I have an electrospray ionization capillary tip that sprays into a chamber that contains some circuit boards. An aqueous CsI sample is apparently causing a white residue to build up on these boards after some time. I thought the residue was the salt itself, but I can't dissolve it with water. I tried methanol and that didn't work either. Does anyone know what this could be and how to clean it? I'm worried about excess build up over time.

I considered that it might be CsOH, but that should also rinse away with water because its so soluble.

  • $\begingroup$ Most likely impurities in the water, although some soft glasses can dissolve a bit in water (cactus,maize and some sponges reinforce their structure from dissolved silica). How pure is the water you use? Are any cleaning material residues left in the apparatus? $\endgroup$ – DrMoishe Pippik Apr 25 '19 at 23:01
  • $\begingroup$ @DrMoishePippik - The water used is millipore water. However, the syringe has contained R6G before. it was rinsed and sonicated with MeOH thoroughly. $\endgroup$ – AnonymousGraduateStudent Apr 26 '19 at 17:05
  • $\begingroup$ Millipore have various devices. What is the level of dissolved solids?? $\endgroup$ – DrMoishe Pippik Apr 26 '19 at 18:12
  • $\begingroup$ @DrMoishePippik - This is 18 Mohm millipore and we are using mM levels of CsI. When we use something other than CsI we don't get this build-up, so I'm pretty sure it's related to the CsI somehow. Also some relevant information that I omitted before by mistake: these boards are gold-plated, and as I understand it there may be an alloy forming? As for cleaning materials, I have only used water and MeOH, with some rubbing with a cotton cleaning tip. $\endgroup$ – AnonymousGraduateStudent Apr 26 '19 at 19:06
  • $\begingroup$ Then I'd look to possible contamination in the CsI. Put a few drops of the plain conductivity water and a few drops of CsI solution on clean microscope slides and evaporate in a desiccator, then wash the slides with water and MeOH as you normally do. There should be no resdue. $\endgroup$ – DrMoishe Pippik Apr 26 '19 at 21:08

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