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.