Hu Rui, Gundlach-Graham Alexander
Department of Chemistry, Iowa State University, Ames, Iowa, USA.
Rapid Commun Mass Spectrom. 2024 Jun 30;38(12):e9753. doi: 10.1002/rcm.9753.
The use of a frequency-scanned digital quadrupole mass filter (QMF) with varying duty cycles shows promise for application as a high-resolution mass analyzer design for inductively coupled plasma mass spectrometry (ICP-MS). High resolution in ICP-MS is important to overcome isobaric polyatomic interferences. Here, we explore the possibility and the characteristics of using a digital quadrupole operating in higher stability regions for ICP-MS.
We perform computational simulations in SIMION of a digital QMF that is operated by scanning the frequency of the digital waveform at a fixed driving voltage and various duty cycles. For ions in the atomic mass range (7-238 m/z), we investigate the expected resolution, transmission, fringe field effects, and ion trajectories. We compare different characteristics between sine and digital waveform QMF.
Within the capability of current digital waveform generation technology, a digital QMF can produce variable mass resolution, from several hundred to more than 10 000. This mass resolution covers the low, medium, and high resolutions that are typical for sector-field ICP-MS. Additionally, simulations suggest that transmission of the QMF remains high at high resolution. For example, with 87.50/12.50 duty cycle (zone 4,1), resolution at 10% peak width is 10 420 for m/z 80. The transmission through the quadrupole, which is constant for all isoenergetic ions, is ~2.5%, and most ion loss is due to the defocusing effects of the fringe field. Compared to sinusoidal QMFs, ions need many fewer cycles in the digital QMF to obtain high resolution.
The results demonstrate that the use of a frequency-scanned, duty-cycle-modulated digital QMF as the mass analyzer for ICP-MS has the potential to produce high resolution while maintaining considerable transmission, thus overcoming most spectral interferences in elemental MS.
使用具有不同占空比的频率扫描数字四极杆质量过滤器（QMF）有望作为电感耦合等离子体质谱（ICP-MS）的高分辨率质量分析器设计。ICP-MS中的高分辨率对于克服同量异位多原子干扰很重要。在此，我们探讨了在ICP-MS中使用在更高稳定性区域运行的数字四极杆的可能性和特性。
我们在SIMION中对数字QMF进行计算模拟，该数字QMF通过在固定驱动电压和各种占空比下扫描数字波形的频率来运行。对于原子质量范围内（7 - 238 m/z）的离子，我们研究了预期的分辨率、传输率、边缘场效应和离子轨迹。我们比较了正弦和数字波形QMF之间的不同特性。
在当前数字波形生成技术的能力范围内，数字QMF可以产生可变的质量分辨率，从几百到超过10000。这种质量分辨率涵盖了扇形场ICP-MS典型的低、中、高分辨率。此外，模拟表明QMF在高分辨率下的传输率仍然很高。例如，在87.50/12.50占空比（区域4,1）下，m/z 80在10%峰宽处的分辨率为10420。通过四极杆的传输率对于所有等能离子是恒定的，约为2.5%，并且大多数离子损失是由于边缘场的散焦效应。与正弦QMF相比，离子在数字QMF中获得高分辨率所需的周期要少得多。
结果表明，使用频率扫描、占空比调制的数字QMF作为ICP-MS的质量分析器有潜力在保持相当高传输率的同时产生高分辨率，从而克服元素质谱中的大多数光谱干扰。
