4.2 Performance of the API-MRTOF-MS
4.2.1 Signal intensity varying with lap numbers
Signal degradation over a long flight time is inevitable due to collisions of ions with the residual gas inside the analyzer, which is crucial for multicycle flight. About 10 ppm methanol solution of CsI was used to investigate the characteristics of signal variation with increasing flight distance. The ESI worked in a positive mode.
Fig. 7 shows the measured intensity at different laps. The signal is not stable for the first few laps, which can be attributed to the part of the ions not matching the phase-space acceptance of the analyzer (see also the corresponding response for the TOF distribution Δt in Fig. 9). Then, the signal suffers from a monotonic slow decay with increasing flight length. For the current situation, the transmission of the ions over 600 revolutions is about 50%, with a course of the order of 1.2 km.
Fig. 7. Signal intensity of 133Cs+ions as a function of the number of laps performed in the API-MRTOF-MS. At the highest lap number 667, the ions’ flight length is 1.2 km, and the corresponding time-of-flight is 20 ms.