4.2.3 Mass Resolving Power
After a series of optimizations that enabled a hundredfold-magnified
flight length, experiments on measuring mass resolving power with CsI
were performed. First, we investigated the mass resolution as a function
of the lap number. Then, we carefully tuned the voltage setting of the
mirror electrodes to shift the focus to the point where the best
resolution was obtained.
Fig. 9 displays the Δt andR at various laps; Δt is measured by the oscilloscope, andR is calculated by the corresponding time and Δt . As the
number of laps increased, Δt (black triangle in Fig. 9) tended to
increase rapidly at first and then slowly over hundreds of laps. The
primary reason is the time–energy focus condition, which cannot be
preserved after every turn. Meanwhile, mass resolution (red circle in
Fig. 9) shows a steady upward trend, it is increasing with the lap
number, except for a stagnation for the highest lap numbers. To maximize
the instrument’s performance, Δt must be controlled.
Fig. 9. Measured Δt and resolution of133Cs+ions as a function of the number of laps performed in the MRTOF-MS.
Fig. 10 shows an example of a TOF peak of Cs+ ions
with the fitting function. The TOF peaks were fitted with a Gauss
function to obtain the mean TOF and their uncertainties. A mass
resolution of up to R FWHM = 116,050 for
Cs+ is achieved after 600 laps of reflection,
corresponding to a flight distance of about 1.08 km and a TOF of about
18.02 ms, with an FWHM of 77.65 ns.
Fig. 10. Mass spectrum of 133Cs+ions for 600 laps measured by API-MRTOF-MS. The red curves
are the fitted results with a Gaussian function, demonstrating the mass
resolution R FWHM = 116,050. The peak width refers
to the FWHM.
CONCLUSION
An API-MRTOF-MS was built and tested
with an ESI source. A resolution of R FWHM =
116,000 was achieved with an extremely short measurement time at the
millisecond level. The performance demonstrates that the API-MRTOF-MS,
with its fast analysis speed and high selectivity, is especially
suitable for high-resolution process analysis. This achievement
will facilitate the implementation of
API-MRTOF-MS in various scientific fields, such as the
analysis of transient processes in
chemistry, biology, and medicine, and will therefore promote the rapid
growth of these disciplines.