Does Electrospray ionization produce gas-phase or liquid-phase structures?

Electrospray ionization of tyrosine from a 3:1 (v:v) CH(3)OH/H(2)O solution is found to afford an M - H ion which is a 70:30 mixture of phenoxide and carboxylate ions. This corresponds to the gas-phase equilibrium composition and not the liquid-phase proportions. In contrast the carboxylate is produced as the dominant ion (similar to 95%) from anhydrous CH(3)CN and CH(3)CN/H(2)O mixtures. The addition of small amounts of CH(3)OH to the solvent, however, convert the M - H ion back into the gas-phase isomeric ratio. The isomeric structure therefore depends on the solvent system from which an ion is sprayed.