PAH loss of mass-labelled standards GC-MS/MS


I have always had such wonderful help here.

We are currently running PAH in smoked fish using mass-labelled C13 standards and a MgSO4/NaCl with silica column cleanup on a 7010 GC-MS/MS.

The standards are solvent and we are having issues with the higher boiling ones -Indeno, benzo[ghi], dibenzopyrenes...

SInce validation, we have lost the areas of our surrogates, they cannot be found unless we dilute. We have had a PM, tried another column, changed numerous liner, septas and syringes and cannot rectify. The mass spec appears to have sensitivity but it seems the matric is now interfering when it had not before (since dilution helps). 

Any suggestions?

  • What kind of fish are you testing? It can be related to the fat content. Have you ever tried the EMR-Lipid polish tube or cartridge? See applications below.

    Determination of 19 Polycyclic Aromatic Hydrocarbon Compounds in Salmon and Beef (

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  • We are testing smoked fish, mostly herring and salmon. During validation we tested non-smoked products: salmon herring, shrimp, oysters.

    We haven't tried another type of QuEChERs because this was actually an instrument transfer from a magnetic sector, so the extraction was already done years prior.

    But, since this question, we have gained back our high boilers. We had a PM done and re-injected with no improvement, did all the testing and some more and then re-injected and they are back. We have no idea what has changed. Our fear is that we have been starting to validate for PBDEs and they are causing an interference and since we haven't ran PBDE in a long time, the system got flushed out (?) 

    With all that though, we are exploring PBDE and may go back to trying QuEChERs again (we were having suppression there as well) and are looking in to the EMR-Lipid.

  • Are you using the same column to screen both PAHs and PBDEs? If yes which type of column are using?

    Are you testing Mono- up to DecaBDE?

    I assume you don’t have any backflush system installed, correct?

    What’s your current step-by-step extraction and purification procedure? 

  • Different columns.

    We are attempting to test for Mono-Deca but uncertain if we can get down to the Mono, Di depending on extraction chosen. When we were testing some different Quechers at the time, we couldn't see the internal standards that were added post-extraction (assumed matrix suppression).

    We are not backflushing, we are using a single column as well for both. When we tried the 2 columns for PAHs were were getting different retention times of some analytes compared to on the magnetic sector instrument. when using the PUU.

    For PAH - We add the surrogates (C13) standards then we extract with water and ethyl acetate then 2:1 MgSO4:NaCl. The aliquot removed is added to a prepared silica column (10 g activated with DCM, heat and sandwiched between Na2SO4) and eluted with 80:20 hexane: DCM. We evaporate down and reconstitute with internal standards (deuterated).

    When we were finding the method slowly deteriorating, dilution would help bring back some of the surrogates. Throughout the process, everything was also running fine on the magnetic sector.

  • The same extraction procedure should allow you have both PBDEs and PAHs in the final extract.

    What type of column and dimension?

    Do you have a SSL or MMI inlet?

  • Sorry for the delay.

    MMI is used for both methods, pulsed splitless with a temperature ramp.

    PAH - 30 meter, Rxi-17Sil (Restek), 0.25 mm I.D., 0.25 μm film thickness

    PBDE - J&W Ultra 1 GC Column, 17 m, 0.20 mm, 0.11 µm

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