Débora Nobile Clausen

Improved selective cholesterol adsorption by molecularly imprinted poly(methacrylic acid)/silica (PMAA–SiO2) hybrid material synthesized with different molar ratios

The present paper describes the synthesis of molecularly imprinted polymer - poly(methacrylic acid)/silica and reports its performance feasibility with desired adsorption capacity and selectivity for cholesterol extraction. Two imprinted hybrid materials were synthesized at different methacrylic acid (MAA)/tetraethoxysilane (TEOS) molar ratios (6:1 and 1:5) and characterized by FT-IR, TGA, SEM and textural data. Cholesterol adsorption on hybrid materials took place preferably in apolar solvent medium, especially in chloroform. From the kinetic data, the equilibrium time was reached quickly, being 12 and 20 min for the polymers synthesized at MAA/TEOS molar ratio of 6:1 and 1:5, respectively. The pseudo-second-order model provided the best fit for cholesterol adsorption on polymers, confirming the chemical nature of the adsorption process, while the dual-site Langmuir-Freundlich equation presented the best fit to the experimental data, suggesting the existence of two kinds of adsorption sites on both polymers. The maximum adsorption capacities obtained for the polymers synthesized at MAA/TEOS molar ratios of 6:1 and 1:5 were found to be 214.8 and 166.4 mg g(-1), respectively. The results from isotherm data also indicated higher adsorption capacity for both imprinted polymers regarding to corresponding non-imprinted polymers. Nevertheless, taking into account the retention parameters and selectivity of cholesterol in the presence of structurally analogue compounds (5-α-cholestane and 7-dehydrocholesterol), it was observed that the polymer synthesized at the MAA/TEOS molar ratio of 6:1 was much more selective for cholesterol than the one prepared at the ratio of 1:5, thus suggesting that selective binding sites ascribed to the carboxyl group from MAA play a central role in the imprinting effect created on MIP.

OPTIMIZATION AND EFFECTS OF SOME ELECTRON ACCEPTORS ON THE PHOTOCATALYTIC DEGRADATION OF DIRECT RED 23 AZO DYE

ABSTRACT The photocatalytic degradation of aqueous solution of commercial azo textile dye, direct red 23 (DR23), was carried out in TiO 2 suspension at 30oC with the use of artificial and solar light sources. The photoreaction followed the first-order behavior with respect to the azo dye as a function of irradiation time. A 2 3 factorial design was carried out, in order to obtain the best experimental conditions, using the rate constant of DR23 degradation as the analytical response. Seven chemical species were determined from the normalized UV-Vis spectra during the DR23 degradation through Imbrie Q mode factor analysis followed by varimax and Imbrie oblique rotations. The addition of electron acceptors, such as H 2 O 2 , S 2 O 82- , and ClO 3- on the optimized conditions, was carried out to increase the DR23 degradation rate. Comparison of degradation efficiencies under artificial and solar radiation was examined in the presence of oxidants. Keywords : degradation; direct red 23; inorganic oxidant; photocatalysis; factorial design.

Efeitos dos parâmetros operacionais na fotodegradação do azo corante direct red 23 na interface dióxido de titânio/água

The decolorization and degradation of direct red 23 azo dye have been investigated in aqueous suspension of titanium dioxide under artificial irradiation. The effects of some operational parameters such as azo dye concentration, catalyst loading, and solution pH were investigated at 30.0 oC and optimized values were obtained. The first-order kinetic model was used to discuss the results. The UV-Vis spectra changes showed that the azo dye sample, collected after 6 h irradiation, was 98% decolorized while the residual total carbon was 97.9% degraded, indicating simultaneous photodecolorization and degradation.

Solid Phase Extraction to On-Line Preconcentrate Trace Cadmium Using Chemically Modified Nano-Carbon Black with 3-Mercaptopropyltrimethoxysilane

Carbon black (CB) grafted with 3-mercaptopropyltrimethoxysilane (3-MPTMS) was used as solid phase extractor for Cd2+ in a flow injection system coupled to flame atomic absorption spectrometry (FAAS). The influence of pH, buffer concentration, preconcentration flow rate and eluent concentration on preconcentration of Cd2+ were investigated by means of chemometric tools. The characterization of the adsorbent chemically modified was performed by Fourier transform infrared, scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, Raman spectroscopy and textural analysis. To perform the on-line preconcentration, 20.0 mL of a pH 7.0 Cd2+ solution at a flow rate of 4.0 mL min−1 was loaded through 30.0 mg of modified CB and then eluted with 1.0 mol L−1 HCl toward the FAAS instrument. The limits of detection and quantification were found to be 0.20 and 0.66 µg L−1, respectively. Addition and recovery tests carried out in real samples (mineral, tap and saline waters, and cigarette sample) and the analysis of certified reference material (TORT-2, lobster hepatopancreas reference) attested the applicability of proposed method.

Evaluation of a Multi-Walled Carbon Nanotube-Hemin Composite for the Voltammetric Determination of Hydrogen Peroxide in Dental Products

A simple, low cost sensor was developed for the voltammetric determination of hydrogen peroxide in mouthwash and dental whitening gel based on multi-walled carbon nanotubes incorporated with hemin. The sensor showed electrocatalytic activity toward the reduction of hydrogen peroxide in 0.05 mol L−1 Tris-HCl buffer solution (pH 7.0) using cyclic voltammetry. The optimum composition of paste was 20:10:70% (m/m/m) (multi-walled carbon nanotubes:hemin:mineral oil). A linear plot of the square root of scan rate vs. cathodic peak current showed that reduction of hydrogen peroxide is diffusion controlled. Using linear sweep voltammetry, the analytical curve ranged from 0.2 up to 1.4 mmol L−1 (r = 0.9996) with a sensitivity of 3.62 × 10−2 mA mol−1 L. The limits of detection and quantification were found to be 12.5 µmol L−1 and 41.7 µmol L−1, respectively. The developed method was applied for hydrogen peroxide determination in dental formulations. The results were compared with a volumetric method as a reference technique. No significant differences at the 95% level (paired student t test) were observed, thus demonstrating the accuracy of the sensor for the analysis of real samples.

Development of HPLC Method for Quantification of Orphenadrine, Paracetamol, and Caffeine in Pharmaceutical Formulations

A method for the determination of orphenadrine (ORPH), paracetamol (PAR) and caffeine (CAF) using HPLC was developed. The proposed method provides an easy sample preparation and low cost using a mobile phase consisting of 80% of water with direct determination of the active principles present in pharmaceutical formulations. The separation of ORPH, PAR and CAF was accomplished on a C18 colu at 5 ̊C at a flo ate of . L i -1 using acetonitrile/water (pH 2.5) as mobile phase (20:80, v/v). The method exhibits linear responses for ORPH, PAR and CAF in the concentration ranges of 0 – 150 mg L, 0 – 200 mg L and 0 – 200 mg L, respectively. The detection limits and quantification determined according to IUPAC recommendation were found to be 1.14 and 3.79 mg L -1 for ORPH, 0.05 and 0.17 mg L -1 for PAR and 0.02 and 0.07 mg L -1 for CAF. Recoveries varying from 98.02 up to 101.81% for two pharmaceutical formulations spiked with these analytes were achieved assuring the accuracy of the proposed method.