Sm. Blair et al., Evaluation of binding selectivities of caged crown ligands toward heavy metals by electrospray ionization/quadrupole ion trap mass spectrometry, ANALYT CHEM, 72(11), 2000, pp. 2433-2445
Electrospray ionization (ESI)/quadrupole ion trap mass spectrometry is used
to evaluate the heavy metal binding selectivities of five caged crown ethe
rs and two polyether reference compounds in methanol solution. The binding
preferences for Hg2+, Pb2+, Cd2+, and Cu2+ were analyzed by comparison of E
SI mass spectral intensities with the aim of developing this method for the
rapid screening of binding selectivities of new synthetic ligands, The cag
e compounds preferentially bind Hg2+, except for the cage cryptand derivati
ve, which favors Pb2+, The preference for Hg2+ stems from the favorable pos
itioning of the nitrogen or sulfur atoms for linear coordination of Hg2+, w
hereas the cryptand derivative favors Pb2+ because of its larger cavity siz
e. The counterions of the metal salts influence the type of complexes obser
ved in the ESI mass spectra because the strengths of the metal-anion bonds
affect retention of the anion in the complexes.