Papers by Jez Willian B Braga
Chemometrics and Intelligent Laboratory Systems, Feb 1, 2010
Bilinear least squares (BLLS) and unfold partial least squares (UPLS) are second-order multivaria... more Bilinear least squares (BLLS) and unfold partial least squares (UPLS) are second-order multivariate calibration methods, which require the application of the residual bilinearization (RBL) algorithm to achieve the second-order advantage. The present work presents a study of the choice of the number of RBL factors, in BLLS and UPLS models, for two different datasets based on fluorescence and flow injection
Journal of Agricultural and Food Chemistry, 2007
Practical implementation of multivariate calibration models has been limited in several areas due... more Practical implementation of multivariate calibration models has been limited in several areas due to the requirement of appropriate development and validation to prove their performance to standardization agencies. Herein, a detailed description of the application of multivariate calibration based on partial least-squares regression models (PLSR) for the determination of soluble solids (BRIX), polarizable sugars (POL), and reducing sugars (RS) in sugar cane juice, based on near infrared spectroscopy (NIR), for the alcohol industries is presented. The development of the models, including variable selection and outlier elimination, and their validation by determination of figures of merit, such as accuracy, precision, sensitivity, analytical sensitivity, prediction intervals, and limits of detection and quantification, are described for a representative data set of 1381 sugar cane samples. Values estimated by PLSR are compared with appropriate reference methods, where the results indicated that the PLSR models can be used in the alcohol industry as an alternative to refractometry and lead clarification before polarization measurements (standard methods for BRIX and POL, respectively). For RS, the results of a titration reference method were compared with the PLSR estimates and also with an estimate based on BRIX and POL values, as actually used in the alcohol industry. The PLSR method presented a better agreement with the titration method. However, the results indicated that the RS estimates from both PLSR and those based on the BRIX and POL values, actually used, should be improved to a safe determination of RS.
Spectrochimica Acta Part B Atomic Spectroscopy, Oct 1, 2009
Laser Induced Breakdown Spectroscopy (LIBS) is applied to evaluate the potential of this techniqu... more Laser Induced Breakdown Spectroscopy (LIBS) is applied to evaluate the potential of this technique for characterizing trace element ratios (particularly Mg/Ca and Sr/Ca) in the speleothems (cave deposits of calcium carbonate such as stalagmites) that are commonly used to reconstruct time series of past climate change. These geological materials are characterized by a relatively simple internal stratigraphy that reflects their growth history and geochemical changes through that history can reflect variability in environmental parameters such as temperature and rainfall. In this paper, the characterization of methodological and experimental parameters such as sample preparation, microsample size and representativity, sensitivity, linearity, and replicability reveals the high potential of the technique and show clear advantages versus other commonly-used techniques. ______________________________________________________________ A. Marín-Roldan et al., Evaluation of Laser Induced Breakdown Spectroscopy (LIBS) for detection of trace element variation through stalagmites: potential for paleoclimate series reconstruction
Journal of Chromatography a, May 4, 2007
The models parallel factor analysis (PARAFAC) and the recently introduced bilinear least squares ... more The models parallel factor analysis (PARAFAC) and the recently introduced bilinear least squares (BLLS) were applied to develop second-order calibration methods to high performance liquid chromatography with diode array detection (HPLC-DAD) data, where overlap of interferences with the compounds of interest was observed, making the determination and resolution of the analytes possible. In this work, the simultaneous determination of five pesticides and two metabolites in wine samples by HPLC-DAD was performed, using the second-order advantage. The results of two chromatographic methods were compared, involving either isocratic or gradient elution. An appropriate preprocessing method was necessary to correct the effects of time shifts, baseline variations and background. BLLS presented results that were of the same quality as PARAFAC in five cases, but in two other situations only PARAFAC enabled analyte quantitation. Relative errors of prediction lower than 10% for all compounds were obtained, indicating that the methodology employing HLPC-DAD and second-order calibration can handle complex analytical systems.
