Multivariate approach in the optimization procedures for the direct determination of manganese in serum samples by graphite furnace atomic absorption spectrometry.

A method for direct determination of manganese (Mn) in human serum by graphite furnace atomic absorption spectrometry (GFAAS) was proposed in this work. The samples were only diluted 1:4 with nitric acid 1% (v/v) and Triton(®) X-100 0.1% (v/v). The optimization of the instrumental conditions was made using multivariate approach. A factorial design (2(3)) was employed to investigate the tendency of the most intense absorbance signal. The pyrolysis and atomization temperatures and the use of modifier were available and only the parameter modifier use did not have a significant effect on the response. A Center Composed Design (CCD) presented best temperatures of 430 °C and 2568 °C for pyrolysis and atomization, respectively. The method allowed the determination of manganese with a curve varying from 0.7 to 3.3 µg/L. Recovery studies in three concentration levels (n=7 for each level) presented results from 98 ± 5 to 102 ± 7 %. The detection limit was 0.2 µg/L, the quantifying limit was 0.7 µg/L, and the characteristic mass, 1.3 ± 0.2 pg. Intra- and interassay studies showed coefficients of variation of 4.7-7.0% (n=21) and 6-8%(n=63), respectively. The method was applied for the determination of manganese in 53 samples obtaining concentrations from 3.9 to 13.7 µg/L.

Speciation, distribution, and transport of mercury in contaminated soils from Descoberto, Minas Gerais, Brazil.

This work describes an investigation of mercury contamination in an abandoned gold mining site in the rural area of Descoberto, Minas Gerais, Brazil, whose inhabitants have reported "silver balls" present in the soil. Different granulometric fractions of soil samples and sedimented material from rainwater retention tanks in this area were analyzed for total mercury, organic matter, and mercury speciation by thermodesorption/atomic absorption spectrometry. The results showed mercury concentrations in the soils in the range of (0.0371-161) mg kg(-1), and the occurrence of Hg(0) oxidation. Some samples had concentrations as high as 90 mg kg(-1) with the majority as Hg(2+), which is important information in order to understand the biogeochemical behavior of mercury in contaminated sites and to apply the appropriate remediation technology. The retention boxes and tank samples showed that fine particles with high mercury content (3.3-90) mg kg(-1) are leached from the contaminated area, which reveals the need for efficient control of this material to prevent the contamination of stream waters. This study is an example that may be useful for other contaminated sites.

Determination of manganese in urine and whole blood samples by electrothermal atomic absorption spectrometry: comparison of chemical modifiers.

In this work, methodologies to determine manganese (Mn) in urine and whole blood by electrothermal atomic absorption spectrometry were developed. The use of Ru, Rh, and Zr as permanent modifiers, Pd as a modifier in solution, and the condition without modifier were investigated for the direct determination of Mn in urine and whole blood samples. The best results for Mn in urine and in whole blood were obtained without modifier use. The analytical characteristic, such as accuracy, precision and limit of detection of the proposed methodology were adequate.

Determination of cadmium, chromium and lead in marine sediment slurry samples by electrothermal atomic absorption spectrometry using permanent modifiers.

A procedure for the determination of cadmium, chromium, and lead in marine sediment slurries by electrothermal atomic absorption spectrometry is proposed. Slurry was prepared by mixing 10mg of ground sample with particle size smaller than 50 microm completed to the weight of 1.0 g with a 3% nitric acid and 10% hydrogen peroxide solution. The slurry was maintained homogeneous with an aquarium air pump. For cadmium, the best results were obtained using iridium permanent with optimum pyrolysis and atomization temperatures of 400 and 1300 degrees C, respectively, a characteristic mass, m(o) (1% absorption), of 2.3 pg (recommended 1 pg). Without modifier use, zirconium, ruthenium, and rhodium m(o) were 3.4, 4.1, 4.6, and 4.8 pg, respectively. For chromium, the most sensitive condition was obtained with zirconium permanent with optimum pyrolysis and atomization temperatures of 1500 and 2500 degrees C, m(o) of 6.6 pg (recommended 5.5 pg); and without modifier use, rhodium, iridium, and ruthenium m(o) were 5.3, 8.8, 8.8, and 8.9 pg, respectively. For lead, the best modifier was also zirconium, m(o) of 8.3 pg for the optimum pyrolysis and atomization temperatures of 600 and 1400 degrees C, respectively, (recommended m(o) of 9.0 pg). For iridium, ruthenium, without modifier, and rhodium, m(o) were 14.7, 15.5, 16.5, and 16.5 pg, respectively. For all the modifiers selected in each case, the peaks were symmetrical with r(2) higher than 0.99. Being analyzed (n=10), two marine sediment reference materials (PACS-2 and MESS-2 from NRCC), the determined values, microg l(-1), and certified values in brackets, were 2.17+/-0.05 (2.11+/-0.15) and 0.25+/-0.03 (0.24+/-0.01) for cadmium in PACS-2 and MESS-2, respectively. For chromium in PACS-2 and MESS-2 the values were 94.7+/-5.6 (90.7+/-4.6) and 102.3+/-10.7 (106+/-8), respectively. Finally, for lead in PACS-2 and MESS-2, the results obtained were 184+/-7 (183+/-8) and of 25.2+/-0.40 (21.9+/-1.2), respectively. For cadmium and lead in both samples and chromium in PACS-2, calibration was accomplished with aqueous calibration curves. For chromium in MESS-2, only with the standard addition technique results were in agreement with the certified ones. The limits of detection (k=3, n=10) obtained with the diluents were 0.1, 3.4, and 3.6 microg l(-1) for cadmium, chromium, and lead, respectively.

