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

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 (agilent.com): 

5989_5672.qxd (agilent.com)

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?

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

Since you are using a different column for PBDE, the PAH chromatography shouldn't be affected. I guess you change liner accordingly, as well of cleaning the inside of the Inlet with solvent-q-tip to keep the sample injection part clean as possible. What Liner are you using: 4 mm ID ultra inert with glass wool on the bottom? Have you ever tried the dimpled liner 5190-2296? What's your injection volume?

1 uL is injected for PAH. 

We do change the liner often and are using the one from all the app notes (with glass wool). We haven't tried a dimpled but do use a dimpled with the PBDE method. 

After doing a bunch of troubleshooting over the last few weeks we thought we had the return of the surrogates but then ran a batch and had the same situation, low recoveries for the surrogates for final analytes. The area counts for the internal standards looked similar but the surrogates were closer to 10% suppressed (extracted compared to the neat standards). The peaks had improved though and are no longer in the noise but they are still low recoveries. Dilution (1/20) did improve the recoveries from <10% to about 60%.