Estudo microestrutural e resistência à corrosão de uma liga de Au soldada a laser, empregada em prótese sobre implantes

Investigou-se o comportamento de juntas soldadas de uma liga a base de ouro utilizada na confecção de próteses odontológicas sobre implantes antes e após ser submetida ao processo de soldagem a laser. Constatou-se que houve uma mudança estrutural na região da solda e esta apresentou uma microestrutura dendrítica refinada e o metal base uma microestrutura granular bifásica com maior dureza e presença de precipitados de Au. Os ensaios eletroquímicos, em meio aerado de NaCl 0,15 molL-1 à temperatura ambiente, que simula as condições do ambiente oral, demonstraram que a junta soldada apresentou melhor desempenho frente à corrosão quando comparada ao metal base; provavelmente devida a estrutura metalúrgica desta região.

Flow injection spectrophotometric determination of adrenaline using a solid-phase reactor containing triiodide ions immobilized in an anion-exchange resin

A flow injection spectrophotometric procedure with on-line solid-phase reactor containing ion triiodide immobilized in an anion-exchange resin is proposed for the determination of adrenaline (epinephrine) in pharmaceutical products. Adrenaline is oxidized by triiodide ion immobilized in an anionic-exchange resin yielding adrenochrome which is transported by the carrier solution and detected at a wavelength of 488 nm. Adrenaline was determined in three pharmaceutical products in the 6.4 x 10-6 to 3.0 x 10-4 mol L-1 concentration range with a detection limit of 4.8 x 10-7 mol L-1. The recovery of this analyte in three samples ranged from 96.0 to 105 %. The analytical frequency was 80 determinations per hour and the RSDs were less than 1 % for adrenaline concentrations of 6.4 x 10-5 and 2.0 x 10-4 mol L-1 (n=10). A paired t-test showed that all results obtained for adrenaline in commercial formulations using the proposed flow injection procedure and a spectrophotometric batch procedure agree at the 95% confidence level.

Direct determination of calcium in milk by atomic absorption spectrometry using flow-injection analysis

A flow-injection system with sample and reagent addition by the synchronous merging zones approach for calcium determination in milk by flame AAS is proposed. Main parameters were optimized using a factorial design with central point. The optimum conditions were 2.5% (m/v) for La concentration, 8 mL min-1 for the carrier flow-rate, 20 cm for coiled reactor and 250 ìL for sample volume. Different sample preparation procedures were evaluated such as dilution in water or acid and microwave-assisted decomposition using concentrated or diluted acids. The optimized flow system was applied to determine Ca in eleven commercial milk samples and two standard reference materials diluted in water. Similar calcium levels were encountered comparing the results obtained by the proposed method (dilution in water) with those obtained using microwave-oven digestion. Results obtained in two standard reference materials were in agreement at 95% confidence level with those certified. Recoveries of spiked samples were in the 93% - 116% range. Relative standard deviation (n = 12) was < 5.4% and the sample throughput was 150 measurements per hour, corresponding to a consumption of 250 µL of sample and 6.25 mg La per determination.

Spectrophotometric flow injection procedure to indirect determination of paracetamol in pharmaceutical formulations using o-tolidine as reagent

A spectrophotometric flow injection method for the determination of paracetamol in pharmaceutical formulations is proposed. The procedure was based on the oxidation of paracetamol by sodium hypochloride and the determination of the excess of this oxidant using o-tolidine dichloride as chromogenic reagent at 430 nm. The analytical curve was linear in the paracetamol concentration range from 8.50 x 10-6 to 2.51 x 10-4 mol L-1 with a detection limit of 5.0 x 10-6 mol L-1. The relative standard deviation was smaller than 1.2% for 1.20 x 10-4 mol L-1 paracetamol solution (n = 10). The results obtained for paracetamol in pharmaceutical formulations using the proposed flow injection method and those obtained using a USP Pharmacopoeia method are in agreement at the 95% confidence level.

Flow injection analysis of vancomycin

A flow injection method for the quantitative analysis of vancomycin hydrochloride, C66H75Cl2N9O24.HCl (HVCM), based on the reaction with copper (II) ions, is presented. HVCM forms a lilac-blue complex with copper ions at pH≅4.5 in aqueous solutions, with maximum absorption at 555 nm. The detection limit was estimated to be about 8.5×10-5 mol L-1; the quantitation limit is about 2.5×10-4 mol L-1 and about 30 determinations can be performed in an hour. The accuracy of the method was tested through recovery procedures in presence of four different excipients, in the proportion 1:1 w/w. The results were compared with those obtained with the batch spectrophotometric and with the HPLC methods. Statistical comparison was done using the Student's procedure. Complete agreement was found at a 0.95 significance level between the proposed flow injection and the batch spectrophotometric methods, which present similar precision (RSD: 2.1 % vs. 1.9%).

Flow injection visible diffuse reflectance quantitative analysis of total sulfur in biodiesel, in plant leaves and in natural waters

Flow injection (FI) methodology, using diffuse reflectance in the visible region of the spectrum, for the analysis of total sulfur in the form of sulfate, precipitated in the form of barium sulfate, is presented. The method was applied to biodiesel, to plant leaves and to natural waters analysis. The analytical signal (S) correlates linearly with sulfate concentration (C) between 20 and 120 ppm, through the equation S=-1.138+0.0934 C (r = 0.9993). The experimentally observed limit of detection is about 10 ppm. The mean R.S.D. is about 3.0 %. Real samples containing sulfate were analyzed and the results obtained by the FI and by the reference batch turbidimetric method using the statistical Student's t-test and F-test were compared.