Abstract:
RATIONALE : Many chemical processes operate at unsteady state and require a rapid mass analysis of transients with high resolution. An atmospheric pressure interface multi-reflection time-of-flight mass spectrometer (API-MRTOF-MS) has the potential to be a powerful process analytical tool.
METHODS : The ion flight path of the API-MRTOF-MS was extended from meters to over one kilometer, and the mass resolution was increased to an ultra-high level. Furthermore, the mass analysis could be done at around ten milliseconds due to the rapidity of TOFMS. The mass analyzer reflects ions via electrostatic mirrors and directs them along a folded flight path, significantly increasing flight distances and theoretically with no upper limit. The powerful API, equipped with two quadrupoles, makes the API-MRTOF-MS suitable for complex mass spectrometry methods with alternative ion selection schemes.
RESULTS : A mass resolution of 116,050 for Cs+ions is achieved within a total time-of-flight of only 18 ms. An ion transmission efficiency of over 50% was achieved after 600 cycles.
CONCLUSIONS : The performance of the API-MRTOF-MS demonstrates that it is exceedingly suitable for high-resolution process analysis, particularly for transient process analysis, due to its fast analysis speed and high-selectivity.
Keywords : Multi-reflection time-of-flight mass spectrometer, atmospheric pressure interface, high-resolution, rapid mass analysis, process analytical technology
Introduction
With continuous improvement over the past 30 years, multi-reflection time-of-flight mass spectrometer1, 2 (MRTOF-MS) was established as a potent analysis tool in physics3-14 for its ability to perform high-resolution and fast mass analysis. These properties are also essential for analysis in chemistry, biology, and medicine15-20. Meanwhile, process analysis has become an emerging discipline in analytical sciences that poses special requirements on analytical techniques21-25, particularly in the context of transient process analysis26. This type of process analysis requires high analyzing speed. The MRTOF-MS may couple with various ionizations and meet all requirements through an atmospheric pressure interface (API), which makes it an effective process analytical instrument.
Several groups have attempted to couple atmospheric ionization27-29 with the MRTOF-MS for various applications. T. Dickel et al.30, 31 developed a compact MRTOF-MS for in-situ applications by directly connecting a simple API to the apparatus. S. Naimi et al.32 coupled electrospray ionization (ESI) with MRTOF-MS using an ion carpet device to offer a reference ion for nuclear mass measurements. Other studies that share a similar geometry with the MRTOF analyzer as a linear electrostatic ion trap 33, 34 also presented various designs35, 36 with API. While these types of instruments have not been developed up until now. A. Verentchikov et al.37, 38 introduced a planar MRTOF technique, and the company Waters launched its new product, MRT39, which utilizes this planar MRTOF technique and has a resolving power of 200,000. Thermo Scientific also introduced a high-resolution product called Orbitrap Astral 40, containing a similar planar MRTOF with a resolving power of 80,000. Planar MRTOF has a wider mass range than an axial MRTOF, but it requires more control over the energy distribution in the perpendicular direction. This energy distribution sets limits on the flight length and resolution.
In this study, we introduce an atmospheric pressure interface multi-reflection time-of-flight mass spectrometer (API-MRTOF-MS) that can do the high-resolution and rapid mass spectrometry with alternative ion selection schemes. The analyzer design is based on the ZD-MRTOF-MS41, 42 from KEK (Japan) at the SLOWRI facility 43, which achieves unprecedented mass resolving powers, i.e.,R FWHM = mm = t /2Δt> 1 × 106, where 𝑚 and t are the ion’s mass and time of flight, whereas Δm and Δt are the full widths at half maximum (FWHM) of the mass and TOF spectral peaks, respectively. A set of ion transmission devices is specially designed for coupling with atmospheric ionizations, which could improve the duty cycle and supply a variety of ion selection capabilities. A differential pumping system that covers a massive pressure difference of 10 orders of magnitude is introduced. Test results of performance of the instrument are presented.
Apparatus