Biblioteca Digital

O presente trabalho teve como objetivo o desenvolvimento de procedimentos analíticos baseados na análise em fluxo com multicomutação, acoplada à detecção por fluorescência, espectrofotometria com longo caminho óptico ou quimiluminescência em guias de ondas (LCW), para a determinação de poluentes ambientais. Os procedimentos desenvolvidos atendem aos requisitos de sensibilidade e limite de detecção impostos pela legislação ambiental vigente e as características analíticas encontram-se em concordância com as tendências atuais de redução do consumo de amostras e reagentes, da geração de resíduos e de custo, apresentando alta freqüência de amostragem e operação simples. Os módulos de análises desenvolvidos são compactos, podendo ser adaptados para o monitoramento in situ. Com o acoplamento da cela LCW de 100 cm de caminho óptico a sistemas de análises por injeção em fluxo e monossegmentado, para medidas por turbidimetria e espectrofotometria, foi observada significativa melhora nos limites de detecção e sensibilidade. Discrepâncias entre o aumento de sensibilidade verificado e previsto pela lei de Beer têm relação com diferenças de dispersão em celas de 1 e 100 cm. Para a determinação espectrofotométrica de paraquat...

A potentiometric sensor constructed from a mixture of 25% (m/m) spinel-type manganese oxide (lambda-MnO2), 50% (m/m) graphite powder and 25% (m/m) mineral oil is used for the determination of lithium ions in a flow injection analysis system. Experimental parameters, such as pH of the carrier solution, flow rate, injection sample volume, and selectivity for Li+ against other alkali and alkaline-earth ions and the response time of this sensor were investigated. The sensor response to lithium ions was linear in the concentration range 8.6 x 10(-5) - 1.0 x 10(-2) mol L-1 with a slope 78.9 +/- 0.3 mV dec(-1) over a wide pH range 7 - 10 (Tris buffer), without interference of other alkali and alkaline-earth metals. For a flow rate of 5.0 mL min(-1) and a injection sample volume of 408.6 muL, the relative standard deviation for repeated injections of a 5.0 x 10(-4) mol L-1 lithium ions was 0.3%.

A calibration method was developed using flow injection analysis (FI) with a Gradient Calibration Method (GCM). The method allows the rapid determination of zinc In foods (approximately 30 min) after treatment with concentrated sulphuric acid and 30% hydrogen peroxide, and analysis with flame atomic absorption spectrometry (FAAS). The method provides analytical results with a relative standard deviation of about 2% and requires less time than by conventional FI calibration. The electronic selection of different segments along the gradient and monitoring of the technique covers wide concentration ranges while maintaining the inherent high precision of flow injection analysis. Concentrations, flow rates, and flow times of the reagents were optimized in order to obtain best accuracy and precision. Flow rates of 10 mL/min were selected for zinc. In addition, the system enables electronic dilution and calibration where a multipoint curve can be constructed using a single sample injection.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); A flow injection spectrophotometric procedure employing merging zones is proposed for direct bromopride determination in pharmaceutical formulations and biological fluids. The proposed method is based on the reaction between bromopride and p-dimethylaminocinnamaldehyde (p-DAC) in acid medium, in the presence of sodium dodecyl sulfate (SDS), resulting in formation of a violet product (lambda(max) = 565 nm). Experimental design methodologies were used to optimize the experimental conditions. The Beer-Lambert law was obeyed in a bromopride concentration range of 3.63 x 10(-7) to 2.90 x 10(-5) mol L-1, with a correlation coefficient (r) of 0.9999. The limits of detection and quantification were 1.07 x 10(-7) and 3.57 x 10(-7) mol L-1, respectively. The proposed method was successfully applied to the determination of bromopride in pharmaceuticals and human urine, and recoveries of the drug from these media were in the ranges 99.6-101.2% and 98.6-102.1%, respectively. This new flow injection procedure does not require any sample pretreatment steps. (C) 2014 Elsevier B.V. All rights reserved.

In this work, a novel flow-through solid-phase based chemiluminescence (CL) optical sensor is described for the trace determination of orthophosphate in waters exploiting the multisyringe flow injection analysis (MSFIA) concept with multicommutation. The proposed time-based injection flow system relies upon the in-line derivatisation of the analyte with ammonium molybdate in the presence of vanadate, and the transient immobilisation of the resulting heteropolyacid in a N-vinylpyrrolidone/divinylbenzene copolymer packed spiral shape flow-through cell located in front of the window of a photomultiplier tube. The simultaneous injection of well-defined slugs of luminol in alkaline medium and methanol solution towards the packed reactor is afterwards performed by proper switching of the solenoid valves. Then, the light emission from the luminol oxidation by the oxidant species retained onto the sorbent material is readily detected. At the same time, the generated molybdenum-blue compound is eluted by the minute amount of injected methanol, rendering the system prepared for a new measuring cycle. Therefore, the devised sensor enables the integration of the solid-phase CL reaction with elution and detection of the emitted light without the typical drawbacks of the molybdenum-blue based spectrophotometric procedures regarding the excess of molybdate anion...

