Characterization and catalytic performance of potassium loaded on rice husk silica and zeolite nay for transesterification of jatropha seed oil

Rice husk silica (RHS) and NaY were used as supports for potassium (K) prepared from acetate buffer (B) and acetate (A) solutions. K loading did not destroy the NaY structure, but it caused a decrease in the surface area; the K species resided in micropores and on the external surface. In contrast, K loading resulted in the collapse and a decrease in the surface area of RHS. It was found that 12K/NaY-B was the most active catalyst for the transesterification of Jatropha seed oil. The minimum K content in K/NaY-B that provided complete conversion of the Jatropha seed oil was 11 wt%, and the biodiesel yield was 77.9%.

A reliable method of quantification of trace copper in beverages with and without alcohol by spectrophotometry after cloud point extraction

A new cloud point extraction (CPE) method was developed for the separation and preconcentration of copper (II) prior to spectrophotometric analysis. For this purpose, 1-(2,4-dimethylphenyl) azonapthalen-2-ol (Sudan II) was used as a chelating agent and the solution pH was adjusted to 10.0 with borate buffer. Polyethylene glycol tert-octylphenyl ether (Triton X-114) was used as an extracting agent in the presence of sodium dodecylsulphate (SDS). After phase separation, based on the cloud point of the mixture, the surfactant-rich phase was diluted with acetone, and the enriched analyte was spectrophotometrically determined at 537 nm. The variables affecting CPE efficiency were optimized. The calibration curve was linear within the range 0.285-20 µg L-1 with a detection limit of 0.085 µg L-1. The method was successfully applied to the quantification of copper in different beverage samples.

Produção de concentrados de ácidos graxos por hidrólise de óleos vegetais mediada por lipase vegetal

The aim of this work was to verify the ability of enzymatic crude extract from dormant castor bean seeds to yield concentrated fatty acids by hydrolysis of polyunsaturated vegetable oils such as corn and sunflower. The enzymatic extract exhibited higher activity towards corn oil, which was selected for further studies to determine optimum hydrolysis conditions by factorial design. Maximum hydrolysis percentage (≈84%) was reached at 60% wt. oil:buffer acetate 100 mM pH 4.5, 33 ºC and 5.0% wt. of crude extract after 70 min of reaction. These results suggest that the use of low-cost lipase from castor bean seeds has potential for oil hydrolysis.

Stability-indicating RP-HPLC method for simultaneous determination of gatifloxacin and flurbiprofen in binary combination

A stability-indicating RP-HPLC method is presented for determination of gatifloxacin and flurbiprofen in binary combination. Gatifloxacin, flurbiprofen and their degradation products were detected at 254 nm using a BDS Hypersil C8 (250 X 4.6 mm, 5 µm) column and mixture of 20 mM phosphate buffer (pH 3.0) and methanol 30:70 v/v as mobile phase. Response was linear over the range of 15-105 mg mL-1 for gatifloxacin (r² > 0.998) and of 1.5-10.5 mg mL-1 for flurbiprofen (r² > 0.999). The developed method efficiently separated the analytical peaks from degradation products (peak purity index > 0.9999). The method developed can be applied successfully for determination of gatifloxacin and flurbiprofen in human serum, urine, pharmaceutical formulations, and their stability studies.

A new approach to evaluate immobilization of β-galactosidase on Eupergit® C: structural, kinetic, and thermal characterization

This study aimed to evaluate β-galactosidase immobilization. For this purpose, the ionic strength of the buffer, reaction time, amount of the immobilization support, and pH were evaluated by a central composite design. Assay 8, which consisted of 1.5 mol L-1 phosphate buffer (pH 7.5) and a reaction time of 2 h, produced the maximum yield. Eupergit® C (400 mg) was subsequently used as an immobilization support. Immobilization kinetics wereinvestigated, and a significant increase in the yield was obtained after immobilization compared with that obtained from assay 8 (22.0 U mL-1 vs. 15.6 U mL-1). The enzyme efficiency of actuation was evaluated using o-nitrophenyl-β-D-galactopyranoside and lactose, with lactose providing better results. The reuse of β-galactosidase was evaluated, and more than 50% of the initial enzyme activity was maintained after five cycles of use. Enzyme characterization revealed that immobilization improved some aspects of the thermostability of β-galactosidase.

