We cleaned the ion source, cut the column, changed the inlet from front to back (because the front inlet has some issue). After these maintenances, the tune file looks good, the ion abundance in tune file is similar as before. However, low TIC was observed with 1uL injection of our samples, with about 0.2 relative abundance compared to before. And we tried to inject 5 uL to increase the signal, however, the TIC didn't improve significantly. The results obtained can go forward but we want to know what is the reason here. Does anyone meet similar issue? Thanks.