Abstract In the present study, a new, sensitive, and rapid method was developed for extraction and determination of the trace amounts of Pb (II) and Cd (II) ions in milk samples through magnetic solid-phase extraction using DABCO based-ionic liquid-modified magnetic nanoparticles (Fe3O4/[DABCO-PDO]Cl NPs). Herein, Pb (II) and Cd (II) contents were quantified with flame atomic absorption spectroscopy (FAAS). The effect of different empirical parameters (such as sample pH, adsorbent amount, type and amount of the elution, extraction and desorption times, and the ligand concentration) was evaluated and optimized for simultaneous extraction and pre-concentration Pb (II) and Cd (II) ions. The calibration curve was linear under the optimum condition in the concentration range of 0.4-200 µgL-1 for Cd, and 0.5-120 µgL-1 for Pb, respectively. The pre-concentration factor was 67, with the detection limit of 0.09 and 0.07 µgL-1 for Pb and Cd, respectively. The relative standard deviation values (RSD %) of the proposed method were lower than 2.6 %. The developed method was successfully used to determine lead and cadmium content in milk samples. The information obtained from the method validation has been used to estimate the expanded uncertainty for the determination of Pb (II) and Cd (II) at trace levels in commercial milks.

Resumen En este trabajo, se ha desarrollado un nuevo, sensible y rápido procedimiento para la extracción y determinación de iones Pb(II) y Cd(II) a nivel de trazas en leche, mediante extracción en fase sólida utilizando nanopartículas magnéticas modificadas con líquido iónico basado en DABCO (Fe3O4/[DABCO-PDO]Cl NPs). La determinación de ambos metales se llevó a cabo por espectrometría de absorción atómica con atomización en llama. Se ha evaluado el efecto de diferentes parámetros empíricos (tales como pH, cantidad de adsorbente, tipo y cantidad de solvente de elución, tiempo de extracción y desorción, y concentración del ligando); estos parametros fueron optimizados enfocándose en la extracción y preconcentración simultanea de ambos iones. Empleando las condiciones establecidas, se obtuvo buena linealidad de las curvas de calibración en el intervalo de concentraciones 0.4-200 µgL-1 para Cd, y 0.5-120 µgL-1 para Pb, respectivamente. Se logró el factor de preconcentración 67, con los límites de detección 0.09 y 0.07 µgL-1 para Pb y Cd, respectivamente. Los valores de desviación estandar relativa (RSD %) en el procedimiento propuesto no sobrepasaron 2.6 %. En el análisis de leche, se obtuvieron resultados satisfactorios. Los datos obtenidos en etapa de validación se utilizaron para estimar la incertidumbre expandida en la determinación de Pb y Cd a nivel de trazas en leche.

Abstract This study shows that genetic algorithm (GA) is a suitable method for selecting wavelengths for partial least squares (PLS) calibration of mixtures with almost identical spectra without loss of prediction capacity employing spectrofluorimetric method. A training set of mixtures containing different concentrations of ofloxacin (OFL) and riboflavin (B2) were prepared to be used as calibration set to check the prediction ability of GA-PLS models due to spectral overlapping of these constituents. Each model was validated using a validation set and then real samples were analyzed. Linear calibration curves were obtained in the 0.5-5.0 and 2.0-10.0 µg mL-1 range for ofloxacin and riboflavin, respectively. To preprocess the data matrices, the orthogonal signal correction (OSC) was used and the analysis results were statistically compared. The methods accuracy for simultaneous determination of ofloxacin and riboflavin, were evaluated by the root mean square errors of prediction (RMSEP) which were 0.0868 and 0.158 for ofloxacin and riboflavin, respectively, and relative standard error of prediction (RSEP) which were 2.738 and 2.846 for ofloxacin and riboflavin, respectively using OSC-GA-PLS models. This procedure allows the simultaneous determination of OFL and B2 in human urine and serum samples with good reliability of the determination.

