Raman spectroscopic quantification of the extent of hydrolytic cleavage ofoctyl ligands from the surface of RP-8-type stationary phases in TLC with mobile phase buffers of pH from 1 to 10

This is the fourth paper in a series reporting a study of the susceptibilit y of selected chemically bonded stationary phases used in thin-layer chroma tography to hydrolytic cleavage of the organic ligands from the surface of the silica matrix. The uniqueness of this approach consists in a pioneer ap plication of Raman spectroscopy (and more specifically in the use of a high -power neodymium (Nd:WVO4) laser) for quantification of this chemically ind uced destruction process, which has a considerable negative impact on perfo rmance of the chromatographic system. Our three previous papers described the use of high-power laser Raman spect roscopy to scrutinize the susceptibility of TLC-type chemically bonded octa decyl stationary phases to hydrolytic cleavage of the octadecyl ligands fro m the silica matrix surface. It was established that the extent of cleavage was always similar (in practice ca 20 %), irrespective of the pH of the mo bile phase employed. In this paper we report the results of a fully analogous Raman spectroscopi c study; the only difference is that this time we have investigated the sus ceptibility of octyl (not octadecyl) chemically bonded stationary phases to hydrolytic cleavage. For this stationary phase the extent of cleavage prov ed markedly ps-dependent - for acidic mobile phases (i.e. relatively low pH values) the amount of cleavage approached 100% whereas for basic mobile ph ases (i.e. relatively high pH values) the amount of cleavage never exceeded 20%.