INFLUENCE OF ALKYL CHAIN-LENGTH ON THE STABILITY OF NORMAL-ALKYL-MODIFIED REVERSED PHASES .2. MODEL DISSOLUTION STUDY

A direct, in situ study of the hydrolysis and dissolution of various n -alkyl modified phases was performed with 29Si magic angle spinning NMR spectrometry as a model for stationary phase aging In laboratory practice. With this study, the substantial effect of the ligand length on the dissolution reaction of the alkyi modified phases under aggressive eluent conditions is confirmed. As expected, longer n-alkyl ligands gradually show better substrate shielding properties. Above a certain critical ligand length, shielding by longer ligands inhibit the dissolution rate drastically by affecting the hydrolysis and dissolution processes. The type of solvent system used, In liquid chromatography practice or for dissolution studies as reported here, mainly affects the proportions of dissolved silicates In the eluent. On the basis of this in situ dissolution study a model for ligand and substrate hydrolysis and dissolution with the involved reactions is presented. © 1990, American Chemical Society. All rights reserved.