Resumen. En este estudio se muestra que los algoritmos genéticos (GA) son un método adecuado para seleccionar longitudes de onda para calibrar métodos de mínimos cuadrados parciales (PLS) de mezclas, con espectros casi idénticos sin perder la capacidad de predicción al utilizar el método espectrofluorimétrico. Se preparó un conjunto de entrenamiento de mezclas que contenían diferentes concentraciones de ofloxacina (OFL) y riboflavina (B2), que se usaron como un conjunto de calibración, para verificar la capacidad predictiva de los modelos GA-PLS debidos a la superposición espectral de estos componentes. Cada modelo se comprobó usando un conjunto de validación y, posteriormente, las muestras reales se analizaron. Se obtuvieron curvas de calibración lineal en los intervalos de 0.5-5.0 y 2.0-10.0 µg mL-1, para ofloxacina y riboflavina, respectivamente. Para el preprocesamiento de las matrices de datos, se utilizó la corrección ortogonal de señal (OSC) y los resultados del análisis se compararon estadísticamente. La precisión de los métodos para la determinación simultánea de ofloxacina y riboflavina se evaluó mediante la predicción de los errores cuadráticos medios (RMSEP) que fueron 0.0868 y 0.158 para ofloxacina y riboflavina, respectivamente, y la predicción del error relativo estándar (RSEP) que fueron 2.738 y 2.846 para ofloxacina y riboflavina, respectivamente, utilizando los modelos OSC-GA-PLS. Este procedimiento permite la determinación simultánea de OFL y B2 en orina humana y en muestras de suero con buena confianza en su determinación.

Abstract: The electrochemical behavior of Bi+3 ions on the surface of a glassy carbon electrode, in acidic media and in the presence of tamoxifen, was investigated. Cyclic voltammetry, chronoamperometry, differential pulse voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy were used to find the probable mechanism contributing to the reduction of the peak height of bismuth oxidation with an increase in the concentration of tamoxifen. The obtained results show a slight interaction between the bismuth species and tamoxifen which co-deposit on the surface of glassy carbon electrode. Therefore, the reduction in the peak height of bismuth oxidation as a function of tamoxifen concentration was used to develop a new differential pulse anodic striping voltammetry method for determination of trace amount of tamoxifen. The effects of experimental parameters on the in situ DPASV of Bi+3 ions in the presence of tamoxifen shown the optimal conditions as: 2 mol L-1 H2SO4 (1% v v-1 MeOH), a deposition potential of -0.5 V, a deposition time of 60 s, and a glassy carbon electrode rotation rate of 300 rpm. The calibration curve was plotted in the range of 0.5 to 6 µg mL-1 and the limits of detection and quantitation were calculated to be 3.1 × 10-5 µg mL-1 and 1.0 × 10-4 µg mL-1, respectively. The mean, RSD, and relative bias for 0.5 µg mL-1 (n=5) were found to be 0.49 µg mL-1, 0.3%, and 2%, respectively. Finally, the proposed method was successfully used for the determination of tamoxifen in serum and pharmaceutical samples.

Resumen: Se investigó el comportamiento electroquímico de los iones Bi+3 en la superficie de un electrodo de carbono vítreo, en medios ácidos y en presencia de tamoxifeno. Se utilizaron voltametría cíclica, cronoamperometría, voltametría diferencial de pulso, espectroscopia de impedancia electroquímica y microscopía electrónica de barrido con espectroscopia de rayos X de dispersión de energía con el aumento de la concentración de tamoxifeno. Los resultados obtenidos muestran una ligera interacción entre las especies de bismuto y el tamoxifeno que se depositan conjuntamente en la superficie del electrodo de carbono vítreo. Por lo tanto, la reducción en la altura máxima de la oxidación de bismuto en función de la concentración de tamoxifeno se utilizó para desarrollar un nuevo método de voltametría de banda anódica de pulso diferencial para la determinación de la cantidad de traza de tamoxifeno. Los efectos de los parámetros experimentales en el DPASV in situ de iones Bi+3 en presencia de tamoxifeno mostraron las condiciones óptimas como: 2 mol L-1 H2SO4 (1% v v-1 MeOH), un potencial de deposición de -0.5 V, un tiempo de deposición de 60 s, y una velocidad de rotación del electrodo de carbono vítreo de 300 rpm. La curva de calibración se trazó en el rango de 0.5 a 6 µg mL-1 y los límites de detección y cuantificación se calcularon en 3.1 × 10-5 µg mL-1 y 1.0 × 10-4 µg mL-1, respectivamente. Se encontró que la media, la RSD y el sesgo relativo para 0.5 µg mL-1 (n = 5) eran 0.49 µg mL-1, 0.3% y 2%, respectivamente. Finalmente, el método propuesto se utilizó con éxito para la determinación de tamoxifeno en muestras de suero y farmacéuticas.

