Hello, during our multi residue pesticides analysis of our usual QC, we started to notice that certain compounds started disappearing. The runs are around 17 min, and the missing compounds are all in the time frame 10-12 min. This happening is inconsistent, as it could be in the morning run they would be there, and later in the day reappear, or they would disappear for several days, see weeks. Are there any suggestions why would this inconsistency be happening, and only in a small time window? We're using an LC-MS system 1290 infinity II LC system +G6495C triple quad.
We've already checked both the sprayer and the transfer capillary, and even tried replacing them, but the problem is still there.