Simplifying CE-MS operation. 2. Interfacing low-flow separation techniques to mass spectrometry using a porous tip
Simplifying CE-MS operation. 2. Interfacing low-flow separation techniques to mass spectrometry using a porous tip
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DOI：
10.1021/ac0704560
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发表时间：
2007-06-01
影响因子：
7.4
通讯作者：
Moini, Mehdi
中科院分区：
文献类型：
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作者：
Moini, Mehdi
介绍了一种在无鞘毛细管电泳（CE）和纳米液相色谱（nLC）等低流速分离技术与电喷雾离子化（ESI）质谱（MS）之间的稳健、可重复和单步接口设计。在该设计中，通过毛细管出口处的多孔尖端实现与毛细管出口的电连接。通过移除1-1.5 in.的聚酰亚胺涂层的毛细管和蚀刻这一部分，用49%的HF溶液，直到它是多孔的。通过将含有多孔尖端的毛细管出口插入现有的ESI针（金属护套）并用背景电解质填充针，即可简单地实现与毛细管出口的电连接。水在ESI针处的氧化还原反应以及这些小离子通过多孔尖端进入毛细管的传输为ESI和CE出口电极提供了电连接。腐蚀过程将包括毛细管尖端在内的腐蚀部分的壁厚减小到5-10 μ m，对于内径为20-30 μ m的毛细管，毛细管在类似于1.5kV下产生稳定的电喷雾。该设计适用于通过ESI将具有宽范围流速的宽范围毛细管尺寸连接到MS，但它特别适用于连接窄（< 30 μ m i. d.）毛细管和低流速（< 100 nL/min）。多孔头端设计的优点包括：（1）其制造可重复，可自动化，不需要任何机械工具。(2)蚀刻工艺减小了尖端外径，并在一个步骤中使毛细管多孔。(3)该接口可用于nLC-MS和CE-MS。（4）如果堵塞或损坏，尖端的一小部分可以被蚀刻掉，而不会损失任何性能。(5)接口设计使毛细管内壁保持完整，因此不会向CE-MS或nLC-MS接口增加任何死体积。(6)由于水在高压电极处的氧化还原反应而形成的气泡在分离毛细管的外部，并且不影响分离或MS性能。该接口的性能证明了氨基酸，肽和蛋白质混合物的分析。
A robust, reproducible, and single-step interface design between low flow rate separation techniques, such as sheathless capillary electrophoresis (CE) and nanoliquid chromatography (nLC), and mass spectrometry (MS) using electrospray ionization (ESI), is introduced. In this design, the electrical connection to the capillary outlet was achieved through a porous tip at the capillary outlet. The porous section was created by removing 1-1.5 in. of the polyimide coating of the capillary and etching this section by 49% solution of HF until it is porous. The electrical connection to the capillary outlet is achieved simply by inserting the capillary outlet containing the porous tip into the existing ESI needle (metal sheath) and filling the needle with the background electrolyte. Redox reactions of water at the ESI needle and transport of these small ions through the porous tip into the capillary provides the electrical connection for the ESI and for the CE outlet electrode. The etching process reduces the wall thickness of the etched section, including the tip of the capillary, to 5-10 mu m, which for a 20-30 mu m i.d. capillary results in stable electrospray at similar to 1.5 kV. The design is suitable for interfacing a wide range of capillary sizes with a wide range of flow rates to MS via ESI, but it is especially useful for interfacing narrow (< 30 mu m i.d.) capillaries and low flow rates (< 100 nL/min). The advantages of the porous tip design include the following: (1) its fabrication is reproducible, can be automated, and does not require any mechanical tools. (2) The etching process reduces the tip outer diameter and makes the capillary porous in one step. (3) The interface can be used for both nLC-MS and CE-MS. (4) If blocked or damaged, a small section of the tip can be etched off without any loss of performance. (5) The interface design leaves the capillary inner wall intact and, therefore, does not add any dead volume to the CE-MS or nLC-MS interface. (6) Bubble formation due to redox reactions of water at the high-voltage electrode is outside of the separation capillary and does not affect separation or MS performances. The performance of this interface is demonstrated by the analyses of amino acids, peptide, and protein mixtures.