Preconcentration of copper from natural water samples using ligand-less in situ surfactant-based solid phase extraction prior to FAAS determination

In the present work, a simple and rapid ligand-less, in situ, surfactant-based solid phase extraction for the preconcentration of copper in water samples was developed. In this method, a cationic surfactant (n-dodecyltrimethylammonium bromide) was dissolved in an aqueous sample followed by the addition of an appropriate ion-pairing agent (ClO4-). Due to the interaction between the surfactant and ion-pairing agent, solid particles were formed and subsequently used for the adsorption of Cu(OH)2 and CuI. After centrifugation, the sediment was dissolved in 1.0 mL of 1 mol L-1 HNO3 in ethanol and aspirated directly into the flame atomic absorption spectrometer. In order to obtain the optimum conditions, several parameters affecting the performance of the LL-ISS-SPE, including the volumes of DTAB, KClO4, and KI, pH, and potentially interfering ions, were optimized. It was found that KI and phosphate buffer solution (pH = 9) could extract more than 95% of copper ions. The amount of copper ions in the water samples varied from 3.2 to 4.8 ng mL-1, with relative standard deviations of 98.5%-103%. The determination of copper in water samples was linear over a concentration range of 0.5-200.0 ng mL-1. The limit of detection (3Sb/m) was 0.1 ng mL-1 with an enrichment factor of 38.7. The accuracy of the developed method was verified by the determination of copper in two certified reference materials, producing satisfactory results.

DETERMINAÇÃO ESPECTROFOTOMÉTRICA DE METILDOPA EM ENSAIO DE DISSOLUÇÃO DE COMPRIMIDOS UTILIZANDO EXTRATO DE RABANETE COMO FONTE DE PEROXIDASE

An enzymatic spectrophotometric method for the determination of methyldopa in a dissolution test of tablets was developed using peroxidase from radish (Raphanus sativus). The enzyme was extracted from radish roots using a phosphate buffer of pH 6.5 and partially purified through centrifugation. The supernatant was used as a source of peroxidase. The methyldopachrome resulting from the oxidation of methyldopa catalyzed by peroxidase was monitored at 480 nm. The enzymatic activity was stable for a period of at least 25 days when the extract was stored at 4 or -20 ºC. The method was validated according to RDC 899 and ICH guidelines. The calibration graph was linear in the range 200-800 µg mL-1, with a correlation coefficient of 0.9992. The limits of detection and quantification in the dissolution medium were 36 and 120 µg mL-1, respectively. Recovery was greater than 98.9%. This method can be applied for the determination of methyldopa in dissolution tests of tablets without interference from the excipients.

USO DO PLANEJAMENTO EXPERIMENTAL PARA OTIMIZAÇÃO DE UM PROCEDIMENTO VOLTAMÉTRICO PARA DETERMINAÇÃO SIMULTÂNEA DAS CONCENTRAÇÕES DOS METAIS Zn, Cd, Pb E Cu LIVRES EM ÁGUA DE COCO

Optimization of the main parameters of SWASV using boron-doped diamond electrode was described for the simultaneous determination of Zn, Cd, Pb and Cu free in coconut water. The values of electroanalytical parameters studied were optimized with the factorial design and center composite design. The optimized parameters for the preconcentration of metals were -1.50 V for potential, and 240 s for deposition time. For SWV, the optimized value was 11.56 mV for step potential. In addition, frequency and pulse height were defined at 100 Hz and 55 mV, respectively. Furthermore, the concentration of the supporting electrolyte (acetate buffer, pH 4.7) was optimized in 0.206 mol L-1. The optimized procedure was applied in two samples of coconut water: natural and processed. The limits of detection (LOD) obtained for Zn, Cd, Pb and Cu were 7.2; 4.4; 3.3 and 1.5 µg L-1, respectively. The concentrations of Cd and Pb were not detected. On the other hand, the values found for the concentrations of Zn and Cu were: < LOD (29 µg L-1) and (6.8 ± 0.9) µg L-1 for the natural sample; and (85.8 ± 4.2) µg L-1 and (7.7 ± 0.6) µg L-1 for the processed sample, respectively.

PROPOSTA EXPERIMENTAL DIDÁTICA PARA O ENSINO DE ANÁLISE DE COMPONENTES PRINCIPAIS

Principal component analysis (PCA) is a chemometric method that allows for the extraction of chemical information that would otherwise be impossible to determine. Teaching chemometrics to undergraduates can contribute to the overall professional development and training of new teachers, whose profiles have been gaining attention due to the current demand for data interpretation. In this study, a didactic experiment involving PCA is proposed. Spectrophotometry was used in the ultraviolet-visible (UV-Vis) region to assess the behavior of anthocyanins extracted from red cabbage at different pH values. The results suggest the possible separation of anthocyanin structures into three distinct groups, according to their chemical characteristics displayed in acid, neutral, and basic media. The objective is to develop educational materials targeted to undergraduate courses, which encompass a larger number of concepts and introduce instrumental techniques currently being employed in both academic research and the industrial sector. Specifically, the proposed experiment introduces concepts related to spectrophotometry in the UV-Vis range and the PCA chemometric method. The materials used are easily accessible, and UV-Vis spectroscopy equipment is less expensive in comparison with other spectroscopy methods.

About the kinetics and mechanism of the reactions of 4-(2-pyridylazo)-resorcinol, with Zn2+, Cu2+ and Zn2++Cu2+ equimolar mixtures, in aqueous solutions

The kinetics and mechanism of the reactions between 4(2pyridylazo)-resorcinol and Zn2+, Cu2+ and Zn2++Cu2+ equimolar mixtures were studied. The reactions were performed in aqueous solution (pH = 8.5, borate buffer) and monitored spectrophotometrically at 500 nm using stopped-flow technique. Spectral and kinetic data indicate that the Zn2++Cu2+ equimolar mixture behaves as an unique species and it can be attributed to the interactions of Zn2+ and of Cu2+ with water molecules in the aqueous solution. A mechanism is proposed and the rate constants are calculated.

