A multi-commuted flow system was developed to determine propylthiouracil (PTU) based on the reaction of its thiol form with iminoquinone radical generated by the oxidation of N,N-dimethyl-p-phenylenediamine in an alkaline medium. PTU can be found in tautomeric forms and the tautomeric equilibrium was displaced to enhance the thiol form. However, the reaction product is unstable and its residence time in the flow path was carefully investigated. The proposed procedure showed good precision (< 1.5%) and a limit of detection (3s) of 0.11 mg L-1. High recoveries were obtained in the validation test. The procedure was employed for propylthiouracil determination in medications.

Desenvolveu-se um procedimento para determinação de cobre, ferro, chumbo e zinco em amostras de gasolina. O procedimento foi baseado na pré-concentração dos metais empregando uma resina modificada com o ácido 3,4-dihidroxibenzóico (XAD-DHB), seguida da dessorção com solução ácida. Os analitos no eluato foram determinados por espectrometria de absorção atômica em chama multielementar seqüencial (FS-FAAS). As amostras de gasolina foram preparadas como microemulsões misturando-se 80 mL de amostra com 17 mL de propan-1-ol e 3 mL de solução tampão (pH 10). As variáveis físico-químicas que influenciam no processo de extração foram otimizadas. Os LODs obtidos foram 2,2 µg L-1 para Fe, 3,1 µg L-1 para Cu, 2,3 µg L-1 para Pb, e 2,6 µg L-1 para Zn. Os valores de RSDs das concentrações dos analitos nas amostras enriquecidas com 0,05 e 0,1 mg L-1 de cada metal variaram de 5,8 a 9,7%. As recuperações variaram de 82 a 99%. O método foi aplicado na determinação dos analitos em níveis de µg L-1 em amostras de gasolinas coletadas em postos revendedores de Salvador, BA, Brasil.

A procedure was developed for determination of copper, iron, lead and zinc in gasoline. The procedure was based on the preconcentration of metals using a resin modified with 3,4-dihydroxybenzoic acid (XAD-DHB), followed by desorption with an acid eluent. The components in the eluate were then determined by fast sequence flame atomic absorption spectrometry (FS-FAAS). The gasoline samples were prepared as microemulsions by mixing 80 mL of sample with 17 mL of propan-1-ol and 3 mL of a buffer solution (pH 10). The chemical and physical variables influencing the extraction were optimized. The LODs obtained were 2.2 µg L-1 Fe, 3.1 µg L-1 Cu, 2.3 µg L-1 Pb and 2.6 µg L-1 Zn. The RSDs ranged from 5.8 to 9.7% in samples spiked with 0.05 and 0.1 mg L-1 of each metal and recoveries varied from 82 to 99%. The procedure was suitable for determination of the analytes at µg L-1 levels in gasoline samples collected from several gas stations in Salvador, State of Bahia, Brazil.

Neste trabalho foi avaliada a eficiência de dois procedimentos para digestão ácida de amostras de biodiesel visando à determinação de Ca, P, Mg, K e Na por espectrometria de emissão óptica com plasma acoplado indutivamente com configuração axial (ICP OES). Nas digestões em sistema aberto, foi utilizada a mistura contendo ácidos nítrico, sulfúrico e peróxido de hidrogênio e aquecimento condutivo; enquanto que no procedimento empregando forno de microondas com cavidade foi utilizada a mistura contendo ácido nítrico e peróxido de hidrogênio. Os procedimentos foram avaliados considerando-se limites de quantificação, precisão, acidez final dos digeridos e teor de carbono residual. Os teores de carbono residual nos digeridos foram 0,358 ± 0,012% para o sistema aberto com aquecimento convencional e 0,614 ± 0,023% para o sistema fechado com aquecimento assistido por radiação microondas, o que demonstra a alta eficiência dos procedimentos propostos. O sistema de digestão em forno de microondas com cavidade resultou em maior rapidez, segurança e resultados analíticos com percentuais de recuperação de 89,0-103,0% e desvios menores que 5%. Os limites de detecção obtidos, < 0.40 µg g-1, são adequados para a determinação dos analitos, conforme os limites estabelecidos na legislação brasileira. Três amostras de biodiesel produzidas de diferentes fontes foram analisadas. Em comparação com outros procedimentos propostos na literatura, o procedimento desenvolvido usando forno de microondas com cavidade apresenta vantagens, tais como não necessitar de soluções orgânicas para calibração e não usar solventes orgânicos tóxicos.

