极微型双曲面线性离子阱的模拟研究

Simulation Study of an Extremely Miniature Hyperbolic Linear Ion Trap

  • 摘要: 随着微机电系统(micro-electro-mechanical system, MEMS)工艺的快速发展,芯片级质谱仪的研制逐渐成为分析仪器领域的新焦点。微型质量分析器是芯片级质谱仪的核心器件,本工作基于非硅MEMS工艺下可实现的1 mm场半径极微型双曲面线性离子阱(miniature-hyperboloid linear ion trap, M-HLIT)质量分析器,采用理论模拟方法研究了2种不同结构M-HLIT的质量分析性能。在理想结构中,系统研究了共振激发交流(alternatingcurrent, AC)信号幅值和频率、射频(radio frequency, RF)信号频率等电参数对质量分辨率的影响。在“拉伸”结构中,优化了“拉伸”比(ry/rx)、开槽宽度d、电极截断距离h等结构参数。模拟结果表明,通过对M-HLIT的系统性优化,m/z 117离子的最高质量分辨率可达551,优于相同尺寸的简化电极线性离子阱;当扫描速率降至600 Th/s时,质量分辨率可提升至1 376。该M-HLIT在处理低m/z离子时存在一定局限性,但在处理高m/z离子时具有优势。优化后的M-HLIT体积仅0.62 cm3,为传统微型线性离子阱体积的25.5%,这为芯片级质谱仪中微型质量分析器的设计提供了有效解决方案,可有力推动原位快检质谱分析技术的发展。

     

    Abstract: The miniaturization of mass spectrometers has garnered significant attention in the analytical chemistry community. Leveraging the rapid advancements in micro-electro-mechanical system (MEMS), the development of chip-scale mass spectrometers has emerged as a transformative innovation in the field of analytical instrumentation. The miniature mass analyzer serves as the core component of chip-scale mass spectrometers. This study presented an extremely miniature-hyperbolic linear ion trap (M-HLIT) mass analyzer with a field radius of 1 mm, fabricated using non-silicon MEMS technique. The mass analysis performance of two different M-HLIT structures was systematically investigated through theoretical simulation. For the ideal structure, the effects of electrical parameters, including the amplitude and frequency of the alternating current (AC) signal and the frequency of the radio frequency (RF) signal, on mass resolution were investigated. The results demonstrated that ion traps with smaller field radius require higher RF frequencies as well as lower frequency ratios (fAC/fRF) to achieve optimal resonance ejection conditions. Notably, the mass resolution for ions at m/z 117 is as high as 576. In practical applications, ion ejection slots must be integrated into the ion trap ejection electrodes, and ion detectors are employed to collect and quantify. However, the introduction of these ejection slots distorts the internal electric field distribution, increases the proportion of higher-order fields, and leads to a decrease in mass analysis performance. To address this issue, the ratio of electric field components can be optimized, and electric field distortions can be mitigated through bidirectional stretching of the ejection electrodes, a design referred to as a “stretched” structure. For the “stretched” structure, key structural parameters including stretching ratio (ry/rx), slots width (d), and electrode truncation distance (h) were optimized. Simulation results indicated that by systematically optimizing the structure of M-HLIT, the highest mass resolution for ions at m/z 117 reaches 551, outperforming similarly sized simplified electrode linear ion traps. Furthermore, when the scan rate is reduced to 600 Th/s, the mass resolution increases to 1 376, demonstrating that the structured ion trap design allows for a trade-off between scan rate and enhanced mass resolution. The M-HLIT exhibits limitations in analyzing low m/z ions (mass resolution with 87 for m/z 19) while excelling in the analysis of high m/z ions (mass resolution with 45 984 for m/z 10019). The optimized M-HLIT has a volume of only 0.62 cm3, which is merely 25.5% of the volume of conventional miniature linear ion traps, thereby significantly reducing the size and weight of conventional miniature ion traps. This innovative design offers an efficient and practical solution for miniature mass analyzers in chip-scale mass spectrometers, represents a significant advancement in the development of in-situ rapid detection mass spectrometer technology, and provides a valuable reference for sub-millimeter-scale ion traps.

     

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