Caracterizações fisicas, quimicas e cromatograficas de silicas modificadas por camadas de oxidos metalicos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

The aim of this work was to characterize physically, chemically and chromatographically HPLC stationary phases prepared with silica modified with zirconium titanium and aluminum oxides and having polymethyloctylsilane, PMOS, immobilized onto the surfaces. The physical tests used were X Ray Fluorescence (XRF), X Ray Absorption (XAS), X Ray Diffraction (XRD), Infrared (IR) Spectroscopies and Scanning Electronic Microscopy (SEM). These tests are important to determine the content of metallinked to the silica by the metallization process, to suggest a structure for the metallic oxide layers, to verify if this layer is bonded or only deposited onto the silica, to verify changes in the structure of the silica and to see if the ocorrence of cristallinity. The physical tests showed that zirconization process gave the highest metal concentration on silica and allowed the suggestion of a structure for the zirconized and titanized silicas. This was not possible for the aluminized silica. The used chemical tests were elemental analysis (C,H,N) and tests of metallized silica resistences in acidic and basic media. The former measured the percent carbon after metallization, after PMOS immobilization, after extraction of the polymer excess with an appropriate solvent and after use as HPLC (High Performance Liquid Chromatography) stationary phases. The resistence tests showed that titanium protects silica better than zirconium. The chromatographic tests were carried out in both normal phase and reverse phase conditions, the former using the modified silicas directly and the latter after deposition of PMOS. These tests evaluated the chromatographic parameters of efficiency (N), asymmetry (As) and retention factor (k) to determine which stationary phases gave the best performance. It was verified that titanized silica had the best chromatographic performance in both normal phase (~40100 plates/m) and reversed phase (~69600 plates/m). The zirconized and aluminized silica had poorer efficiencies and longer retention times.

ASSUNTO(S)

silica metalização

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