BHT peak in every injection

We have an Agilent 7890B GC coupled with a 5977E MSD. When we first buy the instrument, in every injection we were having a huge BHT peak covering all of the chromatogram. The support engineers tried almost every thing and at last changed the inlet. After 5 years of use we started the same problem. This time BHT is not covering the chromatogram, it is only a peak. When method parametres changed, the peak shape and retention time changes. Therefore I thought it was not comming from the Helium. Multiple injections of the same solution (even blank hexane) have BHT peaks, in the same RT but with different altitues. Sometimes it is a peak, sometimes a planar height but RT is always the same. When I checked the same solution with another equipment, no BHT.

I changed septa, liners and injectors millions of times.I changed washer and gold ring multiple times. I put a oxygen/water trap between the instrument and the helium tube. I dismantled the split/splitless inlet and clean every part of it with isopopyl alcohol and other solvents. I washed and cleaned the split vent valve tubing. But BHT is always there. Changing peak shapes and heights, but in the same RT (if method, flow, temp cahnges RT changes).

Because of BHT splitless injection and low concentration analysis is totaly imposible. In split injection, we have the BHT.

I gently want to ask you if anyone experienced the same problem.

We analyse essential oils diluted in hexane in split mode and sythetic markers in splitless mode. No BHT ever entered our lab.

Thanks in advance

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