José Bento Borba da Silva

Determination of Ag, Pb and Sn in aqua regia extracts from sediments by electrothermal atomic absorption spectrometry using Ru as a permanent modifier

Ruthenium, deposited on a L’vov platform, is proposed as a permanent modifier for the determination of Ag, Pb and Sn in aqua regia extracts from sediments by electrothermal atomic absorption spectrometry. The coating process is simple: a solution containing Ru is pipetted repeatedly on to the platform inserted in a graphite tube and is submitted to a temperature program. In a 50% v/v aqua regia solution, high pyrolysis temperatures could be used: 1200 °C for Ag and Pb, and 1500 °C for Sn. At these temperatures, similar characteristic masses to those found for a nitric acid medium, using a Pd–Mg modifier, were obtained, showing that the high concentration of chloride does not interfere with the determination. In the aqua regia medium, the permanent modifier is much superior in comparison with Pd or Pd + Mg, modifiers applied as a solution, which could not stabilize the analytes satisfactorily. Very long tube lifetimes, around 1700 cycles, were obtained for Pb and Sn in this medium. Three sediment reference materials were partially dissolved using a mixture of aqua regia and hydrogen peroxide in a microwave oven. The results for Ag and Pb were in agreement with the recommended values, demonstrating the efficiency of the extraction. However, for Sn, the precison was less satisfactory, indicating that the extraction may be less efficient and reproducible for this analyte. Other advantages of the permanent Ru modifier are the low blanks due to in situ cleaning of the modifier and the shorter analysis time in comparison with the modifiers in solution.

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.

Oral Delivery of Meglumine Antimoniate-β-Cyclodextrin Complex for Treatment of Leishmaniasis

ABSTRACT The need for daily parenteral administration represents one of the most serious limitations in the clinical use of pentavalent antimonials against leishmaniasis. In this work, we investigated the ability of β-cyclodextrin to enhance the oral absorption of antimony and to promote the oral efficacy of meglumine antimoniate against experimental cutaneous leishmaniasis. The occurrence of interactions between β-cyclodextrin and meglumine antimoniate was demonstrated through the changes induced in the spin lattice relaxation times of protons in both compounds. When free and complexed meglumine antimoniate were given orally to Swiss mice, plasma antimony levels were found to be about three times higher for the meglumine antimoniate-β-cyclodextrin complex than for the free drug. Antileishmanial efficacy was evaluated in BALB/c mice experimentally infected with Leishmania amazonensis. Animals treated daily with the complex (32 mg of Sb/kg of body weight) by the oral route developed significantly smaller lesions than those treated with meglumine antimoniate (120 mg of Sb/kg) and control animals (treated with saline). The effectiveness of the complex given orally was equivalent to that of meglumine antimoniate given intraperitoneally at a twofold-higher antimony dose. The antileishmanial efficacy of the complex was confirmed by the significantly lower parasite load in the lesions of treated animals than in saline-treated controls. This work reports for the first time the effectiveness of an oral formulation for pentavalent antimonials.

Preconcentration of lead complexed with O, O-diethyl-dithiophosphate by column solid-phase extraction using different sorbents in a flow injection system coupled to a flame atomic absorption spectrometer

A comparative study of C(18) immobilized on silica, activated carbon and a polyurethane foam, as sorbents for Pb complexed with O,O-diethyl-dithiophosphate in a flow injection preconcentration system is reported. The complex was formed in 1.0 M HCl medium and processed in a simple system using a peristaltic pump, a manual injector-commutator and a mini-column filled with the sorbent. Using ethanol as eluent, the richest 150-mul fraction was collected and measured (after discarding 150, 200 and 0 mul for the activated carbon, foam and C(18), respectively) by flame atomic absorption spectrometry. The optimum concentration of the complexing agent was 0.05% m/v for C(18) and 0.2% m/v for the activated carbon and the polyurethane foam. The best sample loading flow rate was 4.0 ml min(-1) for the activated carbon and 2.0 ml min(-1) for C(18) and the polyurethane foam, while the best elution flow rate was 1.0 ml min(-1) (activated carbon) and 0.6 ml min(-1) (C(18) and foam). It was found that beyond a certain loading sample volume, for a constant analyte mass, the signal decreased. The maximum loading sample volume, for a constant analyte mass, before the signal started to decrease, was 50 ml for the activated carbon and 150 ml for the other materials. By processing 25 ml, the enrichment factors were 23, 55 and 166 for the activated carbon, foam and C(18), respectively. The best limit of detection (3sigma) was 0.3 mug l(-1) for the C(18) (1.2 mug l(-1) for the foam and 3 mug l(-1) for the activated carbon). As shown, the C(18) has a much superior retention performance in comparison to the other two materials.

