Yellowing of 1,2,4-trichlorobenzene

[DRFournier5]

I have been using anhydrous 1,2,4-trichlorobenzene in our high temperature GPC for a few years now, using BHT as an added antioxidant. Lately I have noticed that the clean recycled solvent (which recirculates through the system at 140C) has been turning a bit yellow. Everything chromatography-wise appears normal. I spoke with a service engineer who was not at all surprised at the yellowing of the solvent, though it seems strange that it would have not done this for a few years. The BHT is probably 6 years old or so at this point.

The solvent bottle has been replaced by a brand new one and it has been proven that it is not polymer that has accidentally gone into the clean solvent bottle, as we have to manually change the tubing to go to waste when running a sample.

If anyone has any thoughts, questions or experience with this, it would be reassuring to know if this is okay or if there is something about the system (column, guard, etc) that may be causing this.

Also, the solvent directly from the bottle appears colorless as it normally would.

[prepcolumn]

DRFournier5,
at first glance it seems like oxidation of BHT somehow. BHT possibly oxidize to quinone and green/yellow colors are the typical colors of quinones.