Siloxane Peaks in Total Ion Chromatogram (TIC)

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    Siloxane peaks in a Total Ion Chromatogram (TIC) are a characteristic pattern of masses 73,147,221,281 and 313

    When confronted with a number of siloxane peaks as typically seen in the attached PDF, consider where they can logically come from. Poly-siloxanes only exist where some form of surface deactivation has occurred:

    1. Injection port liner
    2. Column
    3. Sample vials
    4. Extraction tubes

     

    To narrow down the choices, run an oven blank. If the peaks persist you can rule out items 3 & 4

     

    This means some of the deactivation on the liner and or column is failing. Since columns cannot generate peaks from the stationary phase, one must deduce that the liner is losing its deactivation and the column is simply chromatographing these random siloxanes.

     

    The primary cause of this phenomenon is the presence of water in the carrier gas. Traps in the helium line that have become saturated due to age, or new traps that have been improperly manufactured/installed, can be the source of sufficient water capable of causing this kind of breakdown in the liner.

     

    Remove the trap and bake the system dry. Install a new liner and observe the behavior. The unwanted siloxane peaks should diminish within a fairly short period of time.

     

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