Desenvolvimento de uma nova fase estacionária com o método da complexação metal-quitosana para colunas de CLC e HPLC

Abstract

Silica is considered the main chromatographic support used in stationary phases (SP), but the instability presented by silica at extreme pH is the main limitation related to its use, which may cause hydrolysis or solubilization of the silica. The solution to this problem has been the coating of the silica with other metal oxides. This work suggests a silica modification method using a mixture of lithium, barium, zirconium, aluminum, titanium oxides through the chitosan metal complexation method, with the goal to be applied as a SP in classical liquid chromatography (CLC) and high performance liquid chromatography (HPLC). A material was developed, called Exp 1, in oxide ratio of 65% SiO2, 29% Li2O, 1% ZrO2 and 5% BaO. The calcination step in this material synthesis was optimized, varying parameters such as temperature, heating rate and length time, what it was observed the best properties in 350 °C, 3 °C/min and 3 hours, respectively. The optimized material was characterized by N2 adsorption/desorption technique by BET’s method, presenting a surface area of 220 m2/g. Another SP, called Exp M, was developed with silica and varying the oxides used in relation to the previous one, there was used a mixture of lithium, titanium, barium and alumina oxides incorporated into the silica (19% Li2O, 1% TiO2, 5% BaO, 35% Al2O3 and 40% SiO2). This material had a surface area of 249 m2/g and it was applied for CLC analysis, with a particle size of 45-100 μm, for separation of monoacylglycerides (MAG), diacylglycerides (DAG) and triacylglycerides (TAG) which separation was not observed as expected. However, the same analysis was performed using commercial silica as stationary phase, and the observed results were not satisfactory, it showed the need for optimization of the separation method. Different analytical standards were used to test the efficiency of the developed SP, Exp 1 and Exp M, on HPLC. The first material tested was Exp 1, in the first test using polar compounds derived from benzyl alcohol oxidation (benzophenone, benzoic acid, benzyl alcohol and benzaldehyde) it was observed that there was coelution of three of the four compounds analyzed. In the analysis of the less polar compounds (naphthalene, benzene, nitrophenol and toluene) the four analytes were coeluted, so the SP was not efficient. Using as SP the Exp M, they were made with the less polar analytes, where there was coelution of the analytes, since the coelution of the less polar compounds, polar compounds from the benzyl alcohol oxidation were used and it was observed that happened the separation of the most polar compounds to the less polar. The efficiency of SP, Exp M, was also tested in the separation of some polar acid compounds (mercaptobenzoic acid, cyanobenzoic acid and dimethylaminobenzoic acid), where the compounds were separated. The developed SP were characterized before and after use of the column by the thermogravimetric analysis (TGA), X-ray diffraction (DRX), and Fourrier Transform infrared spectroscopy (FTIR) instrumental techniques, to evaluate its stability, where the materials were not totally stable.