Iracema Takase

Chemical vapor generation—electrothermal atomic absorption spectrometry: new perspectives☆

Abstract Volatile species of Ag, Cu, Cd, and Zn were generated at room temperature by the addition of sodium tetrahydroborate (III) to an acidified solution of the analytes. The vapor-phase species were rapidly transported to a pre-heated graphite tube, the surface of which was previously treated with Ir as a permanent chemical modifier. The volatile species were trapped at the Ir treated tube surface, and the further heating of the furnace permits their determination by atomic absorption spectrometry. A univariate approach was used to achieve optimized conditions and derive the figures of merit. The limits of detection based on a 3σ b criterion were 10 (1); 0.006 (6×10 −4 ); 28 (2.8) and 1.1 (0.11) ng (μg ml −1 ) for Ag, Cd, Cu and Zn, respectively. Precision of replicate measurements was typically approximately 10% R.S.D. Using a transfer line as short as possible should minimize losses of analyte during the transport to the graphite furnace. The overall efficiency of the volatile species generation and trapping process estimated for silver was 13%.

A geração química de vapor em espectrometria atômica

The historical development of atomic spectrometry techniques based on chemical vapor generation by both batch and flow injection sampling formats is presented. Detection via atomic absorption spectrometry (AAS), microwave induced plasma optical emission spectrometry (MIP-OES), inductively coupled plasma optical emission spectrometry (ICP-OES) , inductively coupled plasma mass spectrometry (ICP-MS) and furnace atomic nonthermal excitation spectrometry (FANES) are considered. Hydride generation is separately considered in contrast to other methods of generation of volatile derivatives. Hg ¾ CVAAS (cold vapor atomic absorption spectrometry) is not considered here. The current state-of-the-art, including extension, advantages and limitations of this approach is discussed.

Minimization of Cu and Ni interferences in the determination of Sb by hydride generation atomic absorption spectrometry: the use of picolinic acid as masking agent and the influence of l-cysteine

Abstract The minimization of copper and nickel interference on the determination of antimony by hydride generation atomic absorption spectrometry using picolinic acid and l -cysteine as masking agents was studied. Concentrations up to 4000 and 1000 mg l −1 of nickel and copper respectively were found to be tolerable in the presence of picolinic acid. The simultaneous presence of both transition metals could be tolerated by using a mixture of picolinic acid and l -cysteine. In the analysis of a nickel oxide certified reference material good agreement between the recommended and found values was verified. A detection limit (3 s, n =10) of 0.1 μg Sb g −1 in the original sample was estimated.

Adsorptive preconcentration for voltammetric measurements of trace levels of vanadium in the presence of copper

Abstract An electrochemical stripping procedure for trace measurements of vanadium is described in which preconcentration is achieved by the adsorption of a vanadium-2-(2′-thiazolylaloz)- p -cresol complex on a static mercury drop electrode. Cyclic voltammetry was used to characterize the interfacial and redox behavior. Optimum experimental conditions were found to be the use of a stirred acetate buffer (pH 4.2) solution with a 2-(2′-thiazolylazo)- p -cresol concentration of 1.0 × 10 −5 M, a preconcentration potential of 0.00 V, a scan rate of 100 mV s −1 and a linear scan mode. The response is linear over the concentration range 5–30 μg V 5+ 1 −1 . For a 5-min preconcentration time, the detection limit is 3.9 nM. Possible interferences by anions and other trace metals were investigated. Sequential determination of copper with vanadium is possible. The method was applied to the analysis of mineral water.

Cathodic adsorptive stripping voltammetry of nickel complexed with hydroxynaphthol blue at a static mercury drop electrode

A new method is described for the determination of Ni based on the cathodic adsorptive stripping of Ni(II) complexed with hydroxynaphthol blue (HNB) at a static mercury drop electrode. Optimal conditions were found to be: accumulation potential -0.50 V (vs. Ag/AgCl); final potential -1.10 V; accumulation time 50 sec; scan rate 200 mV/sec; linear scan mode; filter 0.1 sec; supporting electrolyte acetic acid/acetate (0.25M, pH = 6.0) and concentration of HNB 3.3 x 10(-5)M. The response of the system was found to be linear in a range of Ni concentrations from 25 ppb to the detection limit. The detection limit was found to be 1.7 nM (0.10 ppb) with 2 mins of accumulation time. The effect of various potential interferences (including a variety of cations, anions and organic surfactants) were also studied. With the exception of Co, at less than equimolar concentrations no significant interferences were observed. Al was found to interfere at high concentrations with respect to Ni, but Al concentrations up to 1000 ppb may be masked by sodium citrate or sodium fluoride. The utility of the method is demonstrated by the recovery of Ni in a doped sample of commercial mineral water.