In the present work, the efficiency of two procedures for the digestion of biodiesel was investigated for the simultaneous determination of Ca, P, Mg, K and Na by axial view ICP OES. In the open system with conventional heating, concentrated nitric and sulfuric acids were added to the samples, and the addition of hydrogen peroxide completed the digestion. In the microwave-assisted closed system, complete digestion was performed using concentrated nitric acid and hydrogen peroxide. The analytical performances were evaluated through limits of quantification, precision of the overall procedures, final acidity of the digests, and residual carbon contents. The contents of residual carbon for the biodiesel samples digested were 0.358 ± 0.012% using the open system with conventional heating and 0.614 ± 0.023% using the microwave-assisted closed vessel system, demonstrating the high efficiency of both proposed procedures. The optimized microwave-assisted decomposition procedure produced the fastest, safest and most accurate analytical results with recoveries of 89.0-103.0% and deviations lower than 5% in most cases. Low limits of detection were obtained (< 0.40 µg g-1), adequate for the established limits set out in Brazilian legislation for these analytes. Three biodiesel samples produced from different oil sources were analyzed. In comparison with other procedures proposed in the literature, the developed procedure using the microwave-assisted closed system is advantageous because it neither require organic standard solutions for calibrations nor use toxic organic solvents.

Um procedimento espectrofotométrico de análise em fluxo foi desenvolvido para determinação de Captopril (CPT) e N-acetil-L-cisteína (NAC) em formulações farmacêuticas baseado na reação com radical iminoquinona produzido pela oxidação de N,N-dimetil-p-fenilenodiamina (DMPD) em meio ácido. A ordem de adição de reagentes foi avaliada e os parâmetros analíticos foram otimizados. As faixas lineares de concentração foram de 2,5-90 e de 5,0-50 mg L-1 para CPT e NAC, respectivamente. Os limites de detecção (3σ) foram calculados em 0,22 e 1,8 mg L-1 e desvios padrão relativos (N = 10) foram inferiores que 1,0 e 2,1% para CPT e NAC, respectivamente. O procedimento foi empregado para a determinação de CPT e NAC em diversas formulações farmacêuticas e os resultados concordaram com os obtidos pelos métodos de referência para 95% de confiabilidade aplicando teste-t pareado.

A spectrophotometric flow analysis procedure to determine Captopril (CPT) and N-acetyl-L-cysteine (NAC) in pharmaceutical formulations was developed based on the reaction with iminoquinone radical produced from the N,N-dimethyl-p-phenilenediamene (DMPD) oxidation in acid medium. The reagents addition order was evaluated and analytical parameters were optimized. The linear concentrations ranges were 2.5-90 and 5.0-50 mg L-1 for CPT and NAC, respectively. Limits of detection (3σ) were calculated at 0.22 and 1.8 mg L-1 and the relative standard deviation (N = 10) were lower than 1.0 and 2.1% for CPT and NAC, respectively. The procedure was employed for CPT and NAC determination in diverse pharmaceutical formulations and by applying paired t-test the results were in agreement with those obtained by reference methods for 95% confidence level.

A binary sampling flow analysis system equipped with gas diffusion cell was developed for NH4+ and/or NH2Cl determination in wastewater and disinfection products samples based on the Berthelot reaction of the NH2Cl diffused through the semi-permeable PTFE membrane. The effect of the analytical conditions related to the reaction and flow parameters were evaluated and N-NH4+ and N-NH2Cl were determined in concentration ranges from 0.17 to 5 mg L-1 and from 0.5 to 14.5 mg L-1, respectively. Limits of detection (3σ) of 50 and 140 µg L-1 for N-NH4+ and N-NH2Cl were calculated, respectively, and RSD of 5 and 2% were calculated for 10 consecutive determinations of N-NH4+ (1 and 3 mg L-1) and N-NH2Cl (3 and 9 mg L-1), respectively with 30 determinations h-1.

No presente trabalho foram avaliados os processos sortivos dos íons Cd2+ e Pb2+ em carne bovina em pH 6. Uma válvula de seleção de 8 canais foi utilizada para a mecanização do preparo das amostras e as concentrações de cádmio e chumbo foram determinadas por ICP-OES. Observou-se alta retenção (> 80%, m/m) dos íons Cd2+ e Pb2+ em carne fresca ou putrefata, indicando os riscos associados ao consumo de carne inadequadamente abatida, manipulada, estocada e/ou comercializada. Ácido acético a 1% (v/v) disponibilizou 70% do cádmio inicialmente adsorvido nas amostras de carne, revelando que práticas culinárias podem influenciar na sorção dos contaminantes.

