Anderson Schwingel Ribeiro

Determination of inorganic and total mercury in biological samples treated with tetramethylammonium hydroxide by cold vapor atomic absorption spectrometry using different temperatures in the quartz cell

A very simple procedure is proposed for the determination of total and inorganic Hg in biological materials. Organic Hg (methylmercury) can be obtained from the difference. After treating the sample at room temperature with tetramethylammonium hydroxide (TMAH), inorganic Hg is obtained by cold vapor atomic absorption spectrometry (CV-AAS), keeping the quartz cell at room temperature, while total Hg is obtained by the same technique, heating the quartz cell in an air–acetylene flame. By analyzing several biological certified materials, it was evident that the difference between the mentioned concentrations corresponds to methylmercury. Cold vapor graphite furnace atomic absorption spectrometry (CV-GF-AAS) with retention of the vapor in a heated Au-treated graphite tube was used to optimize the vapor generation conditions and also to determine total Hg. In a general way, the concentrations obtained by both techniques were in agreement with the certified values or with differences of the certified values for total, Hg2+ and CH3Hg+, according to the t-test for a 95% confidence level. Total Hg results obtained by the two techniques were also in agreement. The relative standard deviations were lower than 10% for most of the results. The detection limits in the sample were: 0.13 μg g−1 for total Hg and 0.025 μg g−1 for Hg2+ by CV-AAS. The detection limit for total Hg by CV-GF-AAS was 0.001 μg g−1. It is amazing how this very simple method is able to provide very important information on mercury speciation.

Determination of Cd in biological samples by flame AAS following on-line preconcentration by complexation with O,O-diethyldithiophosphate and solid phase extraction with Amberlite XAD-4.

A method for the on-line preconcentration of Cd based on its complex formation with the ammonium salt of O,O-diethylditiophosphate (DDTP) and using the Amberlite XAD-4 resin as a solid support in a column is proposed. Cadmium was detected by flame atomic absorption spectrometry. Different conditions, such as complexing agent concentration, preconcentration time, solutions flow rates and nature and concentration of the eluent were optimized. Different detection limits (LODs) could be established by using different preconcentration times, between 30s and 5min, with corresponding LODs from 5 to 1mugL(-1), respectively. The method was validated by analyzing five biological certified samples. The relative standard deviation was usually around 3%, indicating a very good precision. The found concentrations values are in agreement with the certified ones, according to the t-test, for a confidence level of 95%. Enriched seawaters were also analyzed, and the recoveries were between 93 and 108%. The FI method is very simple and probably can be coupled to other measuring analytical techniques.

Determination of As, Cd, Ni and Pb in human hair by electrothermal atomic absorption spectrometry after sample treatment with tetramethylammonium hydroxide

Abstract A very simple alternative dissolution procedure for a human hair sample with tetramethylammonium hydroxide was proposed. The sample was mixed with a small amount of the reagent and the dissolution occurred in approximately 2 h at room temperature or in approximately 10 min under heating at 60–70°C. After dissolution, the analytes, As, Cd, Ni and Pb were determined in a certified reference human hair by electrothermal atomic absorption spectrometry, using calibration curves obtained by separately pipetting the analyte, the modifier and the reagent solutions into the graphite tube. A mixture of Pd and phosphate for Pb and Pd alone for As and Cd were used as modifiers, while no modifier was employed for Ni. The temperature program was optimized through pyrolysis and atomization curves. The limits of detection in the sample were 0.4, 0.009, 0.1 and 0.5 ppm, respectively, for As, Cd, Ni and Pb. The relative standard deviations were lower than 5%. The obtained concentrations agreed with the certified values and also with the found concentrations by using a conventional acid dissolution.

Slurry sampling for Hg determination in sediments, sewage sludge and coal samples by cold vapor atomic absorption spectrometry

Um metodo simples e robusto para a determinacao de Hg em amostras ambientais por espectrometria de absorcao atomica com geracao de vapor frio diretamente de suspensoes acidas e proposto. Apos reducao do tamanho das particulas da amostra para < 50 µm em gral de agata, dois procedimentos foram utilizados para a preparacao das suspensoes: com 6,7% v/v de acido nitrico ou 10% v/v de agua-regia mais 2% v/v de acido fluoridrico. Dependendo da amostra, a concentracao da amostra na suspensao variou de 3,3 a 23 mg mL-1. O vapor frio de Hg gerado diretamente das suspensoes acidas das amostras foi conduzido para o tubo T de quartzo, posicionado no lugar do atomizador do espectrometro. Oito amostras ambientais de referencia certificadas foram analisadas. Pelo uso da calibracao convencional com padroes aquosos, excelentes resultados foram obtidos quando a agua-regia mais o acido fluoridrico foram utilizados nas suspensoes. Amostras de sedimento e carvao de Santa Catarina, Brasil, tambem foram analisadas. O limite de deteccao foi de 30 ng g-1. Simplicidade, baixo custo e alta eficiencia sao algumas qualidades do metodo proposto, mostrando-se adequado para analises de rotina.

Simultaneous on-line pre-concentration and determination of trace metals in environmental samples by flow injection combined with inductively coupled plasma mass spectrometry using silica gel modified with niobium(V) oxide

This work presents the development of an on-line pre-concentration system for simultaneous determination of Cd, Cu, Ni, V, Zn, Co and Pb in aqueous environmental samples and detection by inductively coupled plasma mass spectrometry. The system is based on cationic retention of the analytes onto a mini-column filled with silica gel modified with niobium(V) oxide. The effects of chemicals and flow variables have been investigated. The optimized operating conditions, selected as a compromise between sensitivity and analytical frequency were: sample pH 7.0, sample flow rate of 6.0mL min(-1), eluent flow rate of 2.0mL min(-1), and eluent (HNO(3)) concentration of 2.5mol L(-1). The relative standard deviation (n=7), enrichment factor and linear working range were 0.8-4.5%, 23.3-37.2 and 0.05-25.0microg L(-1), respectively. Limits of detection were between 0.01 and 0.03microg L(-1). The accuracy of the proposed method was checked with certified materials (NASS-4, NASS-5, CASS-4 and SRM 1643e). Values obtained were in accordance with those reported for the certified materials. Recovery was found to be in the range of 90-110% for a suit of water samples with variable matrices (seawater, tap water and ground water) collected in Florianopolis, Brazil.

