We are having issues with our PBDE method on GC-MSMS. We had a method developed using applications from Agilent for GC and MSMS conditions. When we run linearity, it seems our surrogates and/or internal standards increase in concentration as the native standard concentration increases (like a linear correlation) when they are all added at the same level. This effect occurs with the higher massed analytes, primarily Octa, Nona and Deca-BDE.

We have tried manufactured standards, making our own from serial dilution, different columns, different injection volumes and sandwiched techniques. 

The current method uses a pulsed spitless injection with gradient temperature in the MMI. When we tried a splitless technique or isocratic MMI we could not see BDE-209 (deca).

  • Hello,

    Seeing creeping internal standards means your standards may be sticking to your source.  So my first question is what is your source temperature?  We may need to increase the temp.

    A common fix to the creeping internal standard problem is to move to the 6mm or 9mm extraction lens.  I will link part numbers below.  I suggest you go to the 9mm as we have this same problem with PAHs and the 9mm fixes the issues.  However there is a tradeoff when you open the extraction lens aperture.  So there may be merit in first testing the 6mm then testing the 9mm.  The larger the aperture, the lower the resonance time for ionization.  So you may lose some sensitivity using the larger apertures.  Overall you will need to go to either the 6mm or the 9mm lens.  Its just a question of how big of a tradeoff in sensitivity you want to make.

    6mm Lens - G3870-20448 | Agilent

    9mm Lens - G3870-20449 | Agilent  

  • Thanks.

    We noticed a minor creep with the PAH as well but nothing significant.

    The PBDE was run using 280C primarily since many app notes use it (quads 150C). I did try 300C the other day and had the same issue - std 5 was about 3x higher than std 2 for mass labeled at same concentration.

    We may just be changing the calibration curve to suit our purposes. We were hoping to use purchased, prepared but isn't seeming likely. The range is quite drastic for some of the higher compounds (5-5000 ng/mL for nona- and deca-BDE, 500 ng/mL mass-labeled of the same).

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