Raman spectroscopic quantification of the extent of hydrolytic cleavage oforganic ligands from the surface of CN- and diol-type stationary phases inTLC with mobile phase buffers of pH from 1 to 10

In this paper we present results from our most recent investigations on the susceptibility of CN- and diol-type TLC stationary phases to hydrolytic cl eavage of the 3-cyanopropyl and diol ligands from the silica matrix surface . Again, hydrolytic cleavage was induced by use of mobile phases comprising mixtures of methanol, water and the buffers of different pH; high-power ne odymium laser Raman spectroscopy was employed as a quantification tool. It was established that CN- and diol-type polar ligands are less susceptible t o hydrolytic cleavage than apolar (C-8 and C-18) ligands. This quite unexpe cted and even striking difference between the two types of stationary phase can probably be explained by use of an ion-exclusion mechanism (because of the formation of the Donnan membrane potential on the solid-liquid interfa ce), which occurs for polar ligands and protects them from immediate contac t with ions originating from the buffers.