⁻¹，背压高达 1200 bar。此外，还观察到两种离子化方法中单质子化和双质子化肽单体和二聚体的相对强度存在差异。Val-Tyr-Val 和 Met-Enkephalin 的仪器响应校准的决定系数在很宽的浓度范围内（0.1-100 μM）表现出极好的线性，而 ESI 结果仅在小得多的范围内（0.1-20 μM）呈线性。观察到的行为被认为是由于 ESI 对溶液的电离效率不足，溶液浓度高于约 20 μM，这体现了 ESSI 作为 LC 和 MS 之间接口的稳健性。
