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 = m /Δm = 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