Investigation of Alkali Metal Cation Selectivities of Lariat Ethers by Electrospray Ionization Mass Spectrometry

The alkali metal ion selectivities of several dibenzo-16-crown-5 lariat ethers are investigated by electrospray ionization mass spectrometry (ESIMS). Specifically, the mass spectral peak intensities of lariat ether/alkali metal cation complexes obtained by electrospray ionization of solutions containing each lariat ether with lithium, sodium, and potassium salts are compared. The relative intensities of peaks for the lariat ether/alkali metal cation complexes indicate the metal-ion selectivities of the lariat ethers. A series of dibenzo-16-crown-5 lariat ethers containing methoxy, carboxylic acid, ester, or amide pendant groups is studied in this fashion. A majority of these lariat ethers studied are found to be selective for Na+ vs either Li+ or K+ in methanolic solution. The selectivities obtained by the electrospray mass spectrometric method are compared with reported selectivities obtained by potentiometric methods with solvent polymeric membrane electrodes.