Yes, there is some small peaks that elute at high temperature. Being not a specialist in mass spectrometry, it is still visible by the mass spectra that those compounds contain bromide. When at first perylene disappear, the recovery for pentachlorophenol-c13 was good. Last week, because of high noise (mostly column bleed) I concentrated my extract to 200µl instead of 500µl. When I did the integration, I noticed that perylene totally disappear but also that pentachlorophenol-c13 recovery was very high. We use as internal standard for pentachlorophenol 2,4,6-Tribromophenol. Now, the 2,4,6-Tribromophenol recovery is very low, putting high the recovery of pentachlorophenol-c13. It seems that there is a chemical reaction between 2,4,6-tribromophenol and perylene-d12, but only in the extracts and not in the standards.