A flow injection manifold is proposed for the sequential determination of titratable (total) acidity based on a pseudotitration and of tartaric acid based on the formation of a coloured vanadate complex. The method involves in-line dialysis prior to injection to avoid interference from the sample background absorption in the spectrophotometric detection. The changes in the colour of both reactions were monitored using two flow cells aligned in the optical path of a single spectrophotometer. Wine samples were analysed without any sample pre-treatment; table wines in the range 1–10 g l21 (total acidity) and 0.5–4 g l21 (tartaric acid) and port wines in the range 1–8 g l21 (total acidity) and 0.5–5 g l21 (tartaric acid). Sixteen samples can be measured per hour, and the results were comparable to those obtained by reference procedures for both determinations. RSDs (n = 10) generally lower than 3% were obtained

The enzymatic determination of L(-)malic and L(+)lactic acids in several types of wines by flow injection analysis (FIA) with spectrophotometric detection is described. This flow injection system, which incorporates a dialysis unit for adjusting the composition of the injected solutions to the requirements of the measuring system, enables determinations of these two organic acids without the need for any prior treatment of the wine samples, with a concentration interval of between 0.02 and 4 g/L, and a sampling rate of approximately 20 determinations per hour. The results obtained with this FIA method for various types of Portuguese wines are in good agreement with those of the batch method which uses the same enzymatic technique and are quite precise as they present a coefficient of variation below 2.5%.

Water treatment has become a source of concern as new pollutants and higher volumes of waste water must be treated. Emerging biological approaches, namely the use of bioreactors, for cleaning processes have been introduced. The use of bioreactors requires the development of efficient monitoring tools, preferably with realtime measurements. In this work, a couple of flow injection systems were developed and optimized for the potentiometric determination of fluoride to monitor a rotating biological contactor (RBC) bioreactor and a sequencing batch reactor (SBR) with offline and online sampling. Both the RBC and the SBR bioreactors were set up for the biodegradation of the halogenated organic compound 2fluorophenol and, as fluoride was a degradation byproduct, the process was monitored by following up its concentration. The described flow injection potentiometric methods enabled the fluoride determination within the required quantification range 0.10–100mM. The possible interferences from the growth medium were minimized inline. The determination rate was 78 h−1 for the offline monitoring of RBC and 50−1 h for the online monitoring of the SBR, with a sample consumption of 0.500mL and 0.133mL per determination, respectively. Furthermore...

A flow injection spectrophotometric procedure with on-line solid-phase reactor containing ion triiodide immobilized in an anion-exchange resin is proposed for the determination of adrenaline (epinephrine) in pharmaceutical products. Adrenaline is oxidized by triiodide ion immobilized in an anionic-exchange resin yielding adrenochrome which is transported by the carrier solution and detected at a wavelength of 488 nm. Adrenaline was determined in three pharmaceutical products in the 6.4 x 10-6 to 3.0 x 10-4 mol L-1 concentration range with a detection limit of 4.8 x 10-7 mol L-1. The recovery of this analyte in three samples ranged from 96.0 to 105 %. The analytical frequency was 80 determinations per hour and the RSDs were less than 1 % for adrenaline concentrations of 6.4 x 10-5 and 2.0 x 10-4 mol L-1 (n=10). A paired t-test showed that all results obtained for adrenaline in commercial formulations using the proposed flow injection procedure and a spectrophotometric batch procedure agree at the 95% confidence level.

A spectrophotometric flow injection method for the determination of paracetamol in pharmaceutical formulations is proposed. The procedure was based on the oxidation of paracetamol by sodium hypochloride and the determination of the excess of this oxidant using o-tolidine dichloride as chromogenic reagent at 430 nm. The analytical curve was linear in the paracetamol concentration range from 8.50 x 10-6 to 2.51 x 10-4 mol L-1 with a detection limit of 5.0 x 10-6 mol L-1. The relative standard deviation was smaller than 1.2% for 1.20 x 10-4 mol L-1 paracetamol solution (n = 10). The results obtained for paracetamol in pharmaceutical formulations using the proposed flow injection method and those obtained using a USP Pharmacopoeia method are in agreement at the 95% confidence level.

