Multiway Calibration Strategies in Laser-Induced Breakdown Spectroscopy: A Proposal.

In this study, a new approach to laser-induced breakdown spectroscopy (LIBS) data modeling using multiway algorithms was investigated. Two case studies, parallel factor analysis (PARAFAC) and unfolded-partial least-squares with residual bilinearization (U-PLS/RBL) algorithms were used in (1) the determination of Al, Cu, and Fe in samples of reference material of printed circuit board (PCB) from electronic waste and (2) the determination of Ca, K, and Mg in samples of a human mineral supplement, where depth was used to obtain multidimensional data in the first case and delay-time in the second. In addition, univariate calibration was applied and compared with the multiway approaches. In all cases, the calibration data set was prepared from salts. PARAFAC showed satisfactory results in the first study, with low prediction errors and good accuracy for most samples, and the U-PLS/RBL algorithm presented the best performance for mineral supplement samples.

Microwave-assisted digestion using dilute nitric acid solution and investigation of calibration strategies for determination of As, Cd, Hg and Pb in dietary supplements using ICP-MS.

This study proposes an analytical procedure for microwave-assisted sample preparation of dietary supplements for athletes using dilute nitric acid solution followed by determination of elemental impurities (As, Cd, Hg and Pb) by inductively coupled plasma mass spectrometry (ICP-MS) according to the United States Pharmacopeia Chapters 2232 and 233. Calibration strategies as internal standardization (IS), multi-isotope calibration (MICal), and one-point standard addition (OP SA) were applied for correction of matrix effects. The optimization of the sample preparation procedure was performed using Doehlert experimental design based on overall desirability results (residual acidity, dissolved organic carbon and recoveries reached for certified reference material of Typical Diet) for each calibration method evaluated. Accuracy was also evaluated by recovery experiments according to the permissible daily exposure specific for each element and samples were spiked with element concentrations of 0.5J and 1.5J in order to check accuracies for As, Cd, Hg and Pb. Recoveries ranged from 82 to 120% using IS, 90 to 125% using MICal, 88 to 120% using OP SA and the repeatability was demonstrated by a precision lower than 10% RSD. Ten samples of dietary sport supplements were analyzed using the three calibration methods evaluated and the concentrations of As, Cd and Pb determined in eight samples were lower than the limits established by the Chapter 2232.

Calibration strategies for the direct determination of Ca, K, and Mg in commercial samples of powdered milk and solid dietary supplements using laser-induced breakdown spectroscopy (LIBS).

This study describes the application of laser-induced breakdown spectroscopy (LIBS) for the direct determination of Ca, K and Mg in powdered milk and solid dietary supplements. The following two calibration strategies were applied: (i) use of the samples to calculate calibration models (milk) and (ii) use of sample mixtures (supplements) to obtain a calibration curve. In both cases, reference values obtained from inductively coupled plasma optical emission spectroscopy (ICP OES) after acid digestion were used. The emission line selection from LIBS spectra was accomplished by analysing the regression coefficients of partial least squares (PLS) regression models, and wavelengths of 534.947, 766.490 and 285.213nm were chosen for Ca, K and Mg, respectively. In the case of the determination of Ca in supplements, it was necessary to perform a dilution (10-fold) of the standards and samples to minimize matrix interference. The average accuracy for powdered milk ranged from 60% to 168% for Ca, 77% to 152% for K and 76% to 131% for Mg. In the case of dietary supplements, standard error of prediction (SEP) varied from 295 (Mg) to 3782mgkg-1 (Ca). The proposed method presented an analytical frequency of around 60 samples per hour and the step of sample manipulation was drastically reduced, with no generation of toxic chemical residues.

Chromatographic profiles of Phyllanthus aqueous extracts samples: a proposition of classification using chemometric models.

Taking in consideration the global analysis of complex samples, proposed by the metabolomic approach, the chromatographic fingerprint encompasses an attractive chemical characterization of herbal medicines. Thus, it can be used as a tool in quality control analysis of phytomedicines. The generated multivariate data are better evaluated by chemometric analyses, and they can be modeled by classification methods. "Stone breaker" is a popular Brazilian plant of Phyllanthus genus, used worldwide to treat renal calculus, hepatitis, and many other diseases. In this study, gradient elution at reversed-phase conditions with detection at ultraviolet region were used to obtain chemical profiles (fingerprints) of botanically identified samples of six Phyllanthus species. The obtained chromatograms, at 275 nm, were organized in data matrices, and the time shifts of peaks were adjusted using the Correlation Optimized Warping algorithm. Principal Component Analyses were performed to evaluate similarities among cultivated and uncultivated samples and the discrimination among the species and, after that, the samples were used to compose three classification models using Soft Independent Modeling of Class analogy, K-Nearest Neighbor, and Partial Least Squares for Discriminant Analysis. The ability of classification models were discussed after their successful application for authenticity evaluation of 25 commercial samples of "stone breaker."

