TQD contamination

<p>Hello!</p><p>I had a very noisy signal at the tune window in MS scan (e6-5, with a huge m/z 59 of intensity 4.0e7) with fluidics valve in waste. Intellistart instrument calibration yielded abnormal values, probably because of contamination. After thoroughly cleaning the source (ion block, cone, etc.; they didn´t seem so dirty), background signal was succesfully reduced to e3 (MS scan and valve in waste). But after infusing calibration solution (ICe-INa in MeOH) signal rise again and remain constant in e6 after hours in waste position (see below). I don´t think calibration solution is the problem, infusion lasted no mare than 10 minutes. Furthermore, signal does not decrease after switching fluidics to waste. Thank you!</p><p></p><p><img __jive_ID="1113" alt="tune.png" class="jive-image-thumbnail jive-image" onclick="" src="tune.png" width="450"/></p>


  • RD


    I'm hoping that by now, you have determined the source of your problem.

    If not, some questions and comments.

    1) Do you see m/z 59 if you infuse calibrant ?

    2) Are you using acetonitrile and and additive containing NH4+ ?  A common background adduct for that combination would be ACN+NH4 (41+18).


  • Hello,

    We contacted local technical service for an inspection. After cleaning the source and the hexapole, signal has improved a little bit, but there some kind of remaining contamination yielding low mass peaks (currently we have an annoying m/z 149!). Furthermore, there was something wrong with Masslynx v4.1. It may sound bizarre, but signal has changed a lot after reinstalling it and the TQD is working better.

    Thank you very much for your answer.

    PD: We do not use acetonitrile, but methanol.

  • Hi Eric,

    I would recommend flushing your fluidics with something like isopropyl alcohol. Purge several times through the system and also make sure the valve is being moved between LC, combined and infusion in case the valve itself. It is also worth making sure the ACQUITY has been flushed through. It's unlikely that it is the ACQUITY but it is always good idea to make sure it's clean. If you don't get anywhere please let me know.



  • Although I still have some remaining contamination in the TQD, it's been useful to flush it with isopropyl alcohol. Thank you!

  • Hi Eric,

    I have attached some documents, regarding contamination and how to minimize it, that I have found very useful, when struggling with background peaks or high background noise. Table 2 and 3 in the document "Controlling Contamination in UPLC_MS and HPLC_MS Systems.pdf" are worth a look. Just be sure to follow the instructions regarding disconnecting columns, MS detector etc.

    All documents are originally from the Waters webpage.

    Best regards


  • Thank you! It's a very useful information

    Best regards


  • Hi there,

    I wonder if you had/have an issue with your diverter valve on the front of your TQD. We have had a few instances of this valve actually becoming blocked and causing problems when we try to optimize the TQD. In these events we bypass this valve and use a separate syringe pump. I'd be curious to see if you still have this contamination when bypassing the valve. Best wishes, at any rate!

    Thank you,