Juliana Naozuka

Total determination and direct chemical speciation of Hg in fish by solid sampling GF AAS

Simple and rapid analytical procedures for the direct determination of total Hg and for direct chemical speciation of Hg2+ and methylmercury (MHg) in fish were proposed after careful optimization of the heating program and the addition of appropriate chemical modifiers by solid sampling graphite furnace atomic absorption spectrometry (SS-GF AAS). The total determination was done using Ir film and 5 μg Pd + 3 μg Mg solution as permanent and co-injected chemical modifiers, respectively. For direct chemical speciation, 5 μg Pd + 3 μg Mg or 5 μg Pd + 3 μg Mg + 0.5% w/v Triton X-100 solutions were used as co-injected chemical modifiers. The accuracy of both procedures was verified using the certified reference material (CRM) of tuna fish (CE-464), lobster hepatopancreas (TORT-2) and dogfish (DOLT-2). The certified and the found concentrations were statistically concordant (Students t-test). The total Hg concentration in the tuna fish candidate reference material produced in our laboratory was 2.66 ± 0.15 mg kg−1. In the sample ground in a cryogenic mill, the Hg2+ concentrations were 0.553 and 0.559 mg kg−1 and by the difference between the total Hg and Hg2+ concentration was obtained the MHg concentration, 5.11 and 4.73 g kg−1, using Pd + Mg and Pd + Mg + Triton respectively. These results reveal a high concentration of the methylated species that it is most toxic Hg species.

Exploring the emission intensities of ICP OES aided by chemometrics in the geographical discrimination of mineral waters

A rapid method for classification of mineral waters is proposed. The discrimination power was evaluated by a novel combination of chemometric data analysis and qualitative multi-elemental fingerprints of mineral water samples acquired from different regions of the Brazilian territory. The classification of mineral waters was assessed using only the wavelength emission intensities obtained by inductively coupled plasma optical emission spectrometry (ICP OES), monitoring different lines of Al, B, Ba, Ca, Cl, Cu, Co, Cr, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Sb, Si, Sr, Ti, V, and Zn, and Be, Dy, Gd, In, La, Sc and Y as internal standards. Data acquisition was done under robust (RC) and non-robust (NRC) conditions. Also, the combination of signal intensities of two or more emission lines for each element were evaluated instead of the individual lines. The performance of two classification—k-nearest neighbor (kNN) and soft independent modeling of class analogy (SIMCA)—and preprocessing algorithms, autoscaling and Pareto scaling, were evaluated for the ability to differentiate between the various samples in each approach tested (combination of robust or non-robust conditions with use of individual lines or sum of the intensities of emission lines). It was shown that qualitative ICP OES fingerprinting in combination with multivariate analysis is a promising analytical tool that has potential to become a recognized procedure for rapid authenticity and adulteration testing of mineral water samples or other material whose physicochemical properties (or origin) are directly related to mineral content.

Feasibility of Using AAS for the Characterization of a Tuna Fish Candidate Reference Material for Total Hg and Methyl-Hg Measurement

This work describes the evaluation of several parameters for preparing a tuna fish candidate reference material (RM) in order to measure its total Hg and methyl-Hg mass fractions by cold vapor atomic absorption spectrometry (CV-AAS) and solid sampling graphite furnace atomic absorption spectrometry (SS-GF AAS). Best results were acquired after extraction with toluene and L-cysteine for 15 min at 80 °C. The parameters investigated were stability of chemical composition during production, homogeneity and analyte segregation. No analyte segregation was observed and the material was shown to be stable even when stored at 50 °C for 10 months. Total Hg mass fraction was 3.03 ± 0.22 µg g-1 by CV AAS, 2.99 ± 0.43 µg g-1 by SS-GF AAS and 2.95 ± 0.15 µg g-1 by direct mercury analyser (DMA). Methyl-Hg mass fraction was 2.49 ± 0.13 µg g-1 by CV AAS and 2.44 ± 0.46 µg g-1 by SS-GF AAS.

Cooking effects on iron and proteins content of beans (Phaseolus Vulgaris L.) by GF AAS and MALDI-TOF MS

The effects of domestic cooking on proteins, organic compounds and Fe distribution in beans (Phaseolus vulgaris L.) were investigated. Sequential extraction with different extractant solutions (mixture of methanol and chloroform 1:2 v/v, water, 0.5 mol L-1 NaCl, 70% v/v ethanol and 0.5 mol L-1 NaOH) were used for extracting lipids, albumins, globulins, prolamins and glutelins, respectively. Iron determination by graphite furnace atomic absorption spectrometry (GF AAS), proteins by Bradford method and organic compounds by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) were carried out in this work. High concentration of albumins, globulins and glutelins were found in raw beans, while in the cooked beans, albumins and glutelins are main proteins types. The MALDI-TOF MS spectra of raw and cooked beans revealed that the domestic cooking altered the molecular weight of the organic compounds, since that in the cooked beans were found compounds between 2 and 3.5 kDa, which were not presented in the raw beans. Besides this, in cooked beans were also observed the presence of four compounds of high molecular weight (12-16 kDa), being that in the raw grains there is only one (ca. 15.2 kDa). In raw grains is possible to observe that Fe is mainly associated to albumins, globulins and glutelins. For cooked grains, Fe is associated to albumins and globulins.

