Direct determination of arsenic in sugar by GFAAS with transversely heated graphite atomizer and longitudinal Zeeman-effect background correction

A method has been developed for the direct determination of As in sugar by graphite furnace atomic absorption spectrometry with a transversely heated graphite atomizer (end-capped THGA) and longitudinal Zeeman-effect background correction. The thermal behavior of As during the pyrolysis and atomization steps was investigated in sugar solutions containing 0.2% (v/v) HNO3 using Pd, Ni, and a mixture of Pd + Mg as the chemical modifiers. For a 60-muL sugar solution, an aliquot of 8% (m/v) in 0.2% (v/v)HNO3 was dispensed into a pre-heated graphite tube at 70 degreesC. Linear analytical curves were obtained in the 0.25 - 1.50-mug L-1 As range. Using 5 mug Pd and a first pyrolysis step at 600 degreesC assisted by air during 40 s, the formation of a large amount of carbonaceous residue inside the atomizer was avoided. The characteristic mass was calculated as 24 pg As and the lifetime of the graphite tube was around 280 firings. The limit of detection (L.O.D.) based on integrated absorbance was 0.08 mug L-1 (4.8 pg As) and the typical relative standard deviation (n = 12) was 7% for a sugar solution containing 0.5 mug L-1. Recoveries of As added to sugar samples varied from 86 to 98%. The accuracy was checked in the direct analysis of eight sugar samples. A paired t-test showed that the results were in agreement at the 95% confidence level with those obtained for acid-digested sugar samples by GFAAS.

Direct and simultaneous determination of As, Cu, and Pb in Brazilian sugar cane spirits by graphite furnace AAS using Tungsten permanent modifier with Co-injection of Pd/Mg(NO3)(2)

A method was developed using the multi-element graphite furnace atomic absorption spectrometry technique for the direct and simultaneous determination of As, Cu, and Pb in Brazilian sugar cane spirit (cachaqa) samples. Also employed was the end-capped transversely heated graphite atomizer (THGA) with platforms pre-treated with W permanent modifier and co-injection of Pd/Mg(NO3)(2). Pyrolysis and atomization temperature curves were established in a cachaqa medium (1+1; v/v) containing 0.2% (v/v) HNO3 and spiked with 20 mu g L-1 As and Pb and 200 mu g L-1 Cu. The effect of the concentration of major elements usually present in cachaqa matrices (Ca, Mg, Na, and K) and ethanol on the absorbance of As, Cu, and Pb was investigated. Analytical working solutions of As, Cu, and Pb were prepared in 10% (v/v) ethanol plus 5.0 mg L-1 Ca, Mg, Na, and K. Acidified to 0.2% (v/v) HNO3, these solutions were suitable to build calibration curves by matrix matching. The proposed method was applied to the simultaneous determination of As, Cu, and Pb in commercial sugar cane spirits. The characteristic mass for the simultaneous determination was 16 pg As, 119 pg Cu, and 28 pg Pb. The pretreated tube lifetime was about 450 firings. The limit of detection (LOD) was 0.6 mu g L-1 As, 9.2 mu g L-1 Cu, and 0.3 pig L-1 Pb. The found concentrations varied from 0.81 to 4.28 mu g L-1 As, 0.28 to 3.82 mg L-1 Cu and 0.82 to 518 mu g L-1 Pb. The recoveries of the spiked samples varied from 94-112% (As), 97-111% (Cu), and 95-101% (Pb). The relative standard deviation (n=12) was 6.9%, 7.4%, and 7.7% for As, Cu, and Pb, respectively, present in a sample at 0.87 mu g L-1, 0.81 mg L-1, and 38.9 mu g L-1 concentrations.