Dispersive liquid-liquid microextraction (DLLME) and spectrofluorimetry, coupled with chemometrics methods, are proposed in this work for the pre-concentration and determination of ofloxacin concentration in spiked human urine. Chloroform and acetonitrile were selected as the extraction and dispersive solvents by the one-variable-at-a-time process. The Box-Behnken design was used to optimize the other variables, including the volume of extraction and dispersion solvents, solution pH, and ionic strength. A linear calibration curve was obtained in the 5.0-120.0 ng mL-1 range under optimal conditions with a detection limit of 1.61 ng mL-1 and correlation coefficient of 0.9948. A relative standard deviation (RSD) of 1.13% was obtained for seven consecutive replicates. Parallel factor analysis (PARAFAC) and partial least square (PLS) modeling were applied for the multivariate calibration of the spectrofluorimetric data. To pre-process the data matrices and predict the model results, the orthogonal signal correction (OSC) was used, and the analysis results were statistically compared. The methods accuracy values for ofloxacin determination, evaluated by the root mean square errors of prediction (RMSEP) and relative standard error of prediction (RSEP), were 0.82 and 1.12 using OSC-PLS, and 0.31 and 0.42 using OSC-PARAFAC models, respectively. Ofloxacin can be reliably determined in human urine samples through the proposed procedure, according to the results.

In this study, a highly sensitive and reliable microextraction method, known as in tube ultrasonic and air assisted liquid-liquid microextraction (IT-UAA-LLME), was developed for the preconcentration of some phthalate esters, such as dimethyl phthalate, diethyl phthalate (DEP), di-butyl-phthalate (DBP), bis(2-ethylhexyl) phthalate (BEHP), butyl benzyl phthalate (BBP), and di n-octyl-phthalate (DNOP), prior to their determination using gas chromatography-mass spectrometry (GC-MS). In this technique, the extraction solvent was dispersed into the aqueous sample solution using an ultrasonic bath. The effects of solvent type, aeration time and salt concentration were investigated. After extraction, an organic solvent was injected into the GC-MS instrument for quantification. Under optimum conditions, the enrichment factors ranged from 100 to 330. The calibration curves showed good linearity (r2 > 0.99) and limit of detections were obtained in the range of 0.1-2.1 ng mL-1 in the working concentration ranges. The method was successfully applied for determination of six phthalate esters in real samples with complex matrices with relative standard deviation less than 8%, recovery 88-112% and thus, satisfactory results were obtained.

In this study, a novel method based on floatation assistance of homogeneous liquid-liquid microextraction (FA-HLLME), combined with inductively coupled plasma-mass spectroscopy (ICP-MS) was proposed, for the determination of trace uranium in environmental water samples. As one of the miniaturized separation and extraction techniques, homogenous liquid-liquid microextraction (HLLME) has been widely applied in the field of environmental monitoring and assessment. 1,2-pyridylazo-2-naphthol (PAN) was used as the complexing agent while toluene and methanol were selected as the extraction and homogeneous solvents, respectively. The factors that influenced the extraction efficiency for uranium determination (including pH, extraction and homogeneous solvents, concentration of PAN and NaCl, extraction time) were studied statistically. Under optimum conditions (pH=7.0, 100 μL toluene, 500 μL methanol, 6.4×10-5 mol L-1 PAN, 1.5 mol L-1 NaCl and 60 sec of extraction time), the linear dynamic range for uranium determination was 1.0-500.0 ng L-1 (R²=0.9995), with a corresponding limit of detection (LOD) of was 0.27 ng L-1. The relative standard deviation (R.S.D.) (C=50.0 ng L-1, n=9) was 1.13%, with a corresponding enrichment factor of 360 for uranium extraction. The proposed method was successfully applied for the determination of uranium in different water samples.

