Chromatography Forum

Hello,

I recently came across a paper describing using water clusters formed in ESI for mass axis calibration and was curious if anyone here has tried. (Ledmand & Fox, JASMS Water cluster calibration reduces mass error in electrospray ionization mass spectrometry of proteins, https://doi.org/10.1016/S1044-0305(97)00157-8)

We currently calibrate our QToF using sodium formate clusters. It works well, but it seems to push adduct formation to Na+ in the sample run after calibrating.

Has anyone tried it out? The TFA has me a little skittish about killing ESI(-) sensitivity which we may use in future.

Thanks!

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.