ONLINE OXIDATION OF CR(III) TO CR(VI) FOR USE WITH THE FLOW-INJECTION ANALYSIS TECHNIQUE

109564564

Selective Spectrophotometric Determination Of Trace Amounts Of Chromium(vi) Using A Flow Injection System With A Microcolumn Of Zirconium(iv) Oxide Modified Silica Gel

Zirconium(IV) oxide coated on a silica gel surface was found to be very effective for extracting CrVI from aqueous solutions at a pH of about 3. A microcolumn packed with this material was inserted into a flow injection system for the separation and preconcentration of CrVI. By this process, a concentration level of 2 ppb was detected with a relative standard deviation of 2.4%. Because of the high selectivity of the immobilized substrate, it was possible to determine CrVI in the presence of larger amounts of other ions. The analysis was also carried out on natural water spiked with CrVI, and compared with a standard method.11761029103

Determination of selenium in some food matrices by electrothermal atomic absorption spectrometry after preconcentration with diethyldithiophosphate

Selenium preconcentration for its electrothermal atomic absorption spectrometric determination in biological tissues, such as food samples, is described. The method is applicable to matrices containing 0.05-1 mg kg(-1) Se, like fish, meat, and flour. After a closed nitric acid digestion procedure, an aliquot of the sample is diluted with 0.2% v/v HNO3, diethyldithiophosphate solution is added and the complex formed is loaded on a minicolumn containing 30 mg of SiO2-C-18, using a peristaltic pump. The complex, eluted with ethanol, is collected into a cuvette for the determination of selenium. A calibration curve is made from selenium(IV) solutions, prepared in 0.2% v/v HNO3. In order to minimize diethyldithiophosphate interference, a chemical modifier is used, chosen after comparison among Rh, Pd, Ir and Ni, and Rh proved to be the best. The furnace program can include a pyrolysis step at 1000degreesC or, alternatively, omit it, skipping from a drying step to the atomization. A typical analytical curve goes up to 4 ng mL(-1) Se. An enrichment factor of 65 is possible, taking 6 min for each preconcentration step. Good results were obtained for several certified reference materials. The entire procedure, including the digestion, can proceed rapidly, because there is no need for a pre-reduction step, coprecipitation or a lengthy solvent extraction.18778378

On-line Oxidation Of Cr(lll) To Cr(vi) For Use With The Flow Injection Analysis Technique

An on-line procedure for the oxidation of Cr(III) to Cr(VI) was developed. The extent of oxidation was followed using the 1,5-diphenylcarbazide (DPC) spectrophotometric method accommodated in a flow injection analysis (FIA) system. Cerium(IV) sulphate and potassium peroxydisulphate were tested as oxidising agents. Despite the high oxidation power of the peroxydisulphate ion in acidic solution, the use of Ce(IV) is more convenient under dynamic conditions. The best experimental conditions were obtained at 45°C using a 0.025% m/\/Ce(IV) solution in 0.07 M H2SO4 with the Cr(III) solutions containing up to 3.0 × 10-2 M H 2S04.109564564

SPECTROPHOTOMETRIC DETERMINATION OF BORON IN PLANTS USING MONOSEGMENTED CONTINUOUS-FLOW ANALYSIS

113228929

Spectrophotometric Determination Of Boron In Plants Using Monosegmented Continuous Flow Analysis

A monosegmented continuous flow analysis (MCFA) procedure for the spectrophotometric determination of boron using azomethine-H as colour reagent is presented. Under the experimental conditions described the calibration graph is linear up to 4.00 μg ml-1. The detection limit found is 0.02 μg ml-1, calculated from three times the standard deviation of the blank signal. The common interfering elements present in plants were investigated under dynamic MCFA conditions. As expected, iron and copper present the most severe interferences. This MCFA method for the determination of boron was used with test samples from the Plant Sample Exchange Programme (PSEP) of the Wageningen Agricultural University. The results compared favourably with those obtained by the conventional static procedure and those published by the PSEP.113289293CNRS/IN2P3; NSF; Arthritis National Research Foundation; NRF-2012004024; ANRF; Arthritis National Research Foundatio

Classification of processed and natural coconut water using HCA, PCA and metallic ion levels obtained by Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES).

