Hello everyone. We've been experiencing an issue with our instrumentations recently where certain halogenated compounds (Freon-11, Freon-12, carbon tetrachloride, and 1,1,2,2-tetrachloroethane) seems to increase after calibration at a rate higher than the rest of our 78-compound list. We analyze whole air samples (TO-15) and use a preconcentrator to remove CO2 and water. The majority of our instruments are 6890/5973 GC-MS with a handful of 7890/5975's. We are seeing this across all instrumentation. We've checked carrier gas for contamination (as well as a hydrocarbon trap), we've changed transfer lines, great BFB checks. Preparing fresh standards has no effect. Thoughts?

Thanks so much.