Chemical Speciation of Iron in Different Varieties of Beans (Phaseolus vulgaris L.): Cooking Effects

Beans are considered a source of iron (Fe), and hence have considerable contribution in cases of Fe deficiency. Beans also contain certain anti-nutritional constituents, which are imperative to the cooking of beans. The nutritional value of beans depends on the bioavailability, which can be affected by cooking. Studies about heating effects in distribution of Fe-based inorganic species are limited, especially for bean cultivars commonly consumed in Brazil. The aim of this work was to evaluate the effects of domestic cooking on the distribution of Fe species (water soluble and inorganic) in seven varieties of Phaseolus beans. Fractionation procedures were used to separate Fe associated to various species. The Fe content was quantified by graphite furnace atomic absorption spectrometry (GF AAS). In raw beans, the inorganic Fe species significantly contributes to the water soluble fraction obtained after fractionation. Cooking lowered the concentration of water soluble Fe in majority varieties of beans.

Effects of Iron Enrichment of Adzuki Bean (Vigna angularis) Sprouts on Elemental Translocation, Concentrations of Proteins, Distribution of Fe-Metalloproteins, and Fe Bioaccessibility

Iron (Fe) is an essential element for human nutrition, and its deficiency or low hemoglobin levels are a global health issue. Strategies aimed at increasing the amounts of essential elementals in agricultural products, as sprouts of adzuki bean (Vigna angularis), can be a way to minimize deficiencies, mainly in the populations of developing countries. Therefore, in this work was evaluated: production of Fe-enriched adzuki bean sprouts; Fe accumulation and translocation in plants in different culture media enriched with different Fe masses (500, 1000, 2000, and 3000 μg); and effects of the enrichment by means of 3000 μg Fe-ethylenediaminetetraacetic acid (Fe-EDTA): on the distribution of Ca, Cu, Fe, K, P, Mg, S, and Zn in different parts of the plant; on protein concentrations (albumins, globulins, prolamins, and glutelins) and their association with Fe in edible parts of the plant (stems); and on Fe bioaccessibility in the edible part of the plant (stems). The enrichment via Fe-EDTA favored the translocation and increased Fe content of sprouts (75%), besides promoting interactions of Fe with albumins (141%), globulins (180%), and glutelins (93%). In the bioaccessibility assays, Fe was 83% bioaccessible in Fe-enriched sprouts.

Protein and Metalloprotein Distribution in Different Varieties of Beans (Phaseolus vulgaris L.): Effects of Cooking

Beans (Phaseolus vulgaris L.) are among the main sources of protein and minerals. The cooking of the grains is imperative, due to reduction of the effect of some toxic and antinutritional substances, as well as increase of protein digestibility. In this study, the effects of cooking on albumins, globulins, prolamins, and glutelins concentration and determination of Fe associated with proteins for different beans varieties and on phaseolin concentration in common and black beans were evaluated. Different extractant solutions (water, NaCl, ethanol, and NaOH) were used for extracting albumins, globulins, prolamins, and glutelins, respectively. For the phaseolin separation NaOH, HCl, and NaCl were used. The total concentration of proteins was determined by Bradford method; Cu and Fe associated with phaseolin and other proteins were obtained by graphite furnace atomic absorption spectrometry and by flame atomic absorption spectrometry, respectively. Cooking promoted a negative effect on (1) the proteins concentrations (17 (glutelin) to 95 (albumin) %) of common beans and (2) phaseolin concentration (90%) for common and black beans. Fe associated with albumin, prolamin, and glutelin was not altered. In Fe and Cu associated with phaseolin there was an increase of 20 and 37% for the common and black varieties, respectively.

Experimento utilizando grãos para explorar a calibração em análises químicas

The conventional curriculum of Analytical Chemistry undergraduate courses emphasizes the introduction of techniques, methods and procedures used for instrumental analysis. All these concepts must be integrated into a sound conceptual framework to allow students to make appropriate decisions. Method calibration is one of the most critical parameters that has to be grasped since most analytical techniques depend on it for quantitative analysis. The conceptual understanding of calibration is not trivial for undergraduate students. External calibration is widely discussed during instrumental analysis courses. However, the understanding of the limitations of external calibration to correct some systematic errors is not directly derived from laboratory examples. The conceptual understanding of other calibration methods (standard addition, matrix matching, and internal standard) is imperative. The aim of this work is to present a simple experiment using grains (beans, corn and chickpeas) to explore different types of calibration methods.