A systematic evaluation of a Fe2O3 graphite-epoxy tubular electrode was investigated through pH measurements in a single-channel flow injection system. The tubular electrode was obtained by deposition of a mixture of iron(III) oxide, graphite powder and epoxy resin into a hole previously made in the injection channel (of a polyuretane resin block). The effect of electrode composition and flow injection parameters (flow rate and injection sample volume) on the Fe2O3-tubular-electrode response was initially evaluated in quintuplicate (confidence level of 95%). The best potentiometric response (E/mV = 178.2 - 26.5 pH; r = 0.9995) was reached in the pH range 2 to 12 with an electrode composition in mass of 30% Fe2O3, 20% graphite and 50% epoxy resin, injection sample volume of 300 mL and a flow rate of 3.2 mL min-1. The frequency rate was 90 h-1 and a useful lifetime of at least six months (more than 2000 determinations) was obtained.

A simple, accurate and precise flow-injection turbidimetric procedure is reported for the determination of acetylcysteine in pharmaceutical formulations. The procedure is based on the precipitation of acetylcysteine with silver nitrate solution in acid medium and the insoluble salt produced was monitored at 410 nm. The analytical curve for acetylcysteine was linear in the concentration range from 1.0 × 10-4 to 1.0 × 10-3 mol L-1 with a detection limit of 5.0 × 10-5 mol L-1. The sampling rate was 60 h-1 and the relative standard deviations (RSDs) were less than 2.0% for 1.0 × 10-4 and 5.0 × 10-4 mol L-1 acetylcysteine solutions (n=10). The recovery of this analyte in four samples ranged from 97.6 to 103 %. A paired t-test showed that all results obtained for acetylcysteine in pharmaceutical products using the proposed flow-injection procedure and the official procedure agreed at the 95% confidence level.

A simple, accurate and precise flow-injection spectrophotometric procedure is reported for the determination of captopril in pharmaceutical formulations. In this procedure, captopril was oxidized by iron(III) and the iron(II) produced was spectrophotometrically monitored as iron(II)-1,10-phenantroline complex at 540 nm. The analytical curve for captopril was linear in the concentration range from 1.0 × 10-5 to 8.0 × 10-4 mol L-1 with a detection limit of 5.0 × 10-6 mol L-1. The recovery of this analyte in five samples ranged from 98.5 to 102.4%. The analytical frequency was sixty determinations per hour and the RSD was less than 0.2% for a captopril concentration of 4.0 × 10-4 mol L-1 (n = 10). A paired t-test showed that all results obtained for captopril in commercial formulations using the proposed flow injection procedure and a potentiometric procedure agreed at the 95% confidence level.

A spectrophotometric method for determination of fenoxaprop-p-ethyl herbicide using flow injection system has been proposed. The fenoxaprop-p-ethyl was converted into hydroxamic acid in the presence of hydroxylamine hydrochloride in alkaline media. The hydroxamic acid produced was further reacted with iron(III) to form red color tris iron hydroxamate complex. The absorbance of the complex was measured at 500 nm using flow injection system. The method shows a linear range between 1.0-20.0 µg mL-1 with molar absorptivity of 1.81 × 10(4) L mol-1 cm-1. The limit of detection and limit of quantification were calculated and found to be 0.29 ± 0.1 µg mL-1 and 0.96 ± 0.1 µg mL-1 respectively. Similarly the average limit of detection and limit of quantification were calculated for residue determination and were found 0.35 and 0.45 µg g-1 respectively for wheat grains and 1.2 and 1.5 µg g-1 respectively for barley grains. The sample through put was 90 samples h-1. The method was successfully applied to different grain samples.

Flow injection analysis (FIA) was applied to the determination of both chloride ion and mercury in water. Conventional FIA was employed for the chloride study. Investigations of the Fe3 +/Hg(SCN)2/CI-,450 nm spectrophotometric system for chloride determination led to the discovery of an absorbance in the 250-260 nm region when Hg(SCN)2 and CI- are combined in solution, in the absence of iron(III). Employing an in-house FIA system, absorbance observed at 254 nm exhibited a linear relation from essentially 0 - 2000 Jlg ml- 1 injected chloride. This linear range spanning three orders of magnitude is superior to the Fe3+/Hg(SCN)2/CI- system currently employed by laboratories worldwide. The detection limit obtainable with the proposed method was determin~d to be 0.16 Jlg ml- 1 and the relative standard deviation was determined to be 3.5 % over the concentration range of 0-200 Jig ml- 1. Other halogen ions were found to interfere with chloride determination at 254 nm whereas cations did not interfere. This system was successfully applied to the determination of chloride ion in laboratory water. Sequential injection (SI)-FIA was employed for mercury determination in water with the PSA Galahad mercury amalgamation, and Merlin mercury fluorescence detection systems. Initial mercury in air determinations involved injections of mercury saturated air directly into the Galahad whereas mercury in water determinations involved solution delivery via peristaltic pump to a gas/liquid separator...