Inductively Coupled Plasma Optical Emission Spectrometry was used to determine Ca, Mg, Mn, Fe, Zn and Cu in samples of processed and natural coconut water. The sample preparation consisted in a filtration step followed by a dilution. The analysis was made employing optimized instrumental parameters and the results were evaluated using methods of Pattern Recognition. The data showed common concentration values for the analytes present in processed and natural samples. Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) indicated that the samples of different kinds were statistically different when the concentrations of all the analytes were considered simultaneously.29465465

TaC formation on graphite surface. Part I: Immersion in aqueous solution of TaF7(2-)

The atomic absorption spectrometry with electrothermal atomization in graphite oven, as an analytical method, possesses a great advantage of high sensibility detection; due to this advantage, it has been largely accepted as an analytical routine in application and research laboratories. In spite of its large detection power, the application of this methodology is limited by the operation cost and by the chemical interaction of some elements with the graphite tube surface. This work presents the methodologies of formation of tantalum carbide in the surface of graphite tubes by immersion of the graphite tube in aqueous solution of TaF7(2-). The samples obtained following this methodology were thermally treated in order to obtain the tantalum carbide. The homogeneity of the formed layers and their morphologies were characterized by scanning electron microscopy; the formation of tantalum carbide was confirmed by X-ray diffraction.A espectrometria de absorção atômica com atomização eletrotérmica em forno de grafite, como método analítico, possui uma grande vantagem que é a sensibilidade na detecção, tendo assim grande aceitação como rotina analítica em laboratórios de aplicação e pesquisa. Apesar desta metodologia possuir grande poder de detecção, sua aplicação é limitada pelo custo de operação e pela interação química de alguns elementos com a superfície do tubo de grafite. Este trabalho apresenta uma metodologia para obtenção de uma camada de carbeto de tântalo na superfície do grafite, cujas propriedades permitem a atomização do analito sem interferência da camada formada. A metodologia apresentada neste trabalho é a imersão do tubo de grafite em solução aquosa de TaF7(2-). Os corpos de prova obtidos foram submetidos a tratamentos térmicos para a formação do carbeto de tântalo. A homogeneidade das camadas formadas e suas morfologias foram acompanhadas por microscopia eletrônica de varredura e a formação do carbeto de tântalo foi confirmada por difratometria de raios X.14414

A Multifaceted Analysis of Immune-Endocrine-Metabolic Alterations in Patients with Pulmonary Tuberculosis

Our study investigated the circulating levels of factors involved in immune-inflammatory-endocrine-metabolic responses in patients with tuberculosis with the aim of uncovering a relation between certain immune and hormonal patterns, their clinical status and in vitro immune response. The concentration of leptin, adiponectin, IL-6, IL-1β, ghrelin, C-reactive protein (CRP), cortisol and dehydroepiandrosterone (DHEA), and the in vitro immune response (lymphoproliferation and IFN-γ production) was evaluated in 53 patients with active untreated tuberculosis, 27 household contacts and 25 healthy controls, without significant age- or sex-related differences. Patients had a lower body mass index (BMI), reduced levels of leptin and DHEA, and increased concentrations of CRP, IL-6, cortisol, IL-1β and nearly significant adiponectin values than household contacts and controls. Within tuberculosis patients the BMI and leptin levels were positively correlated and decreased with increasing disease severity, whereas higher concentrations of IL-6, CRP, IL-1β, cortisol, and ghrelin were seen in cases with moderate to severe tuberculosis. Household contacts had lower DHEA and higher IL-6 levels than controls. Group classification by means of discriminant analysis and the k-nearest neighbor method showed that tuberculosis patients were clearly different from the other groups, having higher levels of CRP and lower DHEA concentration and BMI. Furthermore, plasma leptin levels were positively associated with the basal in vitro IFN-γ production and the ConA-driven proliferation of cells from tuberculosis patients. Present alterations in the communication between the neuro-endocrine and immune systems in tuberculosis may contribute to disease worsening