No abstract

In this work the performance of some chemical modifiers (no modifier, Pd 1 Mg, Ir in solution, Ru, Ir or Zr independently as permanent modifier and Ir 1 Rh permanent) was investigated for the direct determination of Bi in human urine by electrothermal atomic absorption spectrometry (ETAAS). The urine samples were diluted directly in the autosampler cups with one-fold dilution with nitric acid 1% v/v. The obtaining of the permanent modifiers (500 mg of iridium, ruthenium and zirconium independently and 250 mg of Ir plus 250 mg of rhodium) was described elsewhere. Without modifier at all temperatures the signal was negative with a high background. Using Pd 1 Mg the best temperatures were of 1000 and 2500 uC, respectively, for pyrolysis and atomization, but the sensitivity was half that when using Ir 1 Rh. Using ruthenium, iridium or zirconium independently no peak was obtained but a plateau that did not return to baseline even in 15 s of atomization. With iridium applied in solution together with the sample the best pyrolysis and atomization temperatures were of 900 and 2500 uC, respectively, but the sensitivity was analogous with that obtained using Pd 1 Mg. Using Ir 1 Rh, the optimum pyrolysis and atomization temperatures were lower (900 and 1400 uC), but in this case the best sensitivity was obtained with a characteristic mass of 29.2 pg (recommended of 30 pg for the manufacturer for the metal in aqueous solutions). With this modifier, the obtained peak was very symmetrical, returning to the baseline in 3 s with very low background. The use of low temperatures and a low time of atomization coupled to the use of permanent modifer will certainly extend the lifetime of the graphite tube. Aqueous calibration curves and standard addition were parallel with slopes of 0.042 and 0.044 for aqueous and standard addition, respectively. For this reason, the calibration was carried out with aqueous solutions. The r values of calibration curves were higher than 0.99. Spiked urine samples with 5.0, 10.0, 15.0, 20.0, 25.0 and 30.0 mg l 21 , analysed on different days, presented a recovery between 80.0 and 100.0%. The limit of detection was 50 pg. The lifetime of the tube was more than 500 cycles of atomization.

O objeto do presente estudo foi o desenvolvimento de metodologias alternativas para determinação direta de chumbo em amostras não digeridas de urina humana e soro, por espectrometria de absorção atômica com atomização eletrotérmica. Neste sentido algumas substâncias foram investigadas para atuarem como modificador químico. Volumes de 20 μL de amostras de urina diluídas 1 + 1, v/v e de soro 1 + 4, v/v, com HNO 3 1% v/v e 0,02% v/v de cloreto de trimetilcetil amônio (CTAC) foram preparados diretamente nos copos do amostrador automático e introduzidos no forno de grafite. Para modificadores em solução foram usados 10 μL. Curvas de temperaturas de pirólise e atomização foram usadas em todas otimizações nas matrizes diluídas. Para urina, com o uso de irídio permanente (500 μg), as melhores temperaturas de pirólise e atomização foram de 900 e 1600 o C respectivamente, com uma massa característica de 12 pg (recomendada de 10 pg), com pulsos de absorção simétricos e fundo corrigido. Amostras de urina contaminadas apresentaram recuperações entre 86 e 112%, usando Ir permanente. Analisando amostras de urina certificada, os resultados encontrados foram concordantes com os valores certificados (considerando um intervalo de confiança de 95%) para dois níveis do metal. Para soro, bons resultados foram obtidos com a mistura de Zr + Rh ou Ir + Rh como modificadores permanentes, com massas características de 9,8 e 8,1 pg respectivamente. Recuperações de amostras de soro contaminadas variaram entre 98,6 e 100,1% (Ir + Rh) e entre 93,9 e 105,2% (Zr + Rh). Em ambos os estudos de recuperação, o desvio padrão relativo (n=3) foi menor que 7%. A calibração para ambas as amostras foi feita através de curvas de calibração aquosas que apresentaram r 2 maior que 0,99. Os limites de detecção foram de 0,7 μg L -1 para as amostras de soro, usando Zr + Rh permanente, e de 1,0 μg L -1 para urina com irídio permanente.The object of the present study was the development of alternative methods for the direct determination of lead in undigested samples of human urine and serum by electrothermal atomic absorption spectrometry (ET AAS). Thus, some substances have been investigated to act as chemical modifiers. Volumes of 20 μL of diluted samples, 1 + 1, v/v for urine and 1 + 4, v/v for serum, with HNO 3 1% v/v and 0.02% v/v of cetil trimethyl ammonium chloride (CTAC) were prepared directly in the autosampler cups and placed into the graphite furnace. For modifiers in solutions 10 μL were used. Pyrolysis and atomization temperature curves were used in all optimizations in the matrixes diluted as exposed. For urine with permanent iridium (500 μg), the best pyrolysis and atomization temperatures were 900 and 1600 ºC, respectively, with a characteristic mass of 12 pg (recommended of 10 pg), with symmetrical absorption pulses and corrected background. Spiked urine samples presented recoveries between 86 and 112% for Ir permanent. The analysis results of certified urine samples are in agreement with certified values (95% of confidence) for two levels of th...

Different chemical modifiers for use with electrothermal atomic absorption spectrometry (ET AAS) were investigated in relation to determining the selenium in human urine samples. The samples were diluted in a solution containing 1% v/v HNO3 and 0.02% m/v cetyltrimethylammonium chloride (CTAC). Studying the modifiers showed that the use of either Ru or Ir as the permanent modifier gave low sensitivity to Se and the peak shape was very noisy, while Zr or Rh gave no peak at all. The same occurred when Zr was used in solution. For mixtures of permanent modifiers, Ir plus Rh or Zr plus Rh gave very low sensitivity, Zr plus Rh with co-injection of Ir in solution was also not efficient, Zr plus Rh in solution gave good sensitivity, but the best results were obtained with a mixture of Zr and Rh as the permanent modifier and co-injection of Rh in solution. Using this last modifier, the following dilutions with the HNO3 and CTAC were studied: 1:1, 1:2, 1:3 and 1:4. The best dilution was 1:1, which promoted good sensitivity and a more defined peak shape and made it possible to correct for the background using a deuterium arc lamp. Under these conditions, a characteristic mass of 26+/-0.2 pg was obtained for Se in aqueous solution. Six certified urine samples were analyzed using matrix matching calibration and the measured concentrations were in agreement with the certified values, according to a t-test at the 95% confidence level. Recovery tests were carried out and the recoveries were in the range 100-103%, with relative standard deviation better than 9%. The limit of detection (LOD, 3 sd, n = 10) was 3.0 microg L(-1) in the sample. The treated graphite tube could be used for at least 600 atomization cycles without significant alteration of the analytical signal.