Determination of Hg and Se in biological materials by chemical vapor generation electrothermal vaporization inductively coupled plasma mass spectrometry using isotope dilution calibration after microwave-assisted digestion with Aqua Regia

Propoe-se um metodo para a determinacao de Hg e Se em materiais biologicos por espectrometria de massa com plasma indutivamente acoplado e introducao da amostra por vaporizacao eletrotermica apos geracao quimica de vapor (CVG-ETV-ICP-MS) e calibracao por diluicao isotopica. As amostras foram digeridas com agua regia em um sistema convencional de microondas. As razoes isotopicas usadas para quantificacao foram: 201Hg/202Hg e 77Se/82Se. Borohidreto de sodio foi usado como agente redutor. As temperaturas de retencao e vaporizacao foram de 150 e 2000 °C, respectivamente. Seis materiais biologicos certificados foram analisados e as concentracoes obtidas para Hg e Se foram concordantes com os valores certificados de acordo com o teste-t para um nivel de confianca de 95%. Os limites de deteccao obtidos foram 0,7 e 3 ng g-1 para Hg e Se, respectivamente. O metodo e preciso, exato e adequado para a analise de materiais biologicos em rotina e demonstra a viabilidade do uso da diluicao isotopica no sistema proposto.

Evaluation of pH and Calcium Ion Release of a Dual-cure Bisphenol A Ethoxylate Dimethacrylate/Mineral Trioxide Aggregate–based Root-end Filling Material

INTRODUCTION The incorporation of light-curable resins has been proposed for mineral trioxide aggregate (MTA) to improve its properties and reduce its setting time. The aim of the present study was to assess the pH and calcium ion release of an experimental bisphenol A ethoxylate dimethacrylate/MTA-based root-end filling material (E-MTA) in comparison with white MTA Angelus (Angelus, Londrina, PR, Brazil) (W-MTA) and to evaluate the influence of the addition of calcium chloride (CaCl2) on these properties. METHODS Polyethylene tubes filled with the materials were immersed in deionized water for the measurement of pH (digital pH meter) and calcium release (atomic absorption spectrophotometry). The evaluations were performed at 3 and 24 hours and 7, 15, and 30 days. Data were measured using 2-way repeated measures of variance followed by the Holm-Sidak method (P < .05). RESULTS All materials presented a reduction in the pH and released calcium ions during the 30 days of the study. E-MTA showed a significantly lower calcium ion release capacity when compared with W-MTA (P < .05). The calcium release of E-MTA + 5% CaCl2 was similar to W-MTA (P > .05). CONCLUSIONS The monomer bisphenol A ethoxylate dimethacrylate added to MTA formed a material with a lower capacity of calcium release than W-MTA despite maintaining a similar pH. However, the addition of CaCl2 improved the calcium release of this material.

Avaliação da Concentração de Mercúrio em Amostras de Biodiesel por Geração Fotoquímica de Vapor

In this paper, the photochemical vapor generation coupled with atomic absorption spectrometry was used to assess the concentration of Hg in biodiesel samples. The main parameters to assess the best conditions for the photochemical vapor generation of Hg were investigated (sample mass, formic acid concentration, irradiation time and gas flow rate). Volatile species of Hg were generated in biodiesel samples prepared in 20% (v/v) formic acid and 76% (v/v) ethanol. Analytical curves were generated using inorganic (Hg 2+ ) and organic standards (CH3Hg + e C2H5Hg + ) in ethanol and showed correlation coefficients higher than 0.99. The limits of detection and quantification, in μg L -1 , were 0.01 and 0.05, respectively. Due to the lack of biodiesel samples with a certified concentration of Hg, the accuracy was evaluated by assessing the recoveries of species of Hg added to the samples, obtaining values ranged from 101.0 to 111.9% of recoveries. The relative standard deviation values were lower than 0.1%, indicating an excellent precision of the method. No Hg was detected in the biodiesel samples, considering the obtained limit of detection. The proposed method is sensitive and the sample pre-treatment is simple and practical.

Assessment of selenium bioaccumulation in lactic acid bacteria

Selenium is an essential micronutrient for living beings, as it helps to maintain the normal physiological functions of the organism. The numerous discoveries involving the importance of this element to the health of human beings have fostered interest in research to develop enriched and functional foods. The present study evaluated the potential for bacterial strains of Enterococcus faecalis (CH121 and CH124), Lactobacillus parabuchneri (ML4), Lactobacillus paracasei (ML13, ML33, CH135, and CH139), and Lactobacillus plantarum (CH131) to bioaccumulate Se in their biomass by adding different concentrations of sodium selenite (30 to 200 mg/L) to the culture medium. Quantification of Se with UV and visible molecular absorption spectroscopy showed that the investigated bacteria were able to bioaccumulate this micromineral into their biomass. Two of the L. paracasei strains (ML13 and CH135) bioaccumulated the highest Se concentrations (38.1 ± 1.7 mg/g and 40.7 ± 1.1 mg/g, respectively) after culture in the presence of 150 mg/L of Se. This bioaccumulation potential has applications in the development of dairy products and may be an alternative Se source in the diets of humans and other animals.