Using Ammonium Formate in my mobile phase but it is coating my spray chamber and possibly causing suppression. Mitigation strategies?

Hi all! Through much troubleshooting, I have determined that the white powder that is coating the spray chamber of my MS is the ammonium formate that is in my mobile phase. I started developing an amino acid method and the recommended mobile phase was 20mM ammonium formate at pH 3. It is a gradient method so I am using 20mM ammonium formate in water and in ACN. I have tried lowering the concentration of AF to 5mM but I am still seeing the powder, though much less. I am wondering if you all have suggestions for mitigating. Is it possible the temperature is too high and instead of just aspirating it into smaller droplets, it is vaporizing and drying before it can get to the capillary tube? I am also seeing diminished signal of my reference ions so I am concerned this is also causing suppression. Any suggestions would be helpful. I attached a photo so you know what I am dealing with.
Thanks!
Katy
  • What HPLC column are you using?  What reagent did you use to lower the pH?  What are your source conditions and HPLC flow rate?

  • I am using an InfinityLab Poroshell 120 HILIC-Z.  For pH adjustment, 0.2N HCl.  Source conditions (if I understand what you mean) are ESI with a flow rate of 0.5mL/min.  

  • Hi Katy,

    Looks like you are coating the spray chamber with ammonium chloride, not ammonium format.  I wouldn't recommend using HCl to reduce the pH of your ammonium formate.  Adjust the pH with formic acid instead, and he problem should go away.

    Kind regards

    Andy

  • I think Andy's right (pun intended). I've seen this a couple times before where insoluble salts were formed when adjusting pH. 

    I would probably recommend having your system cleaned/PM'd if you are able to. Last time this happened, it made it all the way back to the quads. 

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