The metal sorption capacity in fresh and rotten red meat was evaluated for Cd2+ and Pb2+ ions at pH 6 and the process involved in the studied metal retention was discussed. For the experimental set, an eight channels multi-port selection valve was employed to mechanise the sample preparation. The cadmium and lead concentrations were determined by ICP-OES. A high retention (> 80%, m/m) of Cd2+ and Pb2+ ions, in fresh and rotten bovine muscle was found, indicating the potential contamination risks related to the consumption of meat submitted to inappropriate conditions of abattoir, handling, storage and commercialisation. Seventy per cent of the cadmium was released with the immersion of meat in acetic acid at 1% (v/v), revealing that cookery practices may act on contaminant sorptive processes in meat structure.

Um dispositivo para a amostragem direta de sólidos por espectrometria de absorção atômica com chama (DSA-FAAS) é proposto para a determinação de chumbo em água, após o procedimento de extração em fase sólida. Uma solução tampão, NH4Cl-NH3, pH 8,1, e a fase sólida (vermelho de alizarina adsorvido em naftaleno) foram adicionados a amostra de água para adsorção de chumbo. Posteriormente, as amostras (até 200 mL) foram filtradas e a matriz de naftaleno foi seca, moída, até as partículas atingirem tamanho inferior a 80 µm e então mantida em dessecador até a determinação de Pb por DSA-FAAS. Amostras sólidas (de 0,1 a 2 mg) foram pesadas em recipientes de polietileno, os quais foram conectados ao dispositivo para introdução direta de sólidos na chama do tipo ar + acetileno. As amostras sólidas foram transportadas na forma de um aerossol seco até uma cela de quartzo em forma de "T" que foi acoplada ao queimador e posicionada entre este e o feixe óptico do espectrômetro de absorção atômica. Na chama, o vapor atômico gerado produziu um sinal transiente que era totalmente integrado em 2 s. O efeito das condições operacionais sobre o sinal analítico foi avaliado. Sinais de fundo foram sempre baixos (lambda = 217,0 nm) e não foram observados efeitos de memória. A massa característica foi de 1,1 ng de Pb. a calibração foi feita empregando-se diferentes massas de naftaleno impregnado com vermelho de alizarina, tratadas com soluções de referência de Pb. Os resultados foram considerados satisfatórios para concentrações de 30 e 50 µg L-1, tanto com respeito à exatidão (recuperações de 94 a 103%) como à precisão (desvio padrão relativo inferior a 5%, n=6). A estabilidade de Pb na fase sólida (naftaleno + vermelho de alizarina) foi avaliada até 45 dias e os resultados mostraram que o material sólido, após adsorção de Pb e secagem) pode ser armazenado durante este período. O dispositivo proposto, usado para a introdução de amostras sólidas no atomizador, pode ser acoplado facilmente a equipamentos convencionais para espectrometria de absorção atômica.

A device for direct solid analysis by flame atomic absorption spectrometry (DSA-FAAS) with prior solid phase extraction procedure is proposed for the determination of lead in water samples. A buffer solution (NH4Cl-NH3, pH 8.1) and alizarin red - naphthalene solid phase were added for Pb sorption. After, samples (up to 200 mL) were filtered and the naphthalene matrix was dried, ground to particle size < 80 µm and then maintained into a desiccator up to the Pb determination by DSA-FAAS. Test samples (from 0.1 to 2 mg) were weighed into small polyethylene vials. Vials were connected to a homemade device for solid introduction directly into a conventional air + acetylene flame. Test samples were carried as a dry aerosol to a T-quartz cell specially designed for DSA-FAAS. The T-quartz cell was positioned above the burner and below the optical path of the instrument. In the flame, the generated atomic vapor produced a transient signal that was totally integrated in 2 s. The effect of operating conditions on the analytical signal was evaluated. Background signals were always low (wavelength=217.0 nm) and no memory effects were observed. A characteristic mass of 1.1 ng for Pb was found. Calibration was performed using different masses of solid alizarin red-naphthalene spiked with Pb reference solution. Results were considered satisfactory, for concentration ranging from 30 and 50 µg L-1, regarding to both accuracy (recoveries from 94 to 103%) and precision (relative standard deviation less than 5%, n=6). The stability of lead in the solid phase (naphthalene + alizarin red) was evaluated up to 45 days and the results showed that the solid material could be stored during this period. The proposed device used for solid introduction into the flame atomizer may be easily fitted to conventional atomic absorption spectrometers.

