Here we have a method for analysing solvents in our GCMS 8860 / 5977B With an ALS G4567A
Our method consists of 27 compounds.
In our recent run we notice a drop in internal standard response Figure 1, in the middle of the run, and after signal return to normal. so it was not a matter of vial running out of IS.
During our investigation we notice that, especially for the samples affected, there was some retention time shifts on the first few minutes of the run. Figure 2 ( all these peaks should be the same RT)
These retention time shifts are visibly happening to around 3.4 min into the run.
Although the rest of the peaks in the 15 min run have the expected retention time, we are wondering if these shift is what is affecting signal for Internal standard.(figure 3)
Does anyone know wha could be causing such retention time shifts in the beggining of the run?