Background: Newcastle disease is an important avian infectious disease that brings about vast economic damage for poultry industry. Transgenic plants represent a cost-effective system for the production of therapeutic proteins and are widely used for the production of poultry vaccines. In an attempt to develop a recombinant vaccine, a plant expression binary vector pBI121, containing the genes encoding Hemagglutinin-Neuraminidase (HN) and Fusion (F) epitopes of Newcastle Disease Virus (NDV) under the control of CaMV35S promoter and NOS terminator was constructed and introduced into the tobacco ( Nicotiana tabacum) plant by Agrobacterium-mediated transformation. Results: Putative transgenic plants were screened in a selection medium containing 50 mg/L kanamycin and 30 mg/L meropenem. Integration of the foreign gene in plant genome was confirmed by PCR. Expression of foreign gene was analyzed at transcription level by RT-PCR and at translation level by means of dot blotting and ELISA. All analyses confirmed the expression of recombinant protein. Conclusion: Developments in genetic engineering have led to plant-based systems for recombinant vaccine production. In this research, tobacco plant was used to express F and HN epitopes of NDV. Our results indicate that for the production of recombinant vaccine, it is a novel strategy to use concatenated epitopes without their genetic fusion onto larger scaffold structure such as viral coat protein.

A quantitative structure-activity relationship (QSAR) modeling was carried out for the prediction of inhibitory activity of 1-phenyl[2H]-tetrahydro-triazine-3-one analogues as inhibitors of 5-lipoxygenase. Partial least squares (PLS) algorithm was employed to model the relationships between molecular descriptors and inhibitory activity of molecules using the genetic algorithm (GA) method as variable selection tool. Pre-processing methods such as wavelet transform (WT) were also used to enhance the predictive power of multivariate calibration methods. To evaluate the models applied in this study (PLS, GA-PLS and WT-GA-PLS), the inhibitory activities of several compounds, not included in the modeling procedure, were predicted. The results of models showed high prediction ability with root mean square error of prediction 0.194, 0.161 and 0.140 for PLS, GA-PLS and WT-GA-PLS, respectively. The WT-GA-PLS method was employed to predict the inhibitory activity of the new inhibitor derivatives.

Se realizó la modelación de una relación estructura-actividad (QSAR, por su siglas en inglés) para la predicción de la actividad inhibitoria de análogos del 1-fenil[2H]-tetrahidro-triazina-3-ona como inhibidores de la 5-lipoxigenasa. Se utilizó el algoritmo de mínimos cuadrados parciales (PLS, por sus siglas en inglés) para simular las relaciones entre los descriptores moleculares y la actividad inhibitoria de moléculas, usando el método de algoritmos genéticos (GA, por sus siglas en inglés) como herramienta de selección de variables. También se utilizaron métodos de preprocesamiento como transformada de ondeleta (WT, por sus siglas en inglés) para incrementar el poder predictivo de los métodos de calibración multivariable. Para evaluar los modelos aplicados en este estudio (PLS, GA-PLS y WT-GA-PLS), se evaluaron las actividades inhibitorias de varios compuestos no incluidos en el proceso de modelación. Los resultados de los modelos mostraron una alta capacidad predictiva con un error cuadrático medio en la predicción de 0.194, 0.161 y 0.140 para PLS, GA-PLS y WT-GA-PLS, respectivamente. Se utilizó el método WT-GA-PLS para predecir la actividad inhibitoria de nuevos derivados inhibidores.

A new implemented quantitative structure-property relationships (QSPR) method, whose descriptors achieved from bidimensional images, was suggested for the predicting of acidity constant (pKa) of various acid. The resulted descriptors were subjected to principal component analysis (PCA) and the most significant principal components (PCs) were extracted. Multivariate image analysis applied to QSPR modeling was done by means of principal component-least squares support vector machine (PC-LSSVM) methods. The resulted model showed high prediction ability with root mean square error of prediction of 0.0195 for PC-LSSVM.

