Arnaldo Alcover Neto

A simplified version of the total kjeldahl nitrogen method using an ammonia extraction ultrasound-assisted purge-and-trap system and ion chromatography for analyses of geological samples

The total Kjeldahl nitrogen (TKN) method was simplified by using a manifold connected to a purge-and-trap system immersed into an ultrasonic (US) bath for simultaneous ammonia (NH(3)) extraction from many previously digested samples. Then, ammonia was collected in an acidic solution, converted to ammonium (NH(4)(+)), and finally determined by ion chromatography method. Some variables were optimized, such as ultrasonic irradiation power and frequency, ultrasound-assisted NH(3) extraction time, NH(4)(+) mass and sulfuric acid concentration added to the NH(3) collector flask. Recovery tests revealed no changes in the pH values and no conversion of NH(4)(+) into other nitrogen species during the irradiation of NH(4)Cl solutions with 25 or 40 kHz ultrasonic waves for up to 20 min. Sediment and oil free sandstone samples and soil certified reference materials (NCS DC 73319, NCS DC 73321 and NCS DC 73326) with different total nitrogen concentrations were analysed. The proposed method is faster, simpler and more sensitive than the classical Kjeldahl steam distillation method. The time for NH(3) extraction by the US-assisted purge-and-trap system (20 min) was half of that by the Kjeldahl steam distillation (40 min) for 10 previously digested samples. The detection limit was 9 microg g(-1)N, while for the Kjeldahl classical/indophenol method was 58 microg g(-1)N. Precision was always better than 13%. In the proposed method, carcinogenic reagents are not used, contrarily to the indophenol method. Furthermore, the proposed method can be adapted for fixed-NH(4)(+) determination.

Determination of metals in coal fly ashes using ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry

A method for determination of Co, Cr, Cu, Fe, Mn, Ni, Ti, V and Zn in coal fly ash samples using ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) is proposed. The digestion procedure consisted in the sonication of the previously dried sample with hydrofluoric acid and aqua regia at 80 degrees C for 30 min, elimination of fluorides by heating until dryness for about 1h and dissolution of the residue with nitric acid solution. A classical digestion method, used as comparative method, consisted in the addition of HCl, HNO(3) and HF to 1 g of sample, and heating on a hot plate until dryness for about 6h. The proposed method presents several advantages: it requires lower amounts of sample and reagents, and it is faster. It is also advantageous when compared to the published methods, which also use ultrasound-assisted digestion procedure: lower detection limits for Co, Cu, Ni, V and Zn, and it does not require shaking during the digestion. The detection limits (microg g(-1)) for Co, Cr, Cu, Fe, Mn, Ni, Ti, V and Zn were 0.06, 0.37, 1.0, 25, 0.93, 0.45, 4.0, 1.7 and 4.3, respectively. The results were in good agreement with those obtained by the classical method and reference values. The exception was Cr, which presented low recoveries in classical and proposed methods (83 and 87%, respectively). Also, the concentration for Cu obtained by the proposed method was significantly different from the reference value, in spite of the good recovery (91+/-1%).

Simultaneous speciation of chromium by spectrophotometry and multicomponent analysis

Abstract A simple, fast and sensitive spectrophotometric method for the simultaneous determination of Cr(III) and Cr(VI) in effluents and contaminated waters using a UV-visible spectrophotometer, which operates with an advanced software for multicomponent analysis, is proposed. The method consists in the complexation of Cr (III) with EDTA and reaction of Cr(VI) with diphenylcarbazide (DPC). Variables, such as pH and colour stability time, were studied. The effect of concomitant ions on the simultaneous Cr(III) and Cr(VI) determination was also investigated. The sums of the chromium species concentrations obtained by the proposed method were compared with the total chromium concentrations found by electrothermal atomic absorption spectrometry. Recoveries of the chromium species between 75 and 136% were obtained for spiked samples. The linear working range for Cr(III) was 0.5-30 mg L−1, while for Cr(VI) was 0.005-0.30 mg L−1. The detection limits were 0.3 mg L−1 for Cr(III) and 0.003 mg L−1 for Cr(VI) while the quantification limits were 1.0 mg L−1 for Cr(III) and 0.01 mg L−1 for Cr(VI).

Determination of low‐molecular‐weight amines and ammonium in saline waters by ion chromatography after their extraction by steam distillation

A new method was developed for the determination of ammonium ion, monomethylamine and monoethylamine in saline waters by ion chromatography. Steam distillation was used to eliminate matrix interferences. Variables such as distillation time, concentration of sodium hydroxide solution and analyte mass were optimized by using a full two-level factorial (2(3) ) design. The influence of steam distillation on the analytical curves prepared in different matrices was also investigated. Limits of detection of 0.03, 0.05 and 0.05 mg/L were obtained for ammoniumion, monomethylamine and monoethylamine, respectively. Saline water samples from the Brazilian oil industry, containing sodium and potassium concentrations between 2.0-5.2% w/v and 96-928 mg/L, respectively, were analyzed. Satisfactory recoveries (90-105%) of the analytes were obtained for all spiked samples, and the precision was ≤ 7% (n = 3). The proposed method is adequate for analyzing saline waters containing sodium to ammoniumion, monomethylamine and monoethylamine concentration ratios up to 28 000:1 and potassium to ammonium, monomethylamine and monoethylamine concentration ratios up to 12 000:1.

