Cleaning a stubborn Electrospray residue

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.


