We report that the cesium salts of monobutyl phthalate, heptafluorobutyric
acid, tridecafluoroheptanoic acid, and perfluorosebacic acid generate salt/
cluster ions that provide calibration peaks for electrospray mass spectrome
ters. In the case of the cesium salt of tridecafluoroheptanoic acid ions ar
e available up to m/z 10,000. (C) 1999 American Society for Mass Spectromet
ry.