Direct determination of Al, As, Cu, Fe, Mn, and Ni in fuel ethanol by simultaneous GFAAS using integrated platforms pretreated with W-Rh permanent modifier together with Pd plus Mg modifier

A method is proposed for the simultaneous determination of Al, As, Cu, Fe, Mn, and Ni in fuel ethanol by electrothermal atomic absorption spectrometry (ETAAS) using W-Rh permanent modifier together with Pd(NO3)(2) + Mg(NO3)(2) conventional modifier. The integrated platform of a transversely heated graphite atomizer (THGA) was treated with tungsten, followed by rhodium, forming a deposit containing 250 mug W + 200 mug Rh. A 500-muL, volume of fuel ethanol was diluted with 500 muL, of 0.14 mol L-1 HNO3 in an autosampler cup of the spectrometer. Then, 20 muL, of the diluted ethanol was introduced into the pretreated graphite platform followed by the introduction of 5 mug Pd(NO3)(2) + 3 mug Mg(NO3)(2). The injection of this modifier was required to improve arsenic and iron recoveries in fuel ethanol. Calibrations were carried out using multi-element reference solutions prepared in diluted ethanol (1 + 1, v/v) acidified to 0. 14 mol L-1 HNO3. The pyrolysis and atomization temperatures of the heating program were 1200degreesC and 2200degreesC, respectively, which were obtained with multielement reference solutions in acidic diluted ethanol (1 + 1, v/v; 0. 14 mol L-1 HNO3). The characteristic masses for the simultaneous determination in ethanol fuel were 78 pg Al, 33 pg As, 10 pg Cu, 14 pg Fe, 7 pg Mn, and 24 pg Ni. The lifetime of the pretreated tube was about 700 firings. The detection limits (D.L.) were 1.9 mug L-1 Al, 2.9 mug L-1 As, 0.57 mug L-1.Cu, 1.3 mug L-1 Fe, 0.40 mug L-1 Mn, and 1.3 mug L-1 Ni. The relative standard deviations (n = 12) were 4%, 4%, 3%, 1.5%, 1.2%, and 2.2% for Al, As, Cu, Fe, Mn, and Ni, respectively. The recoveries of Al, As, Cu, Fe, Mn, and Ni added to the fuel ethanol samples varied from 81% to 95%, 80% to 98%, 97% to 109%, 85% to 107%, 98% to 106% and 97% to 103%, respectively. Accuracy was checked for the Al, As, Cu, Fe, Mn, and Ni determination in 10 samples purchased at a local gas station in Araraquara-SP City, Brazil. A paired t-test showed that at the 95% confidence level the results were in agreement with those obtained by single-element ETAAS.

A fast microwave-assisted, acid-vapor, steam-cleaning procedure for autosampler cups

A new and fast procedure is proposed for cleaning autosampler cups using acid-vapor steam-cleaning with a miniaturized assembly in a microwave-heated sealed Teflon vessel. A glass cactus-shaped holder was made to support six polyethylene autosampler cups (volume, 2.0 mt) inside a 100 mt microwave vessel. Regent-grade nitric acid was added to the vessels, and the system was heated in a microwave oven for 5 min at 300 W. Chromium was determined by graphite-furnace atomic-absorption spectrophotometry. The blank values were lower with cleaned cups compared to untreated cups (i.e., as received from supplier). The quantification limits, estimated from detection limits established with Milli-Q water, were 0.66 and 0.95 mu g Cr L-1 for cleaned and untreated auto-sampler cups, respectively. (C) 1998 Elsevier B.V. B.V. All rights reserved.

A hydride generation flow system for determination of arsenic and selenium by total reflection X-ray fluorescence spectrometry

In this work, a preconcentration and separation system based on continuous flow hydride generation is proposed to improve the determination of As and Se by total reflection X-ray fluorescence spectrometry. The generated hydrides are continuously separated from the liquid phase and collected in a chamber containing 250 mul of HCI/HNO3 1:1 (v/v) solution. Hydride generation conditions and collection of the hydrides were evaluated. Under optimised conditions, enrichment factors of 55 for As and 82 for Se were attained. Detection limits of 0.3 mug l(-1) for As and Se were obtained when 20 ml of sample was used. Analysis of a natural water standard reference material from National Institute of Standard and Technology (SRM-1640) was in agreement with the certified values at the 95% confidence level. (C) 2004 Elsevier B.V. All rights reserved.

