Abstract
Electrospray Ionization Mass Spectrometry (ESI/MS) has quickly become a versatile method of qualitative analysis of a wide variety of host–guest complexes formed in solution. However, considerable controversy exists on how ESI spectra quantitatively reflect and compare to the results obtained on these complexes. The extraction of alkali cations from acidic aqueous solutions by nine various calix[4]arenes-crown-6 diluted in NPOE, was studied by using ESI/MS. The stoichiometry of cesium complex and Cs+/Na+ selectivity were evaluated.