A new simple and rapid dispersive liquid-liquid microextraction has been applied to preconcentration trace levels of bismuth as a prior step to its determination by spectrophotometric detection. In the proposed method, dithizone was used as a chelating agent, and tetrachloride carbon and ethanol are selected as extraction and dispersive solvent. The optimization strategy is carried out by using two level full factorial designs. Results of the two level full factorial design (2(4)) based on an analysis of variance demonstrated that the pH, concentration of dithizone, amount of dispersive and extraction solvents were statistically significant. Optimal condition for four variables: pH, concentration of dithizone, amount of dispersive and extraction solvents are obtained by using Box-Behnken design. Under the optimum conditions, the calibration graphs were linear in the range of 5-300 ng mL-1 with detection limit of 1.6 ng mL-1 (3δB/m) and the enrichment factor of this method for bismuth reached at 150. The relative standard deviation (R.S.D.) is 2.3% (n = 5, c = 50 ng mL-1). The method is successfully applied to the determination of trace amount of bismuth in water samples.

Máquinas de vetor de suporte por mínimos quadrados (LS-SVM) e mínimos quadrados parciais (PLS) têm recebido atenção considerável em quimiometria para análise multicomponente. Foi realizada uma comparação entre os métodos LS-SVM e PLS aplicando-os na determinação espectrofotométrica simultânea de cipermetrina, permetrina e tetrametrina. Os espectros de absorbância no UV de soluções metanólicas foram medidas nas faixas de concentração 0,1-12,9, 0,1-24,9 e 0,1-13,8 µg mL-1 para cipermetrina, permetrina e tetrametrina, respectivamente. A determinação simultânea por espectrofotometria no UV desses analitos representa um problema em química analítica devido às interferências espectrais. Dessa forma foi realizada a resolução da mistura por métodos quimiométricos. As raízes quadradas do erro quadrático médio de previsão (RMSEP) para cipermetrina, permetrina e tetrametrina por PLS e LS-SVM foram 0,1629, 0,2828, 0,1984 e 0,0766, 0,0907, 0,0467, respectivamente. A habilidade do método para análise de amostras em matrizes sintéticas e reais apresentou resultados satisfatórios. Os dados obtidos mostraram que o LS-SVM produziu melhores resultados que o PLS.

Least-squares support vector machines (LS-SVM) and partial least squares (PLS) have received considerable attention in the chemometrics for multicomponent analysis. A comparison was made between LS-SVM and PLS methods by applying them to simultaneous spectrophotometric determination of cypermethrin, permethrin and tetramethrin. The UV absorbance spectra of the methanolic solutions of the analytes were measured in the concentration ranges, 0.1-12.9, 0.1-24.9 and 0.1-13.8 µg mL-1 for cypermethrin, permethrin and tetramethrin, respectively. The simultaneous determination of cypermetrin, permetrin and tetrametrin by UV spectrophotometry is a difficult problem in analytical chemistry, due to spectra interferences. The resolution of mixture of cypermetrin, permetrin and tetrametrin by chemometrics methods was performed. The root means square error of prediction (RMSEP) for cypermetrin, permetrin and tetrametrin by PLS and LS-SVM models were 0.1629, 0.2828, 0.1984 and 0.0766, 0.0907, 0.0467, respectively. The capability of the method for the analysis of synthesis and real matrix samples were evaluated by the determination of cypermethrin, permethrin and tetramethrin with satisfactory results. The resultant data explained that LS-SVM produced better results than PLS.

A protonação e complexação de Ni(II) por 4-(2-piridilazo) resorcinol (PAR) em força iônica 0,1 mol L-1 KNO3 a 25 ºC, foram estudadas por análise global. Em titulações espectrofotométricas, a dependência linear ou quase linear da concentração e a existência de espécies em menores concentrações podem causar dificuldades na avaliação dos dados. Espectros de absorção e as correspondentes constantes de equilíbrio calculadas ou são desconhecidos ou mal estabelecidos. Dessa forma, torna-se difícil ajustar um modelo confiável aos dados. Na análise global de segunda ordem, titulações espectrofotométricas com diferentes concentrações iniciais são simultaneamente analisadas. Assim, condições para a formação signifitiva de todas as espécies podem ser obtidas e, conseqüentemente, a matriz de concentração é completada. EQUISPEC é um programa computacional que usa matriz gerada em ambiente MATLAB para análise global de segunda ordem de dados espectrofotométricos. As titulações espectrofotométricas foram efetuadas, no mínimo, para quatro diferentes valores da razão metal-ligante.

