Vinicius Câmara Costa

Multivariate optimization of simple procedure for determination of Fe and Mg in cassava starch employing slurry sampling and FAAS

A slurry sampling procedure has been developed for Fe and Mg determination in cassava starch using flame atomic absorption spectrometry. The optimization step was performed using a univariate methodology for 200mg samples and a multivariate methodology, using the Box-Behnken design, for other variables, such as solvent (HNO3:HCl), final concentration (1.7molL-1) and time (26min). This procedure allowed determination of iron and magnesium with detection limits of 1.01 and 3.36mgkg-1, respectively. Precision, expressed as relative standard deviation (%RSD), was of 5.8 and 4.1% (n=10) for Fe (17.8mgkg-1) and Mg (64.5mgkg-1), respectively. Accuracy was confirmed by analysis of a standard reference material for wheat flour (NIST 1567a), which had certified concentrations of 14.1±0.5mgkg-1 for Fe and 40±2.0mgkg-1 for Mg, and the concentrations found using proposed method were 13.7±0.3mgkg-1 for Fe and 40.8±1.5mgkg-1 for Mg. Comparison with concentrations obtained using closed vessel microwave digestion was also realized. The concentrations obtained varied between 7.85 and 17.8mgkg-1 for Fe and 23.7-64.5mgkg-1, for Mg. The simplicity, easily, speed and satisfactory analytical characteristics indicate that the proposed analytical procedure is a good alternative for the determination of Fe and Mg in cassava starch samples.

Use of laser-induced breakdown spectroscopy for the determination of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) concentrations in PC/ABS plastics from e-waste

Due to the continual increase in waste generated from electronic devices, the management of plastics, which represents between 10 and 30% by weight of waste electrical and electronic equipment (WEEE or e-waste), becomes indispensable in terms of environmental and economic impacts. Considering the importance of acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), and their blends in the electronics and other industries, this study presents a new application of laser-induced breakdown spectroscopy (LIBS) for the fast and direct determination of PC and ABS concentrations in blends of these plastics obtained from samples of e-waste. From the LIBS spectra acquired for the PC/ABS blend, multivariate calibration models were built using partial least squares (PLS) regression. In general, it was possible to infer that the relative errors between the theoretical or reference and predicted values for the spiked samples were lower than 10%.

Direct determination of Ca, K, Mg, Na, P, S, Fe and Zn in bivalve mollusks by wavelength dispersive X-ray fluorescence (WDXRF) and laser-induced breakdown spectroscopy (LIBS)

This study aims to develop methods for determination of Ca, K, Mg and Na by laser-induced breakdown spectroscopy (LIBS) and Ca, K, Mg, Na, P, S, Fe and Zn by wavelength dispersive X-ray fluorescence (WDXRF) in pressed pellets bivalve mollusks. LIBS and WDXRF calibration models were built with references values determined by inductively coupled plasma optical emission spectrometry (ICP OES) after acid digestion. The calibration models for LIBS and WDXRF were obtained from 28 samples (14 for calibration and 14 for validation). It was possible to implement a validation between LIBS and WDXRF methods for elements Ca, K, Mg and Na. The proposed calibration model obtained using LIBS and WDXRF data presented a good correlation with reference values obtained by ICP OES.

Application of Factorial Design and Desirability Function to Develop a Single Analytical Procedure for the Determination of Metals in Different Tissues of Blue Crab (Callinectes danae)

In this scientific work, it was developed a single analytical procedure for the sample preparation of different tissues of blue crabs using microwave-assisted digestion for the determination of Cu, Mn, Fe and Zn by fast sequential flame atomic absorption spectrometry (FS FAAS). The limits of quatification were 10.5, 1.6, 8.9 and 19.3 μg g for Cu, Mn, Fe and Zn, respectively. The precision was estimated in terms of repeatability using the relative standard deviation (RSD, n = 7) 3.4% for Cu; 4.8% (Mn); 4.7% (Fe) and 4.7% (Zn) and accuracy of the procedure was confirmed by analysis of certified reference material (CRM) of oyster tissue (NIST 1566B) with concentration values of 71.3 for Cu, 18.3 for Mn, 202.5 for Fe and 1415 μg g for Zn. The procedure has been applied for the determination of Cu, Mn, Fe and Zn in several blue crab samples from Cachoeira River estuary, Ilhéus, Bahia, Brazil.