Matrix-elimination with steam distillation for determination of short-chain fatty acids in hypersaline waters from pre-salt layer by ion-exclusion chromatography.

A method for determination of formic, acetic, propionic and butyric acids in hypersaline waters by ion-exclusion chromatography (IEC), using steam distillation to eliminate matrix-interference, was developed. The steam distillation variables such as type of solution to collect the distillate, distillation time and volume of the 50% v/v H₂SO₄ solution were optimized. The effect of the addition of NaCl different concentrations to the calibration standards on the carboxylic acid recovery was also investigated. Detection limits of 0.2, 0.5, 0.3 and 1.5 mg L⁻¹ were obtained for formic, acetic, propionic and butyric acids, respectively. Produced waters from petroleum reservoirs in the Brazilian pre-salt layer containing about 19% m/v of NaCl were analyzed. Good recoveries (99-108%) were obtained for all acids in spiked produced water samples.

Simulação do intemperismo natural de pilhas zinco-carbono e alcalinas

Spent alkaline and Zn-C batteries were placed in seawater, rainwater or landfill leachate at room temperature for up 30 days in order to simulate natural weathering. After the experiments pH and electrical conductivity of the liquid were measured. The precipitate formed and the filtrate were submitted to metal analysis by ICP-OES. Seawater is the most corrosive medium, followed by landfill leachate. Pb, Cd and Hg were mainly in the filtrate. Fe, Mn and Zn were generally dominant in the precipitate. Na and K account for the electrical conductivity and are good indicators of the corrosion stage of the batteries.

SÉRIE HISTÓRICA DA COMPOSIÇÃO QUÍMICA DE PILHAS ALCALINAS E ZINCO-CARBONO FABRICADAS ENTRE 1991 E 2009

Mn, Zn, Fe, Cd, Pb and Hg were determined in Zn-C and alkaline batteries manufactured along almost 20 years. After samples disassembly the electroactive components were treated with aqua regia in bath ice for 24 h. Metals were analyzed by ICP-OES. Zn and Mn amounts did not vary significantly. Fe amount decreased, specially after 2000. Hg, Cd and Pb amounts dramatically decreased along time, being virtually absent in alkaline batteries manufactured after 2005. Pb still remains in Zn-C samples. Scanning electron microscopy of batteries manufactured in 1997 and 1998 showed the presence of Bi, In and Cr in the plastic/paper anode-cathode separator.

A new on-line version of the gold amalgamation trap for interference-free determination of Hg0 in crude oil and related products by Zeeman CV-AAS

A new on-line version of the gold amalgamation trap was proposed for the determination of Hg0 in crude oil and related products prior to its detection by atomic absorption spectrometry. On-line analyses were carried out by a homemade gold amalgamation trap (GAT), heated at 120 °C during the Hg0 amalgamation, coupled to a commercial mercury analyzer, containing a spectral corrector based on the Zeeman effect. The heating avoided the collection of many volatile hydrocarbons onto the trap, and the Zeeman-effect corrector avoided the interferences caused by part of the organic vapors, which were collected onto the trap during the Hg0 amalgamation. Experimental parameters such as carrier gas flow, Hg0 release temperature and Hg0 amalgamation time were investigated. LOD and LOQ values of 0.06 and 0.21 μg L−1 Hg0 were obtained, respectively. Precision was always better than 10%. Quantitative Hg0 recoveries (85–116%) were obtained for the spiked certified reference materials and spiked crude oil, diesel and gas condensate samples.

Application of a purge-and-trap system for fixed-NH4+ determination by matrix interference free ion chromatography in oil reservoir rocks

A method for fixed-NH4+ determination using a system immersed into an ultrasonic bath for NH3 extraction and ion chromatography for NH4+ determination is proposed. The method is faster, simpler and more sensible (LOD = 4.4 mg g-1 NH4+) than the classical Kjeldahl method.

Fast and simultaneous ultrasound-assisted extraction of exchangeable-NH4+, NO3− and NO2− species from soils followed by ion chromatography determination

Abstract A method for the determination of exchangeable-ammonium, nitrate and nitrite species in soils by using a fast and simultaneous ultrasound-assisted extraction procedure followed by ion chromatography with conductimetric detection is proposed. Variables such as extraction method (ultrasonic bath or orbital shaker) and extractant type (water or acetic acid solution) were studied. The ultrasound-assisted reaction time was optimized. The best extraction efficiency was found when 0.5 g of soil sample was ultrasonically treated with 30 mL of acetic acid solution at pH 4.0 for 20 min. The results for acid soils or moderately basic (pH ≤ 8.1) were in agreement with those obtained by a classical method. The proposed method is preferable to the classical method because it is less laborious, faster, requires lower amount of sample and reagents and no carcinogenic reagent is used. The detection limits were 1.3 μg g-1 for NH4+–N, 0.06 μg g-1 for NO3-–N, and 0.08 μg g-1 for NO2-–N. The relative standard deviations were lower than 7% (n = 3) for all nitrogen species.