Ciência Florestal, 2011
Amostras de madeiras de marupá (Simarouba amara) e andiroba (Carapa guianenis) foram submetidas a... more Amostras de madeiras de marupá (Simarouba amara) e andiroba (Carapa guianenis) foram submetidas ao ataque dos fungos Trametes versicolor (podridão branca) e Gloeophylum trabeum (podridão parda). A colorimetria foi empregada para determinar as cores das madeiras antes e após o ataque dos fungos. Para acompanhar a variação do teor dos compostos químicos foi utilizada a técnica de espectroscopia de refletância difusa no infravermelho médio. Ambas as espécies foram consideradas não resistentes ao fungo de podridão branca. Para o fungo de podridão parda, a andiroba foi considerada resistente e o marupá não resistente. Ambas as espécies de madeira se apresentaram mais escuras após o ataque do fungo Gloeophyllum trabeum. Já o ataque do fungo Trametes versicolor causou clareamento na madeira da andiroba e escureceu ligeiramente o marupá. Os resultados da análise dos espectros de infravermelho mostraram que em ambas as espécies de madeira houve redução na intensidade das bandas de celulose, hemiceluloses e lignina após o ataque do Trametes versicolor, e redução somente na intensidade da banda de celulose após o ataque do Gloeophyllum trabeum. Palavras-chave: biodeterioração; podridão parda; podridão branca; técnicas não destrutivas.
Microchemical Journal, 2013
ABSTRACT This work developed and validated a new multivariate diffuse reflectance near infrared m... more ABSTRACT This work developed and validated a new multivariate diffuse reflectance near infrared method for direct determination of hydrochlorothiazide in powder pharmaceutical samples. The best partial least squares (PLS) model was obtained in the spectral region from 1640 to 1780 nm, with mean centered data preprocessed by first derivative and Savitzky–Golay smoothing followed by vector normalization. This model was built with 4 latent variables and provided a root mean square error of prediction of 1.7%. The method was validated according to the appropriate regulations in the range from 21.25 to 29.00 mg of hydrochlorothiazide per 150 mg of powder (average mass tablet), by the estimate of figures of merit, such as accuracy, precision, linearity, analytical sensitivity, capability of detection, bias and residual prediction deviation (RPD). The concept of net analyte signal (NAS) was used to estimate some figures of merit and to plot a pseudo-univariate calibration curve. The results for determinations in powdered manufactured tablets were in agreement with those of the official high performance liquid chromatographic method (HPLC). Finally, the method was extrapolated for determinations in intact tablets, providing prediction errors smaller than ± 9%. The developed method presented the advantage of being about fifteen times faster than the reference HPLC method.
Química Nova, 2009
Recebido em 25/6/08; aceito em 15/12/08; publicado na web em 28/5/09 STATE OF THE ART OF FIGURES ... more Recebido em 25/6/08; aceito em 15/12/08; publicado na web em 28/5/09 STATE OF THE ART OF FIGURES OF MERIT IN MULTIVARIATE CALIBRATION. The validation of an analytical procedure must be certified through the determination of parameters known as figures of merit. For first order data, the acuracy, precision, robustness and bias is similar to the methods of univariate calibration. Linearity, sensitivity, signal to noise ratio, adjustment, selectivity and confidence intervals need different approaches, specific for multivariate data. Selectivity and signal to noise ratio are more critical and they only can be estimated by means of the calculation of the net analyte signal. In second order calibration, some differentes approaches are necessary due to data structure.
Microchemical Journal, 2014
The analysis of inks in paper represents an important area in forensic science, since it can be u... more The analysis of inks in paper represents an important area in forensic science, since it can be used to identify possible falsifications and changes in a document. However, most of the instrumental methods proposed in the literature do not allow a nondestructive analysis of cursive writing texts, which represent a serious limitation in document examination. This paper proposes the application partial least squares for discriminant analysis (PLS-DA) and visible spectrometer measurements obtained by the Video Spectral Comparator (VSC6000®) for the nondestructive identification of blue pen inks of different types and brands in cursive handwriting texts for forensic applications. The method was developed based on twenty-five brands of inks from different blue pens. Standard samples were prepared to simulate the characteristics of the cursive handwriting. Reflectance spectra were recorded at different positions along a written line for each type and pen brand. The calibration set was optimized by the elimination of outliers and bias corrections. Two independent models were developed, the first one for identification of the pen type and the second one for brand identification. PLS-DA models presented mean prediction errors ranging from 0.03 to 0.11, which allowed the correct classification of all pen types and brands studied. The method showed to be robust in relation to different paper types and batches of pens. The analysis of a blind test indicates that the method is also free of biased judgments of the analyst and robust regarding the handwriting of different individuals. The application in a real forensic case enabled one to conclude that two ink strokes of different pages of a questioned document were written with the same pen type and brand.