Thermogravimetry (TG) applied to the study of the reaction of mercury with platinum-rhodium alloy

Thermogravimetry (TG) energy dispersive X-ray microanalysis (EDX), scanning electron microscopy (SEM), mapping surface, X-ray diffraction (XRD), inductively coupled plasma emission spectroscopy and atomic spectroscopy with cold vapor generation have been used to study the reaction of mercury with platinum-rhodium (Pt-Rh) alloy. The results suggest that, the electrodeposited Hg film reacts with Pt-Rh to form intermetallic compounds of different stability, when heated indicated by at least four weight loss steps. Intermetallic compounds as PtHg4 and PtHg2 was characterized by XRD. These intermetallic compound are the main product presents on the surface of the samples after remotion of the bulk mercury via thermal desorption techniques. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Flow injection AAS determination of Cd, Cu, and Pb at trace levels in wine using solid phase extraction

A comparative study is reported between C-18 bonded silica gel and powdered polyethylene (PE) as sorbent for Cd, Cu, and Pb determination using ammonium diethyldithiophosphate (ADTP) as the complexing agent in a flow injection system. The complexes were formed in 0.14 mol L-1 HNO3 and processed in a simple flow system comprising a peristaltic pump, a manual injector-commutator, and a sorbent-packed minicolumn. Ethanol was selected as the eluent and analytes in the eluate were determined by flame atomic absorption spectrometry. The optimum concentration of the complexing agent was 0.1% (m/v) ADTP for Cu and Pb determination using either C-18 or PE, and 0.25% (m/v) ADTP for Cd determination using PE. The sample loading flow rates were 5.0, 3.6, and 3.0 mL min(-1) for Cu, Pb, and Cd, respectively. The best elution flow rate was 6.5 mL min(-1). For a 60-sec preconcentration time, the sampling rate was 40 h(-1) and the enrichment factors of 33, 36, and 11 times (C-18) or 18, 22, and 23 times (PE) were obtained for Cu, Pb, and Cd, respectively. The limits of detection (LOD) were 1.6 mug L-1 Cu, 11 mug L-1 Pb, and 2.0 mug L-1 Cd using C-18 or 2.9 mug L-1 Cu, 19 mug L-1 Pb, and 1.0 mug L-1 Cd using PE, respectively. The relative standard deviations (n = 12) were typically <2%, <2%, and <6% for Cd, Cu, and Pb, respectively. The recoveries of Cd, Cu, and Pb added to wine samples varied from 96-99%, 97-102%, and 90-99%, respectively, using C-18 or PE. Accuracy was checked for Cd, Cu, and Pb determination in six wine samples digested by block digestor and open-vessel microwave-assisted digestion systems. The results revealed that C-18 was more efficient for Cu and Pb determination, while PE was the best sorbent for Cd.

Evaluation of sample treatment for the simultaneous flow injection hydride generation and determination of As, Bi, Sb and Se by GRAS

A new method was developed for the simultaneous determination of As, Bi, Sb, and Se by flow injection hydride generation graphite furnace atomic absorption spectrometry. An alternative two-step sample treatment procedure was used. The sample was heated (80degreesC) for 10 min in 6 M HCl to reduce Se(VI) to Se(IV), followed by the addition of 1% (m/v) thiourea solution to reduce arsenic and antimony from the pentavalent to the trivalent states.With this procedure, all analytes were converted to their most favorable and sensitive oxidation states to generate the corresponding hydrides. The pre-treated sample solution was then processed in the flow system for in situ trapping and atomization in a graphite tube coated with iridium. The impermanent modifier remained stable up to 300 firings and new coating out significant were possible wit changes in the analytical performance.The accuracy was checked for As, Bi, Sb, and Se determination in water standard reference materials NIST 1640 and 1643d and the results were in agreement with the certified values at a 95% confidence level. Good recoveries (94-104%.) of spiked mineral waters and synthetic As(V), Sb(Ill), mixtures of As(Ill), Sb(V), Se(VI), and Se(IV) were also found. Calculated characteristic masses were 32 mug As, 79 mug Bi, 35 mug Sb, and 130 pg Se, and the corresponding limits of detection were 0.06, 0.16, 0.19, and 0.59 mug L-1, respectively. The repeatability for a typical solution containing 5 mug L-1 As, Bi, Sb, and Se was in the 1-3% range.

