Tailing problem during PAH's analysis. GC/MS 7820A/5977E

Hello everyone,

Our system is 7820A/5977E we have a tailing problem during PAH's analysis.

The method we used is:

Injection Volume: 1 µl

55 C held for 5 min, 25 C/min to 320 C, held for 3 min

Carrier gas: He 1.5 ml/min

Column: HP 5: 30m x 0,25 mm x 0,25 µm

Liner: 4mm id, dual taper deactivated, no wool

Mode: P.Splitless

Acquisition mode: EI, SIM (1 to 200 pg)

Aux: 290 C, Ions Source:340 C, MS Quad: 150 C

What we made until now is:

Cleaning the Inlet and the ion source, using different Liners. increase Transfer line temperature to 340 C. Change the column, new pre, and post-column, Septa and O-Ring, different solvents, bake out the MSD, and different PAHs standards.


Air/Water check:

18/69 = 0.59 Water% (counts=5538)

28/69 = 2.36 Nitrogen% (counts=22200)

32/69 = 1.29 Oxygen% (counts=12140)

44/69 = 0.17 Carbon Dioxide% (counts=1586)



Any comments and suggestions will be appreciated

Parents Reply
  • Hello ,

    It could be both, but if you are seeing tailing problemas also with standars it suggests to be more likely an instrument issue. Since you already trimmed the column and re installed it, looks like everything is checked. How did you clean the injector? This clean helped at all?

    Do you run any other methods in this GC to compare, in addition to alkan standards?

    If everything was checked and its OK, I still continue to suggest to evaluate an UI column. I know many cases the HP-5 could work but it depends on PAH concentration, types of PAHs, your matrix and other individual parameters from each application to determine if the inertness is enough or not. Maybe this is one of the situations where each detail in the instrument and in the column will help you to get more symetric peaks.

    Thank you

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