Determination of binding selectivities by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry is used for the measurement of bi nding selectivities of four model hosts, 18-crown-6, dibenzo-18-crown-6, di cyclohexano-18-crown-6, and 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, f or both alkali and transition metal ions. Based on the intensities of the m etal complexes observed in the mass spectra, the relative binding selectivi ties can be directly estimated. Results are compared to theoretical selecti vities obtained by solving simultaneous equilibria equations that define th e competing complexation reactions in solution. Good agreement is found in most cases, thus allowing rapid determination of binding selectivities of h osts in a variety of solvents.