Peruvian salt mines, seaside rust, HPLC precipitates and electrospray ionization – gas-phase ionic solids: is it all the same?

I enjoy very much the history behind the science. When reading the lecture about the Electrospray Nobel prize of 2002 from John Fenn: Electrospray wings for molecular elephants, that I start to note how a similar effect surround me and I never noted. In this lecture Fenn said that in 1976 two meteorologists were doing research on something they called “Atmospheric Pressure Ion Evaporation”, a kind of precursor of actual electrospray Ionization for mass spectrometers. The goal was to investigate “the possibility that charged droplets of sea water might be a source of some of the ions found in the atmosphere”.

Interesting, so we can have ionic salts on atmosphere? I never knew about that. Hmmm, so that’s why on seaside things seems to rust more easily, the “Maresia” effect (sorry, couldn’t really found a English word for that!!).

During a trip to Peru I visited a salt mine (not really a mine), where Peruvians directed a stream of salted water that came from a mountain to “pools” where it was dry out and the salt recovered.
The region was dry, few rainy days per year. But all place was covered with salt, I exclude the possibility of spills during rain for the reason I just described. The only possibility I see is salt carried by micro droplets during evaporation. You can see a photo at left.

Last month after my vacations I came back to work and saw some crystals growing from connection on HPLC (left), outside and inside the oven. No one had a previously leaking, the crystals came from the thin film of mobile phase from connections. Time was passing and during drying out the solvent carried the salt buffers over the metal. This explains how the salt covered the metal surface without a visible leaking but don’t explain how the mobile-phase evaporated so much without we see any leaking. By the way, we have leaking detector on ovens, and they work.

Anyone out there already did a 30% NaOH solution out a hood? Did you smell anything? Well, it seems that ionic solids are not so not-volatile as they taught to us…I think it follow that universal answer on chromatography: It depends of…

Almost the same principle is applied to Electrospray Ionization interface for mass spectrometers (left). But in this case the substance you want to analyse is ionized (with charge)and the equipment applies some potential to make the drop literally explode, they call coulombic explosion. And then, the ion free of solvent can be weighted using a magnetic field.

Last photo: Agilent Technologies.