Multi-energy calibration (MEC) applied to laser-induced breakdown spectroscopy (LIBS)

In this study, the multi-energy calibration (MEC) method is applied to solid sample analysis by laser-induced breakdown spectroscopy (LIBS). The MEC method uses only two calibration standards and several atomic emission wavelengths with different sensitivities to determine the analyte concentration in the sample. Both calibration mixtures are prepared using the same amount of sample, which contributes to minimizing matrix effects. The MEC-LIBS method was used to determine Ca, Cu, Fe, Mn and Zn in complex-matrix samples of cattle mineral supplements with an adequate sample throughput (15 samples per h). The limits of detection (LODs) calculated for these elements in the solid sample were 11 g kg−1, 45, 188, 53 and 44 mg kg−1, respectively. For Cu, Mn and Zn, these LODs were approximately 10, 10, and 20 times lower than the minimum level required in a commercial product by the Brazilian legislation. The methods accuracy was evaluated by analyzing five reference materials (RM) of cattle mineral supplements, and by comparing values determined in six commercial samples with results from ICP-OES determinations. No statistically significant difference was observed between MEC-LIBS and RM or ICP-OES-determined values at the 95% confidence level (Student’s t-test, n = 3). LIBS is an inherently atomic-emission-rich technique, which suffers from severe matrix effects. MEC is an efficient matrix-matching method, for which the larger the number of analytical signal sources for an analyte the more precise the results. Therefore, MEC is a highly compatible, complementary approach to LIBS calibration.

Use of Mixture Design with Minimal Restrictions to Optimize an Extraction Procedure Employing Diluted Acids Assisted by Ultrasound and Microwave for Nutrient Element Determination in Vegetal Samples

In this work, it was developed an alternative analytical strategy for the preparation of vegetal samples extracted with diluted acids and assisted by ultrasound and microwave radiation for the determination of nutrients elements by fast sequential flame atomic absorption spectrometer. The conditions optimized using univariate and multivariate methodologies for the procedure were as follows: 200 mg of sample; extraction solution comprising a mixture of 6.3 mL HNO3, 2.1 mL HCl, and 1.7 mL CH3COOH; extractor with a final concentration of 2.5 mol L; a sonication time of 30 min; and a microwave radiation time of 6 s. The accuracy of the procedure was confirmed by analyzing the certified reference material NIST 1515 (apple leaves) and by comparison with the results obtained through microwave-assisted total digestion method. The procedure was applied to determine Ca, Mg, Cu, Mn, Fe, and Zn in several cassava peel samples used in animal nutrition, and proved to be simple, reliable, fast, easy to implement, and inexpensive.

Aplicação do Extrato De Amêndoa de Cacau ( Theobroma Cacao. L ) como um Novo Indicador em Titulações Ácido-Base

Neste trabalho, foi proposto a utilizacao de um indicador natural obtido das sementes do Theobroma cacao L. (cacau) que e uma planta encontrada em abundância no sul da Bahia, Brasil. O extrato que contem os corantes a partir de sementes de cacau foi aplicado como indicador em titulacoes acido / base, e os resultados foram comparados com os valores obtidos na titulacao potenciometrica e utilizando a fenolftaleina como um indicador de referencia. As metodologias que envolvem acidos fracos e fortes foram aplicadas com os alunos de pos-graduacao de Quimica da Universidade Estadual de Santa Cruz, em Ilheus, Bahia, Brasil. DOI: 10.5935/1984-6835.20150081