RESUMO
In this work, we propose a novel method for yttrium determination by microwave-induced optical emission spectrometry (MIP OES). It is based on the ultrasound-assisted extraction of yttrium with a diluted HNO3 solution and was applied to yttrium determination in phosphorus powder from fluorescent lamps. The method was optimized employing a multivariate strategy, based on a Box-Behnken design, taking into account three experimental factors: mass of the sample (25 to 75 mg), sonication time (15 to 165 min) and HNO3 concentration in the extractant solution (2.0 to 6.0 mol L-1). According to the data obtained in the optimization process, only the sonication time and the HNO3 concentration had an influence on the extraction of yttrium from the samples. The data also indicated that yttrium must be strongly linked to the matrix, since its quantitative extraction was only possible when using the maximum values of the two factors. Therefore, under optimized conditions, we could quantitatively extract yttrium from 75 mg of sample using a 6 mol per L HNO3 solution and a sonication time of 165 min. The limits of detection and quantification for the method were 0.4 and 1.2 µg g-1, respectively, and the intermediary precision (three days) was 14%. The concentration of Y in the analyzed samples varied from 5.37 ± 1.82 to 298 ± 31 µg g-1, and recoveries of 91.0 ± 34.6 and 106 ± 23% were obtained in comparison to total digestion. The results obtained by the proposed method were not statistically different (at the 95% confidence level) from those obtained after the total digestion of the samples when applying the Student's t-test.
RESUMO
In this work, a single-vial methodology for the extraction and cold vapor generation of mercury(II) was developed, followed by the determination of the analyte by atomic absorption spectrometry, with application in water samples of different salinities. L-cystine-modified Fe3O4 nanoparticles (2LcysMNP) were used as sorbent material in the magnetic solid phase extraction (MSPE) in the same flask in which the mercury vapor generation step was performed using a handmade gas-liquid separator developed in our laboratory. The main conditions for extraction, pre-concentration, and cold vapor generation of mercury were optimized. Under the optimized conditions, detection and quantification limits of 0.04 and 0.12 µg L-1, respectively, were achieved with a relative standard deviation of 7.5%. The single-vial system allowed for a preconcentration factor of 30 and an enrichment factor of 24. The accuracy of the method was evaluated by applying it to certified reference materials, and the obtained values were not significantly different from the expected values according to the Student's t-test. Verification of non-specific interferences was assessed by recovery tests, resulting in recoveries ranging from 81 to 111% for water samples of different salinities.
RESUMO
This work reports the development of a flow injection analysis (FIA) system for online magnetic preconcentration and determination of Cd(II) in water by flame atomic absorption spectrometry (F AAS). Magnetic nanoparticles of Fe3O4, functionalized with l-glutamine (GlnMNP), were synthesized and used as a support for Cd(II) retention and preconcentration. Each measurement cycle was performed through online complexation of Cd(II) by l-glutamine attached to Fe3O4 magnetic nanoparticles at pH 10.5, followed by their retention in a coil due to the action of a cylindrical permanent magnet. Subsequently, the retained magnetic nanoparticles containing Cd(II) were dissolved with an acid solution (4 mol L-1 HCl solution), releasing Cd(II) for transportation to the detector. The main chemical and flow parameters that affected the performance of the system were optimized. Under optimum experimental conditions, the limits of detection and quantification were 2 and 5 µg L-1, respectively, and a relative standard deviation of 6.5% (at 50 µg L-1, n = 10) was observed. The FIA system allowed the injection of 24 samples per hour and presented an enrichment factor of four. The method was applied in the analysis of river and pond water samples. The pond water sample was irradiated with ultraviolet light prior to the analysis, in order to eliminate the organic matter. Accuracy of the method was assessed by recovery tests, which provided recovery percentages between 82 and 111%. The developed method was also compared to the direct determination by graphite furnace atomic absorption spectrometry (GF AAS). In this case, the results were not statistical different at 95% confidence level when the Student's t-test was applied.
RESUMO
The synthesis and characterization of the reagent 2-(5-bromothiazolylazo)-4-chlorophenol and its application in the development of a preconcentration procedure for cobalt determination using flame atomic absorption spectrometry after cloud point extraction is presented. This procedure is based on cobalt complexing and entrapment of the metal chelates into micelles of a surfactant-rich phase of Triton X-114. The preconcentration procedure was optimized by using a response surface methodology through the application of the Box-Behnken matrix. Under optimum conditions, the procedure determined the presence of cobalt with an LOD of 2.8 microg/L and LOQ of 9.3 microg/L. The enrichment factor obtained was 25. The precision was evaluated as the RSD, which was 5.5% for 10 microg/L cobalt and 6.9% for 30 microg/L. The accuracy of the procedure was assessed by comparing the results with those found using inductively coupled plasma-optical emission spectrometry. After validation, the procedure was applied to the determination of cobalt in pharmaceutical preparation samples containing cobalamin (vitamin B12).