by
lmh » Wed Apr 17, 2019 10:57 am
It's an interesting idea, do post back if you manage to get it to work! I am sceptical it will apply to modern instruments. I've never managed to see a beautiful water cluster spectrum as they show, even when I've selected excessive voltages in lenses near the spray chamber (which I've tried mostly when trying to induce source fragmentation) or when I've (accidentally) had far too much aqueous flow for the drying conditions. Usually on quadrupoles I've just seen a messy spectrum of random "masses" that actually correspond to droplets of "undesorbed" water flying through the instrument at random times.
This is quite an old reference. I suspect that instrument designers have put a lot of effort into making their spray chambers and ion optics as effective as possible at removing solvent (so that analysts can use high flows and still see clean backgrounds), so in trying to use water as a calibrant, you're fighting against the designers and their innovations. If it worked, it'd be lovely, as it can be difficult to find something that forms effective clusters at low mass in particular.
I share your concern about TFA, though I usually find that sensitivity returns fairly quickly once it's out of the system, provided it hasn't been used in enormous quantities.