Determination of As, Cd, Pb and Se in DORM-1 dogfish muscle reference material using alkaline solubilization and electrothermal atomic absorption spectrometry with Ir+Rh as permanent modifiers or Pd+Mg in solution

Abstract In this work, tetramethylammonium hydroxide (TMAH) was used to solubilize the DORM-1 dogfish muscle certified reference material as a model substance for the determination of As, Cd, Pb and Se by electrothermal atomic absorption spectrometry (ET AAS). The sample was mixed with a small amount of TMAH and heated to 60 °C for 10 min in a water bath. After dissolution, As and Se were determined using palladium and magnesium nitrates as a chemical modifier added in solution. For Cd and Pb, best results were obtained with a mixture of 250 μg of each of iridium and rhodium as permanent modifiers. In both cases, the calibration was performed with aqueous solutions in 0.2% v/v HNO 3 . The temperature program for each analyte was optimized using pyrolysis and atomization curves established with the fish reference material. The detection limits in dry samples and the characteristic mass values were: Cd 0.005 μg g −1 and 0.9 pg; Pb 0.04 μg g −1 and 7.6 pg; As 0.4 μg g −1 and 13 pg and Se 0.6 μg g −1 and 20 pg, respectively. Results from the determination of these elements in the DORM-1 certified fish reference material were within the 95% confidence interval of the certified values.

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 bismuth in aluminium and in steels by electrothermal atomic absorption spectrometry after on-line separation using a minicolumn of activated carbon

A simple on-line separation and preconcentration flow injection system for the determination of Bi in steels and aluminium solutions by electrothermal atomic absorption spectrometry is proposed. The system requires only a manual injector–commutator and a peristaltic pump. Bismuth is separated after complexation with the ammonium salt of dithiophosphoric acid O,O-diethyl ester and sorption in a minicolumn filled with activated carbon, using ethanol as eluent, which is received in the autosampler cup of the electrothermal atomic absorption spectrometer. A L’vov platform covered with 500 µg of Ir allows a pyrolysis temperature of 900 °C. The preconcentration, pre-elution and elution flow rates were optimized. The column was cleaned with 2 mL of ethanol followed by 5 mL of water. For 10 mL of sample solution, an enrichment factor of about 14 was obtained for Bi in Al or Fe matrices. The detection limit, in the sample solution, was 0.048 µg L–1. The linear regression coefficients of the calibration curves were better than 0.997. For the certified steel samples, the results were in agreement with the reference values. For the non-certified aluminium sample, the recoveries of spiked samples were in the range 87–105%. The fact that the complexing agent does not complex Al and Fe(II) allows the separation of more than 99.5% of the major components.

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.

Fast determination of chromium in human serum by electrothermal atomic absorption spectrometry

In this work, a group of chemical modifiers used in solution or as permanent modifiers were studied for the determination of chromium in human serum by ETAAS. The serum samples were diluted in the autosampler in the ratio 1 + 4 with 1% v/v nitric acid containing 0.02% v/v of cetyltrimethylammonium choride (CTAC). Formation of crusts in all the modifiers was prevented by addition of an optimized concentration of CTAC. Pyrolysis and atomization temperature curves were constructed for each modifier in the serum sample. For all the studied permanent modifiers (Ir, Ru, Zr and a mixture of Ir plus Rh) a plateau was obtained rather than peak formation, which, even for a 10 s atomization, did not return to the base line. With Pd + Mg, the peak was irregular and noisy and had a sensitivity about 4 times lower than that without modifier. The best results were obtained without a modifier, and with pyrolysis and atomization temperatures of 1000 and 2200 °C, respectively (characteristic mass of 0.6 ± 0.01 pg, recommended 8.0 pg without modifier for aqueous solutions). Calibration curves were similar using standard additions and aqueous solutions (with coefficients of 0.030 and 0.031, respectively). Three replicates of spiked serum samples were analyzed on three different days and the results were always close to 100%. The limit of detection (n = 10, k = 3) was 0.04 µg L−1. It was possible to run more than 300 cycles of atomization with a tube, without alteration in the signal and without the formation of crusts.

Direct determination of bismuth in urine samples by electrothermal atomic absorption spectrometry: study of chemical modifiers

In this work the performance of some chemical modifiers (no modifier, Pd + Mg, Ir in solution, Ru, Ir or Zr independently as permanent modifier and Ir + 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 µg of iridium, ruthenium and zirconium independently and 250 µg of Ir plus 250 µg of rhodium) was described elsewhere. Without modifier at all temperatures the signal was negative with a high background. Using Pd + Mg the best temperatures were of 1000 and 2500 °C, respectively, for pyrolysis and atomization, but the sensitivity was half that when using Ir + 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 °C, respectively, but the sensitivity was analogous with that obtained using Pd + Mg. Using Ir + Rh, the optimum pyrolysis and atomization temperatures were lower (900 and 1400 °C), 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 µg l−1, 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.