Photoelectron spectroscopic study of the surfaces of some high-performance liquid chromatography substrates

Abstract

An X-ray photoelectron spectroscopic study of seven different substrates used in high-performance liquid chromatography is described. The substrates investigated are RP2, RP8, Permaphase ODS, Permaphase ETH, Spherisorb ODS, Spehrisorb-5-Amino and Spherisorb-5-Nitrile; in addition, and for comparative purposes only, core-level spectra have been obtained for samples of quartz and standard silica. Wide-scan spectra in the electron binding energy range (0 to ca. 1000 eV) provided a chemical characterisation of the respective “surface regions”, i.e., within a depth of ca. 20 Å. In addition to the anticipated photoelectron peaks owing to silicon, oxygen and carbon, clear evidence for the presence of sodium and titanium was obtained with some of the substrates. In the case of Spherisorb-5-Amino and Spherisorb-5-Nitrile high resolution N(1s) spectra are reported and two distinct nitrogen species are shown to be present.

Estimates of the concentrations of the various species (nitrogen, sodium and titanium) present within the “probing depth” are reported.

Some general comments are made on the significance of these results to the surface modification of silica substrates used in h.p.l.c. and also on the limitations of the present approach.