The solvolytic cleavage of octadecyl ligands from the surface of RP-18-type stationary phases in TLC. Part 2. Characterization by Raman spectroscopy

This study is a continuation of previous efforts aimed at establishing a si mple yet reliable method for quantification of the amount of solvolytic cle avage of octadecyl ligands from the surface of RP-18 TLC stationary phases under the influence of the strongly acidic or strongly basic mixed mobile p hases comprising methanol, water, and a suitable buffer solution (pH either 3 or 9). Our current experiment has exploited a Raman spectrometer, equipp ed with a high-power neodymium laser, to induce some astonishingly unusual effects (most probably dehydrogenation of the octadecyl ligands followed by least partial aromatization). This supposition is founded on the appearanc e, in the 2285 to 1130 cm(-1) region of the Raman spectra obtained from oct adecylmethylsiliceous (and several other organosiliceous) chemically bonded TLC stationary phases, of a very intense, broad, and highly structured spe ctral band typical of aromatic compounds. Quantification of the diminishing area under this particular spectroscopic band results in an immediate quan titative conclusion about the extent of solvolytic cleavage of the octadecy l ligands investigated. The results obtained were compared with those origi nating from two other analytical techniques, and relevant conclusions were drawn.