Evaluation of the Hybrid Membrane of ZnO Particles Supported in Cellulose Acetate for the Removal of Lead.

Water polluted by discarded heavy metals such as lead is creating a global pollution problem. In this work, adsorption of Pb(II) was realized in batch studies by a hybrid membrane of cellulose acetate with ZnO particles. First, ZnO particles were prepared by precipitation and immobilized on the membrane. The hybrid membrane was elaborated by interfacial polymerization. The structure and surface were characterized based on Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Batch experiments were carried out under different conditions where the number of particles of ZnO present in the membrane and the pH of the aqueous solution were varied. The Langmuir and Freundlich isotherm models were evaluated in the best adsorption conditions. Data fitted well with a Langmuir model with a maximum adsorption capacity of 15.55 mg·g-1, which was similar for this type of materials. Thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy showed that the process was spontaneous and favorable. The hybrid membrane was evaluated in simulated wastewater of the battery industry with a superior efficiency of up to 97%; without the medium, it did not generate interference. These results suggest that Pb(II) removal by hybrid membrane is possible.

Size exclusion chromatography (SEC-HPLC) as an alternative to study thrombin inhibition.

In vitro analysis of anticoagulant compounds with a potential use as antithrombotic drugs, has been traditionally performed using techniques like spectrophotometry, turbidimetry, as well as electrochemical and clinical assays. Although, these techniques have some disadvantages such as: the inability to measure the total biological activity of thrombin, interferences and, sometimes, the quantitative determination of the inhibition ratio is not accurate. In the present work, the conversion of fibrinogen to fibrin was monitored by molecular exclusion chromatography (SEC-HPLC) in three different reaction systems. An inhibition percentage of 43.19±2.02% was obtained using heparin as an anticoagulant, in addition to the determination of the percentage of heparin bonded to thrombin. This methodology has not been previously described and has high potential for the determination of anticoagulant capacity with higher precision, the determination of thrombin's total biological activity and the quantitative determination of the inhibition ratio.

Application of an activated carbon-based support for magnetic solid phase extraction followed by spectrophotometric determination of tartrazine in commercial beverages.

A method is presented for magnetic solid phase extraction of tartrazine from nonalcoholic beverages. The method involves the extraction and clean-up by activated carbon covered with magnetite dispersed in the sample, followed by the magnetic isolation and desorption of the analyte by basified methanol. The tartrazine eluted from the magnetic support was determined by spectrophotometry. Under optimal conditions, the linear range of the calibration curve ranges from 3 to 30 mg L(-1), with a limit of detection of 1 mg L(-1). The method was validated by comparing the results with those obtained by HPLC. A precision of <5.0% was obtained in all cases and no significant differences were observed (P < 0.05).

Determination of quinolones in milk samples using a combination of magnetic solid-phase extraction and capillary electrophoresis.

A magnetic solid-phase extraction (MSPE) method combined with capillary electrophoresis for the simultaneous determination of seven quinolones (QNs) (danofloxacin, ciprofloxacin, marbofloxacin, enrofloxacin, difloxacin, oxolinic acid, and flumequine), using (S)-(+)-6-methoxy-α-methyl-2-naphthaleneacetic acid as internal standard, in milk samples was developed. The variables involved in the preconcentration magnetic procedure were: the composition of the magnetic support composition, the sample pH, and the weight of magnetic adsorbent used. The variables were optimized using a simplex-lattice design. Different magnetite covered with octyl-phenyl silica adsorbents were synthesized by varying the molar ratio of phenyltrimethylsilane and octyltrimethoxysilane; the solids were evaluated for QN preconcentration. Under optimal conditions, a linear range was obtained from 27 to 1000 µg L(-1) with limits of detection ranging from 9 to 12 µg L(-1) for the seven QNs. The absolute recoveries of the seven QNs at three different spiked levels (40, 150, and 400 µg L(-1) ) ranged from 74% to 98% with a relative standard deviation less than 10% in all cases. The proposed method was applied to analyze 20 whole milk samples of different brands. All samples were positive for the presence of QN residues; in some cases, extract dilution was required. The concentrations found are in the range from 31.1 to 5047.3 µg L(-1) . Marbofloxacin was the most frequently found. The method proposed offers advantages in terms of simplicity, sensitivity, efficiency, cost, and analysis time making it an alternative for the analysis of QNs in whole milk samples.

Determination of oxytetracycline in milk samples by polymer inclusion membrane separation coupled to high performance liquid chromatography.

The determination of oxytetracycline in milk samples using a polymer inclusion membrane concept with high performance liquid chromatography (HPLC) was studied. The membranes developed are composed by cellulose acetate as polymer base, Cyanex 923 as carrier and o-nitrophenyl octyl ether as plasticizer. In the optimal conditions, the method exhibits good linearity in the range 0.03-0.20 mg L(-1) with a limit of detection and quantification of 8.2 and 27.3 µg L(-1) respectively. The method was successfully applied to the analysis of milk samples with high selectivity.