Gj. Vanberkel et al., CHANGES IN BULK SOLUTION PH CAUSED BY THE INHERENT CONTROLLED-CURRENTELECTROLYTIC PROCESS OF AN ELECTROSPRAY ION-SOURCE, International journal of mass spectrometry and ion processes, 162(1-3), 1997, pp. 55-67
Citations number
40
Categorie Soggetti
Spectroscopy,"Physics, Atomic, Molecular & Chemical
The redox reactions that take place in the metal capillary of an elect
rospray ion source to maintain charge balance alter the composition of
the initial solution entering the capillary. Data presented here demo
nstrate that under certain ES conditions, solution pH may be decreased
significantly (by at least 4 pH units) as a result of the electrolyti
c oxidation of water in positive ion mode electrospray-mass spectromet
ry (ES-MS). Furthermore, it is shown that this pH change can have an a
ffect on the appearance of the ES mass spectrum of an of analyte. An E
S ion source in which the pH of an indicator solution exiting the capi
llary is monitored optically, before the spraying process, is used to
demonstrate that electrolytic reactions in positive ion mode ES can de
crease the pH of the initial solution. ES-MS studies using bovine hear
t cytochrome c are used to illustrate the influence of the electrolyti
cally-induced pH change on the gas-phase ion signals for the multiply
protonated protein. The magnitude of electrolytically-induced changes
in solution pH will be most significant in non-buffered solutions near
neutral pH when using metal spray capillaries or metal contacts to so
lution comprised of difficult to oxidize material (e.g. platinum or go
ld), Any pH changes will increase in magnitude as the flow rate decrea
ses and/or ES current increases (all other ES parameters constant). Th
erefore, the potential impact of these redox reactions in ES-MS, if an
y, will probably be most important in the very low flow rate ES-MS sys
tems (less than or equal to 1.0 mu L min(-1)). (C) 1997 Elsevier Scien
ce B.V.