Neste trabalho foram enfatizadas as potencialidades da geração sonoquímica de reagentes pela irradiação ultra-sônica de resíduos de organoclorados de efluentes laboratoriais com a produção de soluções de cloreto e hipoclorito para propósitos analíticos. Foi avaliada a dependência entre a produção de cloreto obtida pela sonicação de efluentes contendo organoclorados e o tempo de irradiação para CCl4, CHCl3, CH2Cl2 e do inseticida Thiamethoxam®. Sob condições de saturação pôde ser observada a maior produção de cloreto para CHCl3. O processo sonoquímico de geração de cloreto mostrou boa precisão (RSD < 10%). A extensão da geração sonoquímica de hipoclorito foi também avaliada quando conduzida em presença de concentrações diferentes de NaOH. O hipoclorito gerado pela degradação de resíduos foi monitorado pelo método de Berthelot, empregado para a determinação de NH4+. Os resultados da produção de azul de indofenol obtidos com soluções de hipoclorito geradas sonoquimicamente foram comparados, para diferentes concentrações de NH4+, com solução comercial do reagente e nenhuma diferença significativa (nível de confiança de 95%) foi constatada.

This work was aimed at highlighting the potentialities of the reagent generation by ultrasonic irradiation to produce chloride and hypochlorite solutions for analytical purposes derived from the residues of organochlorines of laboratory effluents. The dependence between the production of chloride obtained from the sonication of effluents containing organochlorines and the irradiation time was evaluated for CCl4, CHCl3, CH2Cl2 and Thiamethoxam®. It was observed that under saturation conditions the production of chloride was highest for CHCl3. Additionally, good precision related to the sonochemical generation of chloride was achieved (RSD < 10%). The extent of sonochemical generation of hypochlorite was also evaluated in the presence of different NaOH concentrations. The hypochlorite generated by the degradation of CCl4 residues was monitored by the reference Berthelot method for NH4+ determination. The results obtained with hypochlorite solution sonochemically generated for different NH4+ concentration were compared with the conventional reagent and no significant difference (95% confidence level) was found.

Um sistema de análise por injeção sequencial (SIA) foi proposto para a determinação de aldeídos totais em amostras de álcool combustível. O procedimento foi baseado na reação dos aldeídos alifáticos com o 3-metil-2-benzotiazolona hidrazona (MBTH), levando à formação de um composto azul em presença de Fe3+. As estratégias de monossegmentação e amostragem binária foram empregadas para aumentar a sensibilidade do método. A taxa de reação entre o MBTH e aldeídos foi aumentada pelo aquecimento da zona da amostra, inserindo a bobina de reação na cavidade de um forno de microondas doméstico. A faixa linear de trabalho foi entre 0,3 e 6 mg L-1 e o desvio padrão relativo foi inferior a 2,5% em todas determinações. O limite de detecção calculado foi de 60 mig L-1. Os resultados do método proposto concordaram com os obtidos por 2,4-DNPH-CLAE. Nas condições otimizadas o procedimento proposto possibilitou a determinação de até 10 amostras por hora.

A sensitive SIA method was developed for total aldehyde determination in automotive fuel ethanol samples. It was based on the selective reaction of aliphatic aldehydes with 3-methyl-2-benzothiazolone hydrazone (MBTH) with the formation of blue dye in the presence of Fe3+. Monosegmentation and binary sampling were employed to increase the sensitivity of the method. In order accelerate reaction rate of MBTH and aldehyde a mixing coil was inserted into a microwave oven cavity were the sample zone was homogeneously heated. The linear range was 0.3-6 mg L-1 with a precision, expressed as relative standard deviation, lower than 2.5% and detection limit of 60 mug L-1. The method has been successfully applied to the determination of total aldehydes in fuel ethanol and the results agreed with those obtained with 2,4-DNPH-HPLC. In the optimal condition the system can carry out 10 samples per hour.

In this work two procedures were proposed for analytical curves construction using a single standard solution employing a flow injection system with solid phase spectrophotometric detection (FI-SPS). A flow cell contends the chromogenic reagent 1-(2-tiazolylazo)-2-naphtol was positioned on the optical path. The first procedure was based on controlled concentration of analyte on solid phase and the relations between absorbance and the total volume of injected allowed the calculation of analyte concentration. The second procedure was developed employing controlled dispersion/retention in flow system where analyte concentration was obtained by exploiting the relation between transient signals of samples and single standard solution at equivalent reading time. The procedures were successfully applied for zinc determination in synthetic solutions with good precision and accuracy at 95% confidence level.

Neste trabalho a capacidade de geração de reagentes em sistemas assistidos por ultra-som é apresentada e avaliada para a oxidação de cromo e a formação de arsina. Os processos envolvidos na formação de radicais livres produzidos em soluções aquosas pela ação sonoquímica foram avaliados. A sonicação de solução aquosa de CCl4 leva à formação de radicais cloro, enquanto que a irradiação da água na presença de zinco metálico leva à produção de hidrogênio. O baixo desvio padrão relativo dos procedimentos propostos indica que o método pode ser aplicado para propósitos analíticos.

