CRITICAL REEVALUATION OF FABMS ANALYSIS OF LIGAND CATION INTERACTIONS

Whilst the use of FABMS in the analysis of ligand-cation interactions has become widespread, there are a number of experimental variables as sociated with the use of this technique, the effects of which have not previously been addressed. The interactions of 12-crown-4, 15-crown-5 and 18-crown-6 with the alkali metal cations reveal two important obs ervations: (i) that the matrix employed for the FAB studies has a dram atic effect on the observed binding behaviour and (ii) that the observ ed relative intensities of protonated ions ([M + H](+)) and metallated ions ([M + Metal](+)) differ enormously. Determination of the ratios Of these signals would allow quantitative arguments to be applied to e xperiments of this type. Accordingly, previous reports of the use of F ABMS for the quantitative study of ligand-cation interactions must be viewed with caution.