Evaluation of biodiesel-diesel blends quality using 1H NMR and chemometrics.

In this work, the use of (1)H NMR spectroscopy and statistical approach to the evaluation of biodiesel-diesel blends quality is described. Forty-six mixtures of oil-diesel, biodiesel-diesel, and oil-biodiesel-diesel were analyzed by (1)H NMR and such data were employed to design four predictive models. Thirty-six mixtures were used in the calibration set and the others in the validation. The PCR and PLS models were evaluated through statistical parameters. Briefly, PLS and PCR models were suitable for the prediction of biodiesel and oil concentration in mineral diesel. Specially, in higher concentration the predicted values were quite similar to the real ones. This fact was evidenced by the low relative errors of high concentrated samples; this means that the prediction of low concentrated samples will probably show high deviation. Therefore, (1)H NMR-PLS and (1)H NMR-PCR methods are fairly useful for the quality control of biodiesel-diesel blends, particularly they are suitable for prediction of concentrations greater than 2%.

Avaliação do teor de ferro e zinco e composição centesimal de farinhas de trigo e milho enriquecidas / Evaluation of iron and zinc content and centesimal composition of enriched wheat and corn flours

O objetivo deste trabalho foi avaliar o teor de ferro e zinco e a composição centesimal de farinhas de trigo e milho enriquecidas. Para a avaliação das concentrações de ferro e zinco, aplicou-se a técnica de Espectrometria de Absorção Atômica com Chama. Foram utilizados os métodos oficiais de análise para a determinação de umidade, cinzas, proteínas, carboidratos e lipídeos. Os dados obtidos foram comparados aos valores declarados nos rótulos dos produtos e às especificações recomendadas pela Legislação Brasileira. A concentração de ferro estava acima do especificado para a maioria das amostras. O teor de zinco variou entre 0,6 e 1,5 mg/100 g. Constatou-se que todas as farinhas avaliadas apresentaram características físico-químicas compatíveis com a Legislação. Já em relação ao rótulo dos produtos, verificou-se haver variação entre os valores obtidos e aqueles apresentados na embalagem, para algumas amostras. Os resultados obtidos no trabalho são de grande importância para o alcance dos objetivos da obrigatoriedade do enriquecimento de farinhas.

The aim of this work was to evaluate iron and zinc content and centesimal composition of enriched wheat and corn flours. For iron and zinc evaluation the Flame Atomic Absorption Spectrometry was applied. Official methods of analysis were used for moisture, ash, proteins, carbohydrates and lipids. The obtained data were compared with values in the label of products and the specification recommended by Brazilian Legislation. Iron content was higher than those for most of samples. The amount of zinc varied between 0.6 e 1.5 mg/100 g. The evaluated flours presented physical-chemistry characteristics according to Legislation. However, about products label was the variation between obtained and presented in package values, for some samples, was confirmed. The obtained results are very important to achieve the objectives of the mandatory enrichment of flours.

Development of a methodology for calcium, iron, potassium, magnesium, manganese, and zinc quantification in teas using X-ray spectroscopy and multivariate calibration.

In this study an analytical methodology for food analyses combining X-ray spectroscopy (XRS) with partial least-squares (PLS) data treatment was developed. Fifteen tea samples were purchased at a local market, and XRS spectra were obtained without sample pretreatment. For comparison of the metal concentrations, the samples were also mineralized, and six elements were determined using flame atomic absorption spectrometry (Ca, Fe, Mg, and Mn), flame atomic emission spectrometry (K), and thermospray flame furnace atomic absorption spectrometry (Zn). The spectral information obtained from XRS and the metal concentrations found using the alternative techniques were employed to generate six PLS models. The Ca and Mn models required four latent variables (LV), Fe, five LV, K, two LV, and Mg and Zn, three LV. The limits of quantification for these models were 614, 134, 761, 140, 85, and 1 mg kg(-1) for Ca, Fe, K, Mg, Mn, and Zn, respectively.