Injection valve contamination on LC-QTOF

I have been tracking down this big source of contamination for a while now, and I think I've got at least part of it figured out. I would love to hear some other thoughts or solutions.

Below are replicate injections of LC-MS grade methanol loaded into a vial. There is no column installed. LC flow is 0.075 mL/min LC-MS grade methanol. Ion source is a Dual AJS on a 6560 IM-Q-ToF in low mass mode (m/z 1700, 2 GHz, Ext Dyn Range). The LC is a 1290 Infinity with a quaternary pump and single-needle multisampler. The system is < 1 yr old and does not get very heavy use (at least not yet).

The peak at -8.75 mins appears after changing from mainpass to bypass on the injection valve. Peaks at roughly -8 mins and -7 mins appear after going from bypass to mainpass with the injection valve. No injections were performed.

Injections can be seen at -4.5 mins and 0 mins on the time scale. These are the blank MeOH injections. 

Here are some mass spectra corresponding to the three peaks from the first MeOH injection. At some points in the injection (slightly off of the TIC peaks) I can pretty clearly identify polysiloxanes and perhaps also propylene glycol repeating units. In these spectra, there are some signatures of phthalates, and these prominent peaks at m/z 360. 

It appears to me that the injection valve is having at least something to do with the contamination we are seeing. Perhaps there is another source as well.  I have replaced the injection valve rotor seal already, and these data came after that replacement. In fact, I even opened the valve up a second time and thoroughly cleaned the stator and rotor seal again today before all of this. Not seeing big improvements, but this contamination only comes up when an injection is made or when the injector is actuated.

Any thoughts?

  • Hi,

    Contamination could be in the needle, seat, or loop. Best way to get rid ppg and flush hot water through the contaminated module(s).

  • Thanks - I'll try hot water. 

    I've replaced the needle seat with a brand new one, no changes. Replaced the rotor seal, no changes. I don't see any of this contamination when in main pass, except when the injection valve is actuated, so I'm hesitant to blame the needle and loop, but it's possible I guess. I've cleaned the outside of the needle. I have also verified that it is not related to the septum in the vial cap, as I've removed some of them and still see this same thing.

  • Hi,

    With the ipa you put in the vials, write a sequence containing 30-40 injections with the full volume of the loop. 
    analysis time can be 1 min. So you can clear the loop. please don't forget the remove the column during the sequence.
  • I ended up cleaning the whole system thoroughly with a bunch of different solvents, including the HPLC flushing solvent that shipped with the instrument, Waters Magic Mix, hot water... all sorts of things. Mostly I've just been discovering that I think most of our solvents are contaminated with something or other. It's amazing actually how quickly things are getting contaminated. I finally found a truly clean bottle of ACN and one specific DI system that is cleaner than the rest. I think with enough injections and cleaning it started to go away... but I think I've found just about every contaminant in the book on the way there. Still I think I'm suffering a sensitivity loss due to background so I need to find time to continue cleaning this all up... 

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