Hydrothermal fluids near and above the critical point of water have unique and potentially very useful thermophysical properties. At present, the lack of knowledge of supercritical water chemistry hinders implementation of innovative hydrothermal technologies. The development of new experimental methods and application of molecular modeling tools is clearly warranted to provide a better understanding of the complex properties of aqueous systems at elevated temperatures and pressures. The thermodynamic, dielectric and transport properties of hydrothermal fluids are investigated using Molecular Dynamics (MD) simulation and flow injection techniques. The spatial hydration structures and self-diffusion coefficients of phenol, aniline and naphthalene in aqueous infinitely dilute solution are examined from ambient to supercritical conditions by means of MD simulations. It is shown that the solvation shell around aromatic molecules undergoes significant changes along the liquid-vapour coexistence curve and, essentially, disappears at supercritical conditions. The changes in hydration structures are reflected in the values of the self-diffusion coefficients which dramatically increase near the critical point of water. The thermodynamic and dielectric properties of the Simple Point Charge Extended (SPC/E) water model are examined over a broad range of sub- and supercritical states. Accurate thermodynamic and dielectric equations of state (EOS) for the SPC/E water model are presented. The parameterizations provide the most accurate...

A flow injection method for the quantitative analysis of ketoconazole in tablets, based on the reaction with iron (III) ions, is presented. Ketoconazole forms a red complex with iron ions in an acid medium, with maximum absorbance at 495 nm. The detection limit was estimated to be 1×10--4 mol L-1; the quantitation limit is about 3×10--4 mol L-1 and approximately 30 determinations can be performed in an hour. The results were compared with those obtained with a reference HPLC method. Statistical comparisons were done using the Student's t procedure and the F test. Complete agreement was found at the 0.95 significance level between the proposed flow injection and the HPLC procedures. The two methods present similar precision, i.e., for HPLC the mean relative standard deviation was ca. 1.2% and for FIA ca. 1.6%.

A flow injection method for the quantitative analysis of vancomycin hydrochloride, C66H75Cl2N9O24.HCl (HVCM), based on the reaction with copper (II) ions, is presented. HVCM forms a lilac-blue complex with copper ions at pH≅4.5 in aqueous solutions, with maximum absorption at 555 nm. The detection limit was estimated to be about 8.5×10-5 mol L-1; the quantitation limit is about 2.5×10-4 mol L-1 and about 30 determinations can be performed in an hour. The accuracy of the method was tested through recovery procedures in presence of four different excipients, in the proportion 1:1 w/w. The results were compared with those obtained with the batch spectrophotometric and with the HPLC methods. Statistical comparison was done using the Student's procedure. Complete agreement was found at a 0.95 significance level between the proposed flow injection and the batch spectrophotometric methods, which present similar precision (RSD: 2.1 % vs. 1.9%).

Artículo de publicación ISI; A continuous flow injection reaction-stopped flow detection method using derivative spectrophotometry was developed for the determination of cobalt and iron in mixtures. A conventional two-channel flow injection manifold was used to develop the analytical reactions between the analytes and ferrozine and drive the reaction products to the detector. After the signal (550 nm) reached the maximum the flow was stopped, the spectrum recorded between 400 and 700 nn and transformed into its first-derivative form using a Delta lambda of 1.6 nn. Cobalt andiron were thus determined in the range 1.1-25 mu g/ml and 0.15-6.0 mu g/ml, respectively. The detection limits were found to be 0.33 mu g/ml of cobalt and 0.045 mu g/ml of iron. The method was applied to the determination of the analytes in water samples.

Plackett-Burman and Quarter fraction 2(5-2) factorial designs were applied to evaluate a spectrophotometric flow injection method in order to determine phenol in water by using 4-aminoantipyrine (4-AAP) as derivatizing reagent. With a minimum number of experiments, the designs enabled the best conditions for phenol analysis: 80 cm and 180 cm reactors; flow-rates being: NH3 1.0 mL min-1; 4-AAP 0.35 mL min-1 and K3[Fe(CN)6] 0.35 mL min-1, [NH3] 0.064 mol L-1, [4-AAP] 9.84 × 10-3 mol L-1, [K3[Fe(CN)6]] 0.02 mol L-1, and an injection volume of 200 µL. With the optimized method it was possible to increase the lineal range from 0.3 µg mL-1 to 30 µg mL-1 and also to quantify the maximum allowable phenol concentration in water in comparison with other standard and flow injection methods whose lineal range are from 0.5 µg mL-1 to 20 µg mL-1 and from 0.5 µg mL-1 to 16 µg mL-1, respectively. The detection limit was of 0.13 µg mL-1 and the regression coefficient was of 0.9999, making possible a throughput of 36 determinations an hour with a minimum consume of reagent. With the proposed method, a distillation step was not necessary to remove sulfates but, when the sulfate:phenol ratio was higher than 83, the analytical signal for phenol increased 8%...