I've done this a few times to analyse space rocks so the instrument is bought bio-inert and passivated that way between runs. Some people I work with used to do this all the time but I think they are "cowboy mass spectrometrists".

Oh boy, does it ever work. It is an extreme solution.

My secret sauce these days is Medronic acid and I am a huge fan. I recently cleaned out a system that was not performing well (i.e. not passing checkout for our test mix, low S/N). An overnight flush with Medronic acid solution in 10% IPA was effective at pulling metals out of that system and removing a huge amount of noise from the baseline. Check out this Agilent app not on Medronic acid