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.