基于电喷雾电离源质谱仪系统的八电极线性离子阱性能研究

Design and Performance Investigation of Octa-electrode Linear Ion Trap Based on an Electrospray Ionization Mass Spectrometer

八电极线性离子阱在前期的理论模拟研究中取得了较好的质量分析性能,为验证理论模拟结果,选择其中最优的结构参数,设计、加工并组装了八电极线性离子阱实物,以此为基础搭建电喷雾电离源质谱测试系统。在传统射频电压施加模式下,测试八电极线性离子阱的分析性能。当扫描速度为765 u/s时,八电极线性离子阱获得离子峰的半峰宽可达0.3 u,对应利血平(m/z 609)的质量分辨率为2030。当分析浓度为10 mg/m^(3)的利血平样品时,对应的质谱峰信噪比可达45.8。本文进一步研究了扫描速度对质量分辨率和灵敏度的影响,实现了离子碰撞诱导解离,分析了不同浓度的25羟基维生素D2标准样品,线性动态范围可达4个数量级。结果表明,八电极线性离子阱具有良好的分析性能,可为结构简化线性离子阱的研究提供全新思路,推动小型化离子阱质谱仪的研究进展。

The octa-electrode linear ion trap(OeLIT)had achieved great analytical performance in our previous theoretical simulation studies.In order to verify the accuracy of the simulation results and to test its actual mass analysis capacity in mass spectrometer,OeLIT was designed,fabricated and assembled using the optimal structure parameters achieved by the previous simulation.It was mainly composed by eight identical columnar electrodes with bevel shaped and two planar electrodes,which were fabricated from stainless steel.The external dimension of OeLIT was 62 mm×36 mm×44 mm and its internal volume was about 3.5 cm^(3).Unlike the majority of simplified ion traps with“stretched”structures,the OeLIT had a completely centrosymmetric structure,which was much simpler and had larger mechanical tolerances.The whole OeLIT could be assembled by hands and its total mechanical error was measured less than 10μm.Based on the structure of OeLIT,a mass spectrometer was developed with three-stage vacuum,and the OeLIT was placed in the third chamber with the optimized pressure of 0.002 Pa.Besides,the instrument also included an electrospray ionization source,an ion guide,an ion detector,and electronics.Here,the two electrodes on the same side were defined as a group,so there were four groups of electrodes in the OeLIT.The width between the two electrodes in one group was 0.8 mm for ion ejection,which replaced the electrode-slit design of traditional linear ion traps and was beneficial to the mass resolution.The traditional radio frequency(RF)voltage application mode was used that two balanced RF signals with 180°phase shift were applied to alternate groups of electrodes,and the performance of OeLIT was experimentally characterized with the reserpine solution.When the scan rate was 756 u/s,mass peak with FWHM of 0.3 u was achieved for ions with m/z 609,which corresponded to a mass resolution of 2030.The signal to noise ratio was up to 45.8 when analyzing the reserpine solution with a concentration of 10 mg/m^(3).The influence of scan rate on mass resolution and sensitivity was explored in detail.Two-stage tandem mass spectrometry was successfully performed in OeLIT,and the collision-induced dissociation efficiency was 36%without buffer gas.The 25 hydroxyvitamin D2 standard samples at different concentrations were quantitatively analyzed,and the linear dynamic range was 4 orders of magnitude.The experimental results show that OeLIT has good analytical performance,which confirms to the simulation results.It can provide a brand new idea for the research of ion traps with simplified structure,which will promote the development of miniaturized ion trap mass spectrometers.