Use of experimental design in the optimisation of a solid phase preconcentration system for Cobalt determination by GFAAS

In this work is proposed a solid phase preconcentration system of Co2+ ions and its posterior determination by GFAAS in which fractional factorial design and response surface methodology (RSM) were used for optimization of the variables associated with preconcentration system performance. The method is based on cobalt extraction as a complex Co2+-PAN (1:2) in a mini-column of polyurethane foam (PUF) impregnated with 1-(2-pyridylazo)-naphthol (PAN) followed by elution with HCl solution and its determination by GFAAS. The chemical and flow variables studied were pH, buffer concentration, eluent concentration and preconcentration and elution flow rates. Results obtained from fractional factorial design 2(5-1) showed that only the variables pH, buffer concentration and interaction (pH X buffer concentration) based on analysis of variance (ANOVA) were statistically significant at 95% confidence level. Under optimised conditions, the method provided an enrichment factor of 11.6 fold with limit of detection and quantification of 38 and 130 ng L-1, respectively, and linear range varying from 0.13 to 10 µg L-1. The precision (n = 9) assessed by relative standard deviation (RSD) was respectively 5.18 and 2.87% for 0.3 and 3.0 µg L-1 cobalt concentrations.

Amperometric biosensor for ascorbic acid

A L-ascorbic acid biosensor based on ascorbate oxidase has been developed. The enzyme was extracted from the mesocarp of cucumber (Cucumis sativus) by using 0.05 mol L-1 phosphate buffer, pH 5.8 containing 0.5 mol L-1 NaCl. After the dialysis versus phosphate buffer 0.05 mol L-1 pH 5.8, the enzyme was immobilized onto nylon net through glutaraldehyde covalent bond. The membrane was coupled to an O2 electrode and the yielding reaction monitored by oxygen depletion at -600 mV using flow injection analysis optimized to 0.1 mol L-1 phosphate buffer pH 5.8, as the carrier solution and flow-rate of 0.5 mL min-1. The ascorbic acid calibration curve was linear from 1.2x10-4 to 1.0x10-3 mol L-1. The evaluation of biosensor lifetime leads to 500 injections. Commercial pharmaceutical samples were analyzed with the proposed method and the results were compared with those obtained by high-performance liquid chromatography (HPLC).

Interaction study of moxifloxacin with Cu(II) ion using square-wave voltammetry and its application in the determination in tablets

This work presents an electroanalytical method for the determination of moxifloxacin (MOXI) in tablets by its interaction with Cu(II) ion and subsequent electrochemical reduction at hanging mercury drop electrode (HMDE). A well-defined reduction peak at -0.21 V vs. Ag/AgCl in Phosphate buffer 0.04 mol L-1 pH 8.0 was observed for the complex reduction MOXI-Cu(II), using square-wave voltammetry (SWV). Using a 10 s of accumulation time at -0.40 V was found a limit detection of 3.60x10-8 mol l-1. The obtained results have shown good agreement with those obtained by spectrophotometric method.

Ascorbic acid determination using a carbon paste electrode modified with iron(III) ions adsorbed on humic acid

An amperometric sensor was constructed, by using humic acids to immobilize Fe3+ ions on a carbon paste electrode (CPE-HA-Fe), and used for ascorbic acid (H2A) determination. The cyclic voltammogram of the electrode showed electrochemical response due to the Fe3+/Fe2+ couple at E1/2=+0.78 V vs SCE, using 0.5 mol L-1 KCl and 0.2 mol L-1 acetate/0.020 mol L-1 phosphate buffer, at pH = 5.4, as supporting electrolyte. When H2A is added to the electrolyte solution it is observed an oxidation process. The oxidation current, obtained by chronoamperommetry at +0.87 V vs SCE, is proportional to the concentration, represented by the equation I(µA) = 7.6286 [H2A] (mmol L-1) + 1.9583, r = 0.9996, for concentrations between 0.0 and 1.4 mmol L-1. The electrode showed high stability and was used for H2A determination in a natural orange juice.

Methylene blue adsorption onto modified lignin from sugar cane bagasse

The adsorption kinetics and equilibrium of methylene blue (MB) onto reticulated formic lignin (RFL) from sugar cane bagasse was studied. The adsorption process is pH, temperature and ionic strength (µ) dependent and obeys the Langmuir model. Conditions for higher adsorption rate and capacity were determined. The faster adsorption (12 hours) and higher adsorption capacity (34.20 mg.g-1) were observed at pH = 5.8 (acetic acid-sodium acetate aqueous buffer), 50 ºC and 0.1 ionic strength. Under temperature (50 ºC) control and occasional mechanical stirring it took from 1 to 10 days to reach the equilibrium.