Journal of the Brazilian Chemical Society, 2014
A análise de tintas é realizada para verificar a ocorrência de falsificações em documentos. Nesse... more A análise de tintas é realizada para verificar a ocorrência de falsificações em documentos. Nesse aspecto, métodos espectroscópicos são atrativos, pois preservam a integridade do documento. Neste trabalho, é proposto um método para a discriminação de tintas de canetas pretas entre tipos, marcas e modelos para a aplicação em documentos. Espectros de reflectância na região visível foram obtidos através do equipamento comparador espectral de vídeo VSC ® 6000 e da análise discriminante por mínimos quadrados parciais (PLS-DA). O método foi validado com dados independentes e um teste cego. O viés presente nos resultados foi corrigido para a detecção das amostras anômalas. Os modelos PLS-DA apresentaram baixos erros médios quadráticos de previsão (RMSEP) e permitiram a discriminação de todas as tintas de forma rápida, não destrutiva e eficiente. O método se mostrou exato e robusto com respeito a escrita de diferentes indivíduos e capaz de identificar o tipo, a marca e o modelo de caneta em um caso forense. The analysis of inks is performed to verify the occurrence of forgery in documents. Spectroscopic methods are attractive techniques for use in forensic document analysis as they, in most instances, preserve the integrity of the document. In this work, it is proposed a discrimination method of black pen inks of different types, brands and models for application in cursive handwriting. The visible reflectance spectra was obtained by the video spectral comparator VSC ® 6000 and discrimination analysis performed by partial least squares (PLS-DA). The method was validated with an independent test set and with a blind test. The bias in the results was corrected for the outlier identification. The PLS-DA models presented low root mean squared error of predictions (RMSEPs) and allowed a fast, non-destructive and an efficient discrimination of all pen inks evaluated. The method has proved to be accurate and robust regarding the handwriting of different individuals and capable of identifying the pen type, brand and pen model in a forensic case.
Journal of the Brazilian Chemical Society, 2014
A determinação do teor de cocaína em amostras de drogas consiste em uma importante tarefa em órgã... more A determinação do teor de cocaína em amostras de drogas consiste em uma importante tarefa em órgãos como a Polícia Federal Brasileira (BFP). Nesse sentido, este trabalho propõe apresentar um método baseado em espectros de infravermelho obtidos por refletância total atenuada (ATR) e regressão por mínimos quadrados parciais (PLSR) para quantificar cloridrato de cocaína em amostras de drogas. O método foi desenvolvido e validado com 275 amostras reais de drogas apreendidas pela BFP em todo o Brasil. A determinação foi realizada no intervalo de 35 a 99% (m/m) de cocaína nas amostras. Os resultados indicaram que o método é capaz de analisar diretamente amostras de drogas contendo cocaína na forma de cloridrato sem necessidade de qualquer preparo de amostra com erros médios de aproximadamente 3,00%, precisão de 1,50% (m/m) e concentração mínima detectável de 13% (m/m). The determination of cocaine in drug samples is an important task for law enforcement agencies such as the Brazilian Federal Police (BFP). In this sense, this paper proposes a method based on infrared spectra obtained by attenuated total reflectance (ATR) and partial least squares regression (PLSR) to quantify cocaine hydrochloride in drug samples. The method was developed and validated with 275 actual samples of drugs seized by the BFP. The determination was performed between 35 to 99% (m/m) of cocaine in the drug samples. Results indicate that the method is able to directly analyze drug samples containing cocaine in its hydrochloride form without any sample preparation with average prediction errors of 3.00% (m/m), 1.50% (m/m) precision and 13% (m/m) of minimum detectable concentration.