In this work, the potential of reagent generation assisted by ultrasonic irradiation was evaluated for Cr(III) oxidation and arsine formation. Free radical formation by sonolysis of aqueous solutions was evaluated. The sonication of an aqueous solution saturated with CCl4 leads to chlorine radical formation while the irradiation of water in the presence of metallic zinc leads to hydrogen production. The low relative standard deviations of the proposed procedures indicate that the method can be applied for analytical purposes.

In this work the CCl4 degradation in aqueous solution by sonication with 40 kHz commercial ultrasonic bath was investigated. Sonochemical degradation of CCl4 occur by the cleavage of C-Cl bond into the cavitation bubbles. Oxidation reactions and the pH decreasing in the bulk solution during sonication were attributed to chlorine radicals produced by CCl4 sonolysis, leading to increase the chloride concentration. The formation of oxidizing agents was evaluated employing I- and Fe2+ ion solutions, converted to I2 and HIO, and Fe3+, respectively. The amount of chloride and hydronium ions produced after 3 min of irradiation was 11.52 and 12.19 mmol, respectively, suggesting that the same reaction was involved to produce these ions. Fe2+ oxidation and the pH variation were monitored to estimate chlorine radical formation rate in the presence (0.107 mumol s-1) and absence (0.092 mumol s-1) of metallic ion during the first minute of sonication.

Com o emprego de um método simples e rápido, são propostas algumas condições de otimização para a obtenção de máxima intensidade de cavitação em banhos de ultra-som. Os parâmetros estudados foram: volume de água dentro do banho, temperatura, concentração de detergente, posição vertical e horizontal dos tubos no banho, número de tubos dentro do banho, tempo de sonicação e substituição da água do banho. Os resultados obtidos para os banhos de ultra-som estudados (Neytech e Cole-Parmer) permitiram estabelecer as seguintes condições para máxima intensidade de cavitação: 1 L de água à temperatura ambiente; 0,2 % (v/v) de detergente; posição central e ao fundo do banho. Somente 1 tubo deve ser usado por vez dentro do banho durante a aplicação do ultra-som. A intensidade de cavitação foi linear com o tempo de sonicação até 10 minutos e a substituição de água durante a sonicação melhorou a reprodutibilidade. Esse sistema de troca contínua de água permite a sonicação de até 6 amostras consecutivamente sem mudanças no volume total de água.

Optimisation conditions for obtaining maximum cavitation intensity in ultrasonic baths are proposed using a simple and fast method. Parameters such as water volume, temperature, detergent concentration, horizontal and vertical positions, number of tubes in the bath, sonication time and bath water substitution were studied. The results obtained for both baths studied (Neytech and Cole-Parmer) lead to the following conditions for maximum cavitation intensity: 1 L of water at room temperature, 0.2 % (v/v) of detergent, central position on the bottom of the tank. Only one tube at a time should be used inside the bath during the ultrasound application. The cavitation intensity was linear with the sonication time up to 10 minutes and the water substitution during the sonication improved reproducibility. This system using continuous water change makes possible the sonication of 6 consecutive samples, without changes in the water volume.

A simple and low cost flow cell is proposed for measurements by solid-phase spectrophotometry employing a conventional spectrophotometer. The flow cell geometry allows the employment of a large amount of the solid support without causing both excessive attenuation of the radiation beam and increasing of the back-pressure. The adaptation of the flow cell in the optical path of the spectrophotometer in order to increase the precision is discussed. The flow cell characteristics were demonstrated by measurements of Co(II), employing 1-(2-tiazolylazo)-2-naphthol (TAN) immobilized on C18 bonded silica as solid support. The apparent molar absorptivity and coefficient of variation were estimated as 1.86 x 10(5) L mol-1 cm-1 and 1.4 % (n=15). A sample throughput of 40 determinations per hour and a detection limit of 15 mug L-1 (99.7 % confidence level) were achieved.

A flow system procedure for spectrophotometric determination of ascorbic acid in drugs based on [Fe3+(SCN-)n]+3-n complex decomposition by reduction is described. The flow network was constituted by a set of three-way solenoid valves, controlled by a microcomputer running a software wrote in QuickBasic 4.5 language. The feasibility of the procedure was ascertained by determining ascorbic acid in drug samples with mass ranging from 0.0018 up to 0.0180 g. The results showed an agreement of about 7% when compared with recommended method. Other profitable features such as a standard deviation of 1.5% (n = 7) and a throughput of 120 determinations per hour was also achieved.