On my D7890B GC I am running test method D5580 for benzene, toluene and total aromatics. A new column was installed about two months following poor quanitifcation of compounds such as benzene and toluene. It has been running smoothly since. However, this week I have begun noticing my benzene content has dropped. I was averaging a 0.55 wt% and now I am down to 0.27% on my QC samples. Other samples have also shown a reduction in the content by almost half. Ethylbenzene is also starting to slowly fade. Any advice as to what may be occurring?