Talanta, 2012
This paper proposes a new method for determination of amoxicillin in pharmaceutical suspension fo... more This paper proposes a new method for determination of amoxicillin in pharmaceutical suspension formulations, based on transflectance near infrared (NIR) measurements and partial least squares (PLS) multivariate calibration. A complete methodology was implemented for developing the proposed method, including an experimental design, data preprocessing by using multiple scatter correction (MSC) and outlier detection based on high values of leverage, and X and Y residuals. The best PLS model was obtained with seven latent variables in the range from 40.0 to 65.0 mg mL −1 of amoxicillin, providing a root mean square error of prediction (RMSEP) of 1.6 mg mL −1. The method was validated in accordance with Brazilian and international guidelines, through the estimate of figures of merit, such as linearity, precision, accuracy, robustness, selectivity, analytical sensitivity, limits of detection and quantitation, and bias. The results for determinations in four commercial pharmaceutical formulations were in agreement with the official high performance liquid chromatographic (HPLC) method at the 99% confidence level. A pseudo-univariate calibration curve was also obtained based on the net analyte signal (NAS). The proposed chemometric method presented the advantages of rapidity, simplicity, low cost, and no use of solvents, compared to the principal alternative methods based on HPLC.
Packaging Technology and Science, 2010
The performance of oxygen scavengers can be infl uenced by several conditions, such as temperatur... more The performance of oxygen scavengers can be infl uenced by several conditions, such as temperature (T) and relative humidity (RH), which are considered to be the two major factors. Therefore, the development of new scavengers requires the study of their performance, with these conditions varied. In this paper, the response surface methodology (RSM) was used to study the performance of a newly developed oxygen scavenger sachet and to model the infl uences of T and RH and their interaction on the absorption capacity and rate constant of the developed sachet. Commercial oxygen scavenger sachets were used for comparison purposes. The oxygen absorption capacity and rate constant were evaluated with a 2 2 factorial design with a central point. The results showed that each absorber sachet presented a different behaviour and there were signifi cant interactions between T and RH; so, the RSM was the most appropriate for these studies. The developed sachet presented a better performance compared with the commercial ones at 23°C and 53% RH, which represents the condition for commercialization at room temperature of foods of intermediary water activity, while in the extreme conditions (100% RH and 37°C) all sachets present a similar absorption capacity.
Journal of Thermal Analysis and Calorimetry, 2012
Page 1. Thermal diesel-like analysis Quality control by thermal and chemometric analysis Alexandr... more Page 1. Thermal diesel-like analysis Quality control by thermal and chemometric analysis Alexandre GS Prado • Rômulo DA Andrade • Jez WB Braga • Paulo AZ Suarez Received: 5 July 2011 / Accepted: 10 August 2011 Ó Akadémiai Kiadó, Budapest, Hungary 2011 ...
Journal of the Brazilian Chemical Society, 2007
Journal of Pharmaceutical Sciences, 2004
Polymorphism is an important property in the quality control of pharmaceutical products. In this ... more Polymorphism is an important property in the quality control of pharmaceutical products. In this regard, partial least squares regression and the net analytical signal were used to build and validate a multivariate calibration model using diffuse reflectance infrared spectroscopy in the region of 900-1100 cm(-1) for the determination of the polymorphic purity of carbamazepine. Physical mixtures of the polymorphs were made by weight, from 80 to 100% (w/w) form III mixed with form I. Figures of merit, such as sensitivity, analytical sensitivity, selectivity, confidence limits, precision (mean, repeatability, intermediate), accuracy, and signal-to-noise ratio were calculated. Feasible results were obtained with maximum absolute error of 2% and an average error of 0.53%, indicating that the proposed methodology can be used by the pharmaceutical industry as an alternative to the X-ray diffraction (United States Pharmacopoeiamethod).
Journal of Chromatography A, 2012
The current legislation requires the mandatory addition of biodiesel to all Brazilian road diesel... more The current legislation requires the mandatory addition of biodiesel to all Brazilian road diesel oil A (pure diesel) marketed in the country and bans the addition of vegetable oils for this type of diesel. However, cases of irregular addition of vegetable oils directly to the diesel oil may occur, mainly due to the lower cost of these raw materials compared to the final product, biodiesel. In Brazil, the situation is even more critical once the country is one of the largest producers of oleaginous products in the world, especially soybean, and also it has an extensive road network dependent on diesel. Therefore, alternatives to control the quality of diesel have become increasingly necessary. This study proposes an analytical methodology for quality control of diesel with intention to identify and determine adulterations of oils and even fats of vegetable origin. This methodology is based on detection, identification and quantification of triacylglycerols on diesel (main constituents of vegetable oils and fats) by high performance liquid chromatography in reversed phase with UV detection at 205 nm associated with multivariate methods. Six different types of oils and fats were studied (soybean, frying oil, corn, cotton, palm oil and babassu) and two methods were developed for data analysis. The first one, based on principal component analysis (PCA), nearest neighbor classification (KNN) and univariate regression, was used for samples adulterated with a single type of oil or fat. In the second method, partial least square regression (PLS) was used for the cases where the adulterants were mixtures of up to three types of oils or fats. In the first method, the techniques of PCA and KNN were correctly classified as 17 out of 18 validation samples on the type of oil or fat present. The concentrations estimated for adulterants showed good agreement with the reference values, with mean errors of prediction (RMSEP) ranging between 0.10 and 0.22% (v/v). The PLS method was efficient in the quantification of mixtures of up to three types of oils and fats, with RMSEP being obtained between 0.08 and 0.27% (v/v), mean precision between 0.07 and 0.32% (v/v) and minimum detectable concentration between 0.23 and 0.81% (v/v) depending on the type of oil or fat in the mixture determined.
