Célio Wisniewski

Evaluation of a simple and low cost potentiometric biosensor for pharmaceutical and in vivo adrenaline determination.

In this work the polyphenol oxidase (PPO) was the main component of a biosensor for adrenaline determination. The activity of this enzyme was measured in several vegetables. Banana (Musa sp.) extracts presented better results with 974 UA (units of activity). The biosensor was constructed with a polyethylene tube (0.8 mm i.d.) filled with: carbon paste containing 50 UA of the PPO in phosphate buffer (pH=7.00) solution and vaseline as agglutinant. When the biosensor was applied in medicine samples it provided a linear range from 8.00×10(-9) to 8.00×10(-4) mol L(-1); the results obtained with the proposed method and the Brazilian Pharmacopoeia method were in agreement (t-test). When it was applied in blood samples, the matrix-matching calibration was used, and the linear range was from 8.00×10(-7) to 8.00×10(-3) mol L(-1). In vivo studies were also done. The obtained results for those electrodes, which were inserted in the jugular vein of Wistar rats, were very promising.

On-Line Restricted Access Molecularly Imprinted Solid-Phase Extraction of Selective Serotonin Reuptake Inhibitors Directly from Untreated Human Plasma Samples Followed by HPLC-UV Analysis

In this article, we proposed a new restricted access molecularly imprinted polymer coated with bovine serum albumin (RAMIP-BSA) to be used in a multidimensional chromatographic system applied for the analysis of six selective serotonin reuptake inhibitors (SSRIs) directly from untreated human plasma samples. Fluoxetine, methacrylic acid and ethylene glycol dimethacrylate were used as the template, functional monomer and cross-linker, respectively. The imprinted polymer was covered with a bovine serum albumin (BSA) layer via the interconnections between the amine groups of the BSA using glutaraldehyde as a cross-linker. The obtained RAMIP-BSA was able to extract the SSRIs directly from the human plasma, while ∼100% of the proteins were excluded from the sample. Selectivity coefficients were calculated for fluoxetine (template) in comparison with venlafaxine, duloxetine, citalopram, fluvoxamine, paroxetine and sertraline, and the values were >1 in all cases, attesting to the presence of binding sites in the imprinted polymer. The method presented analytical ranges from 20 to 500 µg/L and correlation coefficients >0.99 for all of the SSRIs (fluoxetine, venlafaxine, duloxetine, citalopram, fluvoxamine and sertraline). Precision and accuracy presented variation coefficients and relative errors <14.5% and within the range of -19.18 to 3.8%, respectively. In all cases, the apparent recoveries were >85%. The proposed method was able to analyze three samples per hour, and each column was used at least 50 times without any significant changes in its performance.

Effect of Drawing on the Crystal–Amorphous Interphase, Remanent Polarization and Dielectric Properties of α-PVDF Films

The effect of drawing on the dielectric properties and on the remanent polarization of α-PVDF was investigated. Films were drawing at 150°C and a draw ratio of 4. Calorimetric analyses and X-ray diffraction results indicated that drawing increases the degree of crystallinity and reduces the crystal-amorphous interphase. As a consequence an increase in stable polarization and in the dielectric properties was observed, as well as a strong reduction in the metastable polarization. To explain these results it was suggested that the crystal-amorphous interphase might be responsible for both the metastable polarization and the αc relaxation of the polymer.