Direct determination of selenium in urine samples by electrothermal atomic absorption spectrometry using a Zr plus Rh-treated graphite tube and co-injection of Rh as chemical modifier.

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.

Development of methodologies to determine aluminum, cadmium, chromium and lead in drinking water by ET AAS using permanent modifiers.

In this work, methodologies were developed to determine aluminum (Al), cadmium chromium and lead in drinking water by electrothermal atomic absorption spectrometry using permanent modifiers. No use of modifier, iridium, ruthenium, rhodium and zirconium (independently, 500mug) were tested to each one analyte through the pyrolysis and atomization temperatures curves. As the matrix is very simple, did not had occurred problems with the background for all metals. The best results obtained for cadmium and chromium was with the use of rhodium permanent modifier. For lead and aluminum, the best choice was the use of zirconium. The selection for the modifier took into account the sensitivity, form of the absorption pulse and low atomization temperature (what contributes to elevate the useful life of the graphite tube). For aluminum using zirconium permanent, the best pyrolysis and atomization temperatures were respectively, of 1000 and 2500 degrees C with a characteristic mass (1% of absorbance, m(o)) of 19 pg (recommended of 20 pg). For cadmium, with use of rhodium the best temperatures for the pyrolysis and atomization were respectively of 400 and 1100 degrees C, with a symmetrical peak and with a m(o) of 1.0 pg (recommended of 1.0 pg). For chromium with rhodium permanent, the best temperatures for pyrolysis and atomization were respectively of 1000 and 2200 degrees C, with symmetrical peak and m(o) of 5.3 pg (recommended of 5.5 pg). For lead with zirconium permanent, the best temperatures for pyrolysis and atomization were of 700 and 2400 degrees C, with symmetrical peak and with m(o) of 30 pg (recommended of 20 pg). Water samples spiked with each one of the metals in four different levels inside of the acceptable values presented recoveries always close to 100%. The detection limits were of 0.1mugl(-1) for cadmium; 0.2mugl(-1) for chromium; 0.5mugl(-1) for lead and 1.4mugl(-1) for aluminum.

Determination of cadmium in biological samples solubilized with tetramethylammonium hydroxide by electrothermal atomic absorption spectrometry, using ruthenium as permanent modifier.

The feasibility of Ru as a permanent modifier for the determination of Cd in biological samples treated with tetramethylammonium hydroxide (TMAH) by ET AAS was investigated. The tube treatment with Ru was carried out only once and lasted for about 300 atomization cycles. The pyrolysis and atomization temperatures, 750 degrees C and 1300 degrees C, respectively, were chosen from the temperature curves. The sample dissolution procedure was very simple: a sample aliquot was mixed with a small volume of a 25% m/v TMAH solution, the volume was made up to 50 ml and the mixture was kept at 60 degrees C for 1 h. Six certified biological reference materials were analyzed and the obtained Cd concentrations are within the 95% confidence interval of the certified values, proving the accuracy of the proposed procedure for a variety of biological samples. The calibration curve, with correlation coefficient higher than 0.99, was established for a working range up to 10 microg l(-1). The precision was good as demonstrated by relative standard deviations below 3%, except for one sample. The limit of detection (3sigma) was 0.05 microg l(-1) and the characteristic mass was 1.30 pg, obtained in the presence of the Ru modifier.