Analytica Chimica Acta 550 (2005) 137–143 Characterization of zirconized silica supports for HPLC Anizio M. Faria, Daniel R. Magalh˜ aes, Kenneth E. Collins, Carol H. Collins ∗ Instituto de Qu´ ımica, Universidade Estadual de Campinas, P.O. Box 6154, 13084-971 Campinas, SP, Brazil Received 9 March 2005; received in revised form 23 June 2005; accepted 25 June 2005 Available online 1 August 2005 Abstract The preparation and characterization of zirconized silica has been investigated. The material was prepared via the reaction of silica with zirconium tetrabutoxide, optimized by a central composite design and response surface methodology. The new material was characterized by nitrogen adsorption-desorption investigations (BET/BJH) showing specific surface areas adequate for use as a chromatographic support. DRUVS, FTIR, XPS, XAS, XRF and SEM methods also were used to characterize the new material. It was shown that silica networks were not significantly modified with the introduction of zirconium. Surface analyses show that there is appreciable element enrichment at the surface, while significant changes in binding energies of Zr 3d, Si 2p, and O 1s have been detected. The above observations indicate that Si O Zr bonds were formed, with zirconium grafted onto the silica surface, yielding a support suitable for HPLC. © 2005 Elsevier B.V. All rights reserved. Keywords: Chromatographic support; Zirconized silica; XAS; XPS 1. Introduction In spite of its widespread use in RP-HPLC, silica-based chromatographic phases tend to be limited in various aspects. Many of these limitations are related to the high activity of silanol groups that remain unreacted after the process of coat- ing or bonding the liquid phase onto a silica support. Residual silanols interact with alkaline mobile phases, causing silica hydrolysis and, consequently, loss of stationary phase [1,2]. Also, unreacted silanols can adsorb basic compounds, induc- ing peak tailing and loss of chromatographic resolution [3]. The current literature concerning chromatographic packings for RP-HPLC relates several approaches in order to mini- mize these undesirable silanophilic effects. Most of them are based on the protection of silanols by reacting them with silanizing agents, which either hinder residual silanols or avoid their activity [4–10]. However, one vulnerable point, the siloxane linkages, can still be exposed due to incomplete or non-uniform coverage of the surface and undergo attack in either acidic (pH < 2) or basic (pH > 9) media. ∗ Corresponding author. Tel.: +55 19 3788 3059; fax: +55 19 3788 3023. E-mail address: chc@iqm.unicamp.br (C.H. Collins). As alternatives to silica both organic polymers and other metal oxides have been suggested. The former is inert and stable chemically throughout the pH range from 1 to 13 but presents, as disadvantages, lower efficiencies, less repro- ducibility and significantly lower mechanical rigidity [11]. Zirconia, titania and alumina have all been suggested as sub- stitutes for silica. These oxides have much greater stabilities over wider pH ranges. However, the problems with acidic hydroxyls remain, derivatization reactions are problematic and these materials do not possess the range of particle and pore size available with silica [11–14]. Several recent papers from our laboratory have shown the good performance of stationary phases supported on silica modified by zirconium [15–19] or titanium [20–22] oxides. Silica and zirconia/titania can be physically mixed or chem- ically bonded, with covalent Si O M bonds. As already mentioned, native zirconia [23–25] or titania [26,27] are much more resistant to hydrolysis than silica over a wide pH range. Therefore, silica modification with these two oxides, besides modifying the silanol groups, may also incorporate some of the chemical stability of zirconia and titania into the chromatographic support. Also, the higher the percent of modifying metal, the higher should be the silanol cover- 0003-2670/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2005.06.066