CORRELATION BETWEEN SOLVATION ENERGIES AND ELECTROSPRAY MASS-SPECTROMETRIC RESPONSE FACTORS - STUDY BY ELECTROSPRAY MASS-SPECTROMETRY OF SUPRAMOLECULAR COMPLEXES IN THERMODYNAMIC-EQUILIBRIUM IN SOLUTION

Electrospray mass spectrometric (ESMS) studies of solutions of alkali metal chlorides have shown that the value of the solvation energy is a key parameter in the ion yield in ESMS. The ESMS response factor, k(M ), of the ion is linked to the solvation energy, E(M), of the ion by a simple mathematical relationship, k(M) = C exp(-0.015 E(M)), where C is a constant depending on the ion charge, the ion concentration and t he instrument parameters. In two competition experiments, the relative affinities of Na+, K+, Rb+ and Cs+ for the cryptate 222 and for the c rown ether 18C6 were directly deduced from the ES mass spectrum. This result opens up the possibility of direct quantification studies by ES MS of molecular species present in thermodynamic equilibrium in soluti on, and also a better understanding of the ES process.