The protonation and Ni(II) complexation of 4-(2-pyridylazo) resorcinol (PAR) in ionic strength 0.1 mol L-1 KNO3 at 25 ºC has been studied by global analysis. In spectrophotometric titrations, linear or near-linear dependence of concentration profiles and the existence of minor species can cause difficulties in the evaluation of the data. Both calculated absorption spectra and the corresponding equilibrium constants are not or only poorly defined. The result is the inability to reliably fit a reasonable model to the data. In second order global analysis, a number of spectrophotometric titrations with different initial concentrations are simultaneously analyzed. In this way, conditions for the significant formation of all species can be obtained and consequently the concentration matrix is augmented to full rank. EQUISPEC is a computer program using the matrix based MATLAB environment for second order global analysis of spectrophotometric equilibrium data. The spectrophotometric titrations were carried out at least in four different metal to ligand ratios.

The investigation of the dissociation equilibrium of Nitroso-R-Salt (NRS) in aqueous micellar solution was determined spectrophotometrically at 25°C and at the constant ionic strength I = 0.1 M KNO3. For this purpose, the effect of nonionic (Triton X-100), cationic (CTAB), and anionic (SDS) surfactants on the absorption spectra of NRS at different pH values were studied. The acidity constants of all related equilibria are estimated using the whole spectral fitting of the collected data to an established factor analysis model. The computer program DATAN was used to extract the desired information from the spectral data. The outputs of the fitting processes were acidity constant, spectral profiles of pure forms, distribution diagrams and other factor analysis data. The effects of surfactant on acidity constant and pure spectrum of each component are discussed

Um novo método espectrofotométrico, simples e sensível, foi descrito para determinação simultânea de urânio e tório. O método é baseado na formação de complexos de urânio e tório com Arsenazo III em pH 3,0. Todos os fatores que afetam a sensibilidade foram otimizados e o intervalo dinâmico linear para determinação de cada analito foi encontrado. A determinação simultânea de urânio e tório em misturas empregando métodos espectrofotométricos é dificultada pela ocorrência de interferências espectrais. Usando métodos de calibração multivariada, tais como mínimos quadrados parciais (PLS), é possível obter um modelo ajustado aos valores das concentrações das misturas usados no intervalo de calibração. A correção do sinal ortogonal (OSC) é uma técnica de pré-processamento usada para remover informações não relacionadas às variáveis alvo, empregando análise de componentes principais restrita. OSC é um método de pré-processamento adequado para a calibração PLS de misturas, sem perda da capacidade de predição, usando-se método espectrofotométrico. Neste estudo, o modelo de calibração é baseado no espectro de absorção, no intervalo de 600-760 nm para 25 diferentes misturas de urânio e tório. Matrizes de calibração foram obtidas a partir de soluções contendo 0,10-21,00 e 0,25-18,50 µg mL-1 de urânio e tório, respectivamente. Os valores de RMSEP (raiz quadrada do erro médio de predição) para urânio e tório com OSC e sem OSC foram 0,4362; 0,4183 e 1,5710; 1,0775, respectivamente. Esse procedimento possibilita a determinação simultânea de urânio e tório em amostras reais e sintéticas com adequada confiabilidade na determinação.

A simple, novel and sensitive spectrophotometric method was described for simultaneous determination of uranium and thorium. The method is based on the complex formation of uranium and thorium with Arsenazo III at pH 3.0. All factors affecting the sensitivity were optimized and the linear dynamic range for determination of uranium and thorium found. The simultaneous determination of uranium and thorium mixtures by using spectrophotometric methods is a difficult problem, due to spectral interferences. By multivariate calibration methods such as partial least squares (PLS), it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. Orthogonal signal correction (OSC) is a preprocessing technique used for removing the information unrelated to the target variables based on constrained principal component analysis. OSC is a suitable preprocessing method for PLS calibration of mixtures without loss of prediction capacity using spectrophotometric method. In this study, the calibration model is based on absorption spectra in the 600-760 nm range for 25 different mixtures of uranium and thorium. Calibration matrices contained 0.10-21.00 and 0.25-18.50 µg mL-1 of uranium and thorium, respectively. The RMSEP for uranium and thorium with OSC and without OSC were 0.4362, 0.4183 and 1.5710, 1.0775, respectively. This procedure allows the simultaneous determination of uranium and thorium in synthetic and real matrix samples with good reliability of the determination.