Beneficial effect of macrocyclic ligands on field desorption mass spectra of samples containing alkali metal ions

Addition of a macrocyclic ligand, such as a crown ether or cryptate, to the solution of an organic compound containing alkali metal ions prior to field desorption mass spectral analysis, has been shown to result in a reproducible, smooth field desorption process at low anode temperature. Crystalline dibenzo-18-crown-6 ether complexes of NaI and KI give field desorption spectra in which free and complexed ligands are of comparable intensity. Cryptate complexes retain the metal ion even more strongly, as illustrated by the fact that the complex of LiCl with [2.1.1]-cryptate yields almost exclusively the complexed lithium peak on field desorption. Alkali metal salts with organic anions also desorb more smoothly after complexation, although in the case of simple carboxylates the anion is found only in a cluster peak.