Numerical Analysis of Ion-Funnel Transmission Efficiency in an API-MS System with a Continuum/Microscopic Approach

Ion trajectory simulation is a significant and useful tool for understanding ion transfer mechanisms within the first vacuum region of the atmospheric pressure ionization mass spectrometer (API-MS). However, the complex dynamic gas field and wide pressure range lead to inaccurate simulation and huge computational costs. In this work, a novel electrohydrodynamic simulation called the statistical diffusion–hard-sphere (SDHS) mixed collision model was developed for characterizing the ion trajectories. For the first time, the influence of the dynamic pressure on the ion trajectory is considered for simulation, which helps to avoid an intolerable computational cost. Comparing with the conventional Monte Carlo collision model, the SDHS method helps to improve the calculation accuracy of ion trajectories under the first vacuum region and reduce the computational cost for at least 12-folds. Simulation results showed that the maximum ion loss came from the gap of the electrodes. The distance of the capillary–quadrupole ion guide was also a non-negligible factor. The trend of quantitative experimental results matches the SDHS simulation results. The maximum ion transfer efficiencies of quantitative experiment and simulation were 55% and 52%, respectively. Moreover, three ions, caffeine, reserpine, and Ultramark 1621, were measured for evaluating the applicability of SDHS in real API-MS. The trend of experimental results showed good agreement with that of computation. And the results of caffeine further illustrated the reason that the small mass ion transfer efficiency decreased with increasing radio frequency voltage. SDHS method is expected to be useful in the design of ion guides for further improvement of the sensitivity of API-MS.

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Numerical Analysis and Quantification of Transfer Efficiency Coupled with Capillary and Quadrupole Ion Guide in an API-MS System

Song,

Zhang,

Dai

et al. 2024

Numerical Simulation of Ion Transport in a Nano-Electrospray Ion Source at Atmospheric Pressure

Wang

Bajic

John

et al. 2018

Understanding ion transport properties from the ion source to the mass spectrometer (MS) is essential for optimizing device performance. Numerical simulation helps in understanding of ion transport properties and, furthermore, facilitates instrument design. In contrast to previously reported numerical studies, ion transport simulations in a continuous injection mode whilst considering realistic space-charge effects have been carried out. The flow field was solved using Reynolds-averaged Navier-Stokes (RANS) equations, and a particle-in-cell (PIC) method was applied to solve a time-dependent electric field with local charge density. A series of ion transport simulations were carried out at different cone gas flow rates, ion source currents, and capillary voltages. A force evaluation analysis reveals that the electric force, the drag force, and the Brownian force are the three dominant forces acting on the ions. Both the experimental and simulation results indicate that cone gas flow rates of ≤250 slph (standard liter per hour) are important for high ion transmission efficiency, as higher cone gas flow rates reduce the ion signal significantly. The simulation results also show that the ion transmission efficiency reduces exponentially with an increased ion source current. Additionally, the ion loss due to space-charge effects has been found to be predominant at a higher ion source current, a lower capillary voltage, and a stronger cone gas counterflow. The interaction of the ion driving force, ion opposing force, and ion dispersion is discussed to illustrate ion transport mechanism in the ion source at atmospheric pressure. Graphical Abstract.

The FUNPET—a New Hybrid Ion Funnel-Ion Carpet Atmospheric Pressure Interface for the Simultaneous Transmission of a Broad Mass Range

Draper

Anthony

Jarrold

2018

An atmospheric pressure interface transports ions from ambient pressure to the low-pressure environment of a mass spectrometer. A capillary coupled to an ion funnel is widely used. However, conventional ion funnels do little to negate the large amount of energy picked up by high-mass ions from the gas flow through the capillary. There has been little work done on the effects of gas flow on ion transmission, and the previous studies have all been limited to low-mass, low-charge ions. In this work, we account for the effects of gas flow, diffusion, and electric fields (static and oscillating) on ion trajectories and use simulations to design a new hybrid ion funnel-ion carpet (FUNPET) interface that transmits a broad mass range with a single set of instrument conditions. The design incorporates a virtual jet disruptor where pressure buildup and counter flow dissipate the supersonic jet that results from gas flow into the interface. This, and the small exit aperture that can be used with the FUNPET, reduces the gas flow into the next stage of differential pumping. The virtual jet disruptor thermalizes ions with a broad range of masses (1 kDa to 1 GDa), and once thermalized, they are transmitted into next region of the mass spectrometer with low excess kinetic energy. The FUNPET interface is easy to fabricate from flexible printed circuit board and a support frame made by 3D printing. The performance of the interface was evaluated using charge detection mass spectrometry. Graphical Abstract ᅟ.