Endcapping of Octadecyl Bonded Silica by Atomic Layer Deposition for Separation of Basic Compounds

In this article, a novel method for preparation of octadecyl-bonded silica (ODS), which is highly inert to basic compounds, is described. This method is based on end-capping reaction of hexamethyldisilazane with residual silanol groups on ODS packing using atomic layer deposition (ALD) technique. Chromatographic performance in terms of retention factor and tailing factor of the resulting phases is evaluated using phenol/pyridine and naphthalene/amitriptyline pairs as probes. The results are compared with those for the same packing treated by liquid phase method and for the commercial products including Zorbax SB-C18 and Kromasil C18. The separation characteristics of the end-capped ODS phase obtained by ALD appear to be better compared with that of liquid phase method and comparable with or even better than the commercial products studied. Being solvent-free process amenable to mass production, the ALD method provides an economical and environmentally benign approach to manufacture packing materials for high-performance liquid chromatography.