Journal of Agricultural and Food Chemistry, 2007
Practical implementation of multivariate calibration models has been limited in several areas due... more Practical implementation of multivariate calibration models has been limited in several areas due to the requirement of appropriate development and validation to prove their performance to standardization agencies. Herein, a detailed description of the application of multivariate calibration based on partial least-squares regression models (PLSR) for the determination of soluble solids (BRIX), polarizable sugars (POL), and reducing sugars (RS) in sugar cane juice, based on near infrared spectroscopy (NIR), for the alcohol industries is presented. The development of the models, including variable selection and outlier elimination, and their validation by determination of figures of merit, such as accuracy, precision, sensitivity, analytical sensitivity, prediction intervals, and limits of detection and quantification, are described for a representative data set of 1381 sugar cane samples. Values estimated by PLSR are compared with appropriate reference methods, where the results indicated that the PLSR models can be used in the alcohol industry as an alternative to refractometry and lead clarification before polarization measurements (standard methods for BRIX and POL, respectively). For RS, the results of a titration reference method were compared with the PLSR estimates and also with an estimate based on BRIX and POL values, as actually used in the alcohol industry. The PLSR method presented a better agreement with the titration method. However, the results indicated that the RS estimates from both PLSR and those based on the BRIX and POL values, actually used, should be improved to a safe determination of RS.
International Journal of Environmental Research and Public Health, 2010
In non-ideal scenarios involving partial or non-breastfeeding, cow's milk-based dairy products ar... more In non-ideal scenarios involving partial or non-breastfeeding, cow's milk-based dairy products are mainstream in infant feeding. Therefore, it is important to study the concentrations of potentially neurotoxic contaminants (Pb and Cd) and their respective counteracting elements (Ca and Zn) in infant dairy products. Fifty-five brands of infant formulas and milk sold in Brasilia, Brazil were analyzed. The dairy products came from areas in the central-west (26%), southeast (29%) and south of Brazil (36%) extending as far as Argentina (7%) and the Netherlands (2%). For toxic Pb and Cd, median concentrations in powdered samples were 0.109 mg/kg and 0.033 mg/kg, respectively; in fluid samples median Pb concentration was 0.084 mg/kg, but median Cd concentration was below the limit of detection and overall values were below reference safety levels. However, 62% of these samples presented higher Pb concentration values than those
The Analyst, 2008
Multivariate curve resolution using alternating least squares (MCR-ALS) was used to quantify asco... more Multivariate curve resolution using alternating least squares (MCR-ALS) was used to quantify ascorbic (AA) and acetylsalicylic (ASA) acids in four pharmaceutical samples using a flow injection analysis (FIA) system with pH gradient and a diode array (DAD) spectrometer as a detector. Four different pharmaceutical drugs were analyzed, giving a data array of dimensions 51 x 291 x 61, corresponding respectively to number of samples, FIA times and spectral wavelengths. MCR-ALS was applied to these large data sets using different constraints to have optimal resolution and optimal quantitative estimations of the two analytes (AA and ASA). Since both analytes give an acid-basic pair of species contributing to the UV recorded signal, at least four components sholuld be proposed to model AA and ASA in synthetic mixture samples. Moreover, one additional component was needed to resolve accurately the Schlieren effect and another additional component was also needed to model the presence of poss...
Forensic Science International, 2012
Uploads
Papers by Jez Willian B Braga