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

twitsok

Hello,

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?

  • 0 in reply to twitsok

    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?

  • 0 in reply to glafosca

    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%.

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