Ion Imprinted Polymer for Preconcentration and Determination of Ultra-Trace Cadmium, Employing Flow Injection Analysis with Thermo Spray Flame Furnace Atomic Absorption Spectrometry:

This work proposes a preconcentration method using an ion imprinted polymer (IIP) for determination of cadmium, in several samples, employing a mini-column filled with the polymer coupled into a flow injection analysis system with detection by thermospray flame furnace atomic absorption spectrometry (FIA-TS-FF-AAS). The polymer was synthesized via bulk using methacrylic acid and vinylimidazole as a functional monomer. For the FIA system initial assessment, the variables: pH, eluent concentration and buffer concentration were studied, employing a 23 full factorial design. To obtain the optimum values for each significant variable, a Doehlert matrix was employed. After the optimization conditions as: pH 5.8, eluent (HNO3) concentration of 0.48 mol L−1 and buffer concentration of 0.01 mol L−1, were adopted. The proposed method showed a linear response in the range of 0.081–10.0 μg L−1, limits detection and quantification of 0.024 and 0.081 μg L−1, respectively; preconcentration factor of 165, consumptive index of 0.06 mL, concentration efficiency 132 min−1, and frequency of readings equal to 26 readings h−1. The accuracy was checked by analysis of certified reference materials for trace metals and recovery tests. The obtained results were in agreement with 95% confidence level (t-test). The method was adequate to apply in samples of: jewelry (earrings) (2.38 ± 0.28 μg kg−1), black tea (1.09 ± 0.15 μg kg−1), green tea (3.85 ± 0.13 μg kg−1), cigarette tobacco (38.27 ± 0.22 μg kg−1), and hair (0.35 ± 0.02 μg kg−1).

A Homemade Autosampler/Injector Commutator for Flow Injection Analysis

An autosampler/injector commutator for flow injection analysis (FIA) was constructed with electronic components of used equipments. The apparatus is controlled by commercially available multifunctional interface (PCL711B) connected to a personal computer, and the software was written in Visual Basic language. The system was applied to water analysis and it presented satisfactory results. The low cost and simplicity are the principal characteristics of the autosampler/injector commutator.

Assessment of cadmium and iron adsorption in sediment, employing a flow injection analysis system with on line filtration and detection by flame atomic absorption spectrometry and thermospray flame furnace atomic absorption spectrometry.

This work presents an evaluation of iron and cadmium adsorption in sediment of the Furnas Hydroelectric Plant Reservatory located in Alfenas, Minas Gerais (Brazil). The metal determination was done employing a flow injection analysis (FIA) with an on-line filtering system. As detection techniques, flame atomic absorption spectrometry (FAAS) for iron and thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) for cadmium determinations were used. The developed methodology presented good limits of detection, being 190 μg L(-1) for iron and 1.36 μg L(-1) for cadmium, and high sampling frequency for both metals 144 and 60 readings h(-1) for iron and cadmium, respectively. Both metals obey the Langmuir model, with maximum adsorptive capacity of 0⋅169 mg g(-1) for iron and 7⋅991 mg g(-1) for cadmium. For iron, a pseudo-first-order kinetic model was obtained with a theoretical Q(e)=9⋅8355 mg g(-1) (experimental Q(e)=9⋅5432 mg g(-1)), while for cadmium, a pseudo-second-order kinetic model was obtained, with a theoretical Q(e)=0.3123 mg g(-1) (experimental Q(e)=0⋅3052 mg g(-1)).

Molecularly imprinted probe for solid‐phase extraction of hippuric and 4‐methylhippuric acids directly from human urine samples followed by MEKC analysis

Hippuric acid (HA) and 4‐methylhippuric acid (4‐MHA) are metabolites as well as biological indicators for toluene and xylenes, respectively, and their determination in urine samples is very important, in order to monitor the occupational exposition to these solvents, ensuring a safe working environment. Thus, this paper describes the synthesis and characterization of a probe impregnated with molecularly imprinted polymers (MIPs) for the solid‐phase extraction of HA and 4‐MHA directly from untreated urine samples followed by micellar electrokinetic chromatography (MEKC) analyses. The MIP probe selectivity was compared to the non‐imprinted polymer probe. The MEKC separations were carried out in 50 mmol/L sodium tetraborate pH 10.0/0.5 mmol/L cetyltrimethylammonium bromide aqueous solution, with a constant voltage of –15 kV. The system variables were optimized to provide ideal conditions for the extraction and desorption of the analytes, as well as for the MEKC analyses. The method was linear from 0.5 to 5.0 g/L for both analytes, with correlation coefficients > 0.994. Precisions and accuracies, expressed as relative standard deviation and relative error, were < 20.0 and within –15.4 to 16.6%, respectively, in accordance with the United States Food and Drug Administration recommendation. The MIP probe has proven to be simple, cheap, resistant, and synthetically reproducible, being successfully used to analyze both HA and 4‐MHA from real samples.

