DETERMINATION OF BINDING SELECTIVITIES IN HOST-GUEST COMPLEXATION BY ELECTROSPRAY QUADRUPOLE ION-TRAP MASS-SPECTROMETRY/

The quantifiable relationship between the equilibrium solution composi tion and electrospray (ESI) mass spectral peak intensities of simple h ost-guest complexes was investigated. Specifically, host-guest complex es of simple crown ethers or glymes with alkali metals and ammonium io ns were studied. Comparisons were made between the theoretical concent rations of host- guest complexes derived in solution from known stabil ity constants and the peak intensities for the complexes observed by E SI mass spectrometry (ESI-MS). Two types of complexation experiments w ere undertaken. First, complexation of a single guest ion, such as an alkali metal, and two crown ethers was studied to evaluate the determi nation of binding selectivities. Second, complexation of two different guest ions by a single polyether host was also examined. In general, solvation was found to play an integral part in the ability to quantif y binding selectivities by ESI-MS. The more similar the solvation ener gies of the two complexes in the mixture, the more quantifiable their binding selectivities by ESI-MS. Ln some cases, excellent correlation was obtained between the theoretically predicted selectivity ratios an d the ESI mass spectral ratios, in particular when the ESI ratios were adjusted based on evaluation of ESI response factors for the various host- guest complexes. (C) 1998 American society for Mass Spectrometry .