A study of the ditiophosphoric acid diacylester as a masking agent for the determination of bismuth in the presence of copper by hydride generation atomic absorption spectrometry

The masking action of the dithiophosphoric acid diacylester (DDTP) for the determination of Bi by hydride generation absorption spectrometry (HGAAS) in the presence of high concentrations of copper was studied. Cu/Bi ratios up to 50x10(3) were found to be tolerable in the presence of 2x10(-3) M chelating solutions in 10% HCl, using 1.5% NaBH(4) as reductant. Good agreement between the certified values and those found in the present study was verified in the analysis of certified reference materials.

Characterization and vapour phase interference studies of a flame heated holed quartz T-tube as atomization cell for hydride generation atomic absorption spectrometry

Characterization and mutual hydride forming element interference studies of a flame heated holed quartz T-tube as atomization cell for HGAAS were performed. Characteristic concentrations, limits of detection and linear ranges were determined for As, Bi, Sb and Se. Also, the mutual interferences of these elements were investigated. Extended non-interferent ranges were observed in most of the studied cases and such improvement was obtained at no great expense with regard to sensitivity and detection limits.

The use of 2-2-thiazolylazo-p-cresol to minimize the interference of Ni and Cu for the bismuth determination in alloys by hydride generation atomic absorption spectrometry

Thiazolylazo p-cresol (TAC) was studied as a masking agent for the determination of Bi in rich Ni and Cu alloys by hydride generation atomic absorption spectrometry (HGAAS). In the presence of TAC, Bi/Ni and Bi/Cu ratios up to 1:160 000 and 1:16 000, respectively, were found to be tolerable. No buffering was necessary once the masking agent was effective even in very acid medium. Limits of detection at the low mug g(-1) range were reached and the accuracy of the procedure was confirmed by the good concordance between found and certified values in the analysis of certified reference materials (CRM).

Determinação dos teores de zinco em diferentes extratos de hortaliças dos tipos A e B

O zinco e um elemento traco essencial as diversas funcoes bioquimicas do organismo humano. As interacoes fisico-quimicas entre nutrientes incluem: adsorcao, formacao de complexos e precipitacao, influenciando na biodisponibilidade. Atraves da determinacao do teor total do metal ingerido, nao e possivel medir o quanto deste metal sera absorvido. Entretanto, atraves da tecnica de especiacao dos metais, que e definida como a determinacao da concentracao das formas fisico-quimicas individuais dos elementos que, em conjunto, constitua a concentracao total do mesmo na amostra, podemos ter novos dados para prever sua absorcao. Para a especiacao em amostras solidas, inicialmente deve ser aplicado um metodo de extracao sequencial ou seletivo. Amostras de hortalicas dos tipos A e B foram analisadas quanto ao teor total de zinco atraves de espectroscopia de absorcao atomica em chama, e o metodo de extracao sequencial foi aplicado com os seguintes extratores: solucao de CaCl2 1M; solucao de acido acetico 0,1M; solucao de acido acetico 0,5M/acetato de amonio 5% [pH=5,0]; solucao de NaOH 0,1M e solucao de HCl 0,5M. Na analise da rejeicao de resultados foi aplicado o teste de Grubbs. Em 8 amostras a extracao do zinco foi considerada total, 6 amostras apresentaram extracao superior a 75%, 5 amostras extracao de 50% , amostra de quiabo teve 27% do total de zinco extraido e amostra de beterraba apenas 3%. Observa-se que para a maioria das amostras, o zinco se encontra sob a forma de no minimo 6 especies quimicas distintas. Estudos posteriores, que permitam a identificacao destas especies, favorecera a avaliacao da biodisponibilidade deste metal.

Avaliação do uso de ervas medicinais como suplemento nutricional de ferro, cobre e zinco

Copper, iron and zinc, considered essential elements in the human body, present changeable biodisponibility in chemical form more than if found in a food. Medicinal plants, widely used, can present new indications as to how much the suplementation of these metals, aiming at such an objective, can be shown to evaluate the amounts of copper, iron, and zinc in medicinal plants, powder and dry grass, and to promote the extraction sequencial aiming at the biodisponibility. The copper amount, iron and zinc had been determined through the spectroscopy of atomic absorption. The extraction sequencial was applied with the extractors calcium chloride 1,0M; acetic acid 0,1M with ammonium acetate 5% ( pH=5,0 ); acetic acid 0,5M and HCl 0,5M. The results had presented high copper amount, iron and zinc, when compared with other nourishing sources of these metals, besides indicating that the same ones if present under at the very least 4 distinct chemical species in the analyzed grass. The extracting (I) was of better efficiency for the three metals. Considering that the consumption of these grass is made with farmacological action, it is given credit that use of the same ones in foods can be used as fonts of these metals.