Digital Image Analysis for the Colorimetric Determination of Aluminum, Total Iron, Nitrite and Soluble Phosphorus in Waters

ABSTRACT A webcam was used to determine Al(III), total Fe, , and in waters by digital image colorimetry. Least squares regression was used to obtain a quadratic equation based on the red, green, blue, hue, saturation, and brightness color values, which allowed the evaluation of the wavelength of maximum absorption of the analytes. To determine the concentrations, the red, green, and blue intensities were converted into absorbances. For Al(III) and determination, the best results were attained when the absorbances relative to the green color were used. For total Fe and determination, the combined absorbances of green and blue and red and blue color led to higher sensitivity (slope) and coefficients of determination. The limits of detection for Al(III), total Fe, , and determinations were 2.59 × 10−7, 3.58 × 10−7, 1.09 × 10−7, and 1.65 × 10−7 mol L−1, respectively. The values for total Fe, , and were lower than comparative spectrophotometric techniques. The limits of detection were compatible with the Brazilian legislation for potable water. The developed procedure was successfully used for the determination of the wavelength of maximum absorption and the concentration of the analytes in water and wastewater. The reported procedure is simple, versatile, and low cost and demonstrates that a webcam is a suitable detector for determining Al(III), total Fe, , and in water with adequate accuracy and precision.

Determination of Uranium in Environmental Water by Flow Injection Analysis using a Hybrid-Imprinted Polymer

A hybrid imprinted polymer was synthesized using 3-(trimethoxysilyl) propylmethacrylate 4 vinylpyridine as the inorganic monomer, metacrilic acid as the organic monomer, and the uranile ion as the template. The synthesis was performed via a sol-gel technique. The polymer was sieved and introduced into a minicolumn, which was coupled in a flow injection system with spectrophotometric detection to preconcentrate uranium and allow its determination at low concentration. The method had a linear dynamic range between 2.0–100 µg L−1, a detection limit of 0.40 µg L−1, a preconcentration factor of 97, a concentration efficiency of 19.4 min−1, a consumptive index of 0.227 mL, and a sampling frequency of 10 analyzes h−1. The imprinted polymer had an adsorptive capacity of 1.77 mg g−1. The method was employed for the determination of uranium in effluent and river water. The precision, expressed as the relative standard deviation, was lower than 5.5%. The accuracy was investigated by comparison with alpha spectrometry; the results were statistically the same. The speed of the process is an advantage compared to the traditional alpha spectrometry. In addition, the present method is green because of the low consumption of sample and reagents and is a useful alternative for uranium determination.

A spectrophotometric flow injection system for streptomycin determination in veterinary samples.

In this work a spectrophotometric flow injection analysis system for streptomycin determination in veterinary samples, is being proposed. The method is based on streptomycin alkaline hydrolysis that forms guanidine, followed by the reaction with Fe(II). The colored product has absorption peak at 520 nm. To evaluate and optimize the system parameters, chemometrics tools, such as factorial design, Pareto chart and Doelhert design, were used. The veterinary samples are diluted in water and introduced in the FIA system, therefore no sample preparation is required. The optimized system presented: linear range of 60 up to 1000 mg L(-1), limit of detection of 18 mg L(-1) and sampling rate of 36 readings per hour. The precision was checked and the CV for veterinary sample readings were always less than 6.5%. The accuracy was studied by comparison with chromatographic method, thus, five samples of pharmaceutical veterinary were determined by HPLC and by the proposed method, and the results are in agreement (t-test, p=0.05).