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

  • Thank you so much for your assistance.I am sharing the spectrum of the compound.

    On the other hand cold-trapping is not neccessary for us. We checked all the columns in another system and faced no BHT.

    The last part I didn't replace is the split vent trap. I ordered the part but I don't thing it causes this issue.

    As I mentioned earlier, when we first installed the instrument in our lab it had  the same problem with much more BHT in the inlet. And of cource the trap was just installed.

  • Solved the problem. My tune report today ended up with 18.75% nitrogen and 0.3% oxygen. Waited for a few hours and it became worse. I wrench tightened every nut in the instrument and found out a leakage at the carrier gas inlet of oxygen/water trap. After fixing it, nitrogen level droped drastically to 0.8%. The trap was trapping oxygen for sure but not nitrogen. After a few blank hexane injections, BHT totally disappered. Now, even in splitless mode, system is BHT free. But I really don’t know how a leakage resulted a BHT (or a spectrum similar to BHT) contamination which only appears in injections and giving a peak.

  • That's right, there is not a trap that captures nitrogen.  You may want to purchase an electronic leak detector.

    That spectrum is more than likely column bleed, which happens when the cross-linked spine of the stationary phase is broken by oxidation and heat. 

    Glad it's working better now.

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