Analysis of cement slurries by inductively coupled plasma optical emission spectrometry with axial viewing

The feasibility of Portland cement analysis by introduction of slurries in an inductively coupled plasma optical emission spectrometer (ICP-OES) with axial viewing has been evaluated. After a fast manual grinding of the cement samples, owing to the pulverized state of this material, 0.1% m/v slurries were prepared in 1% v/v HCl. The calibration was performed adopting two strategies: one based on slurries prepared from different masses (50, 75, 100 and 125 mg) of a Portland cement standard reference material (NIST SRM 1881), and the other one based on aqueous reference solutions. A complete analysis of cement for major (Al, Ca, Fe, Mg and Si), minor and trace elements (Mn, P, S, Sr and Ti) was accomplished. Both strategies led to accurate results for commercial Portland cement samples, except for Si and Ti. for which the calibration with aqueous reference solutions resulted in low values. Applying a paired t-test it was shown that most results were in agreement at a 95% confidence level with a conventional fusion decomposition procedure. The ICP-OES with axial viewing and end-on gas configuration for removal of the recombination plasma zone was effective for cement slurry analysis without any undesirable particle deposition in the pre-optics interface and without severe spectral interferences. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Paper-based diffusive gradients in thin films technique coupled to energy dispersive X-ray fluorescence spectrometry for the determination of labile Mn, Co, Ni, Cu, Zn and Pb in river water

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Highly excited states for the helium atom in the hyperspherical adiabatic approach

The hyperspherical adiabatic approach is used to obtain the highly excited series 1sns 1S e and 1s(n + 1)p 1P o of the helium atom. The introduction of appropriate asymptotic conditions at large values of the hyperspherical radius results in a stable algorithm that allows the calculation of the full atomic spectrum with precision of a few parts per million. Comparison with the variational calculations available in the literature shows that the accuracy of the results improves with increasing principal quantum number. We present the energies up to n = 31 which is the typical value used in multiphoton excitation experiments.

Contribution to the study of the solid-state reaction of mercury with pure rhodium

Thermogravimetry (TG) and other analysis techniques (EDX, SEM, Mapping surface, X-ray diffraction, inductively coupled argon plasma emission spectroscopy and atomic spectrometry with cold vapor generation) were used to study the reaction of Hg with Rh. The results permitted the suggestion that, when subjected to heat, an electrodeposited Hg film reacts with Rh to form intermetallic products with different stabilities, as indicated by at least three mass loss steps. In the first step, between room temperature and 160°C, only the bulk Hg is removed. From this temperature up to about 175°C, the mass loss can be attributed to the desorption of a film of metallic Hg. The last step, from 175 to 240°C, can be ascribed to the removal of Hg from a thin dark film of RhHg2.

Simultaneous determination of As, Cu, Mn, Sb, and Se in drinking water by GFAAS with transversely heated graphite atomizer and longitudinal zeeman-effect background correction

A method has been developed for the direct and simultaneous determination of As, Cu, Mn, Sb, and Se in drinking water by electrothermal atomic absorption spectrometry (ETAAS) using a transversely heated graphite tube atomizer (THGA) with longitudinal Zeeman-effect background correction. The thermal behavior of analytes during the pyrolysis and atomization stages was investigated in 0.028 mol L-1 HNO3, 0.14 mol L-1 HNO3 and 1 + 1 (v/v) diluted water using mixtures of Pd(NO3)2 + Mg(NO3)2 as the chemical modifier. With 5 μg Pd + 3 μg Mg as the modifier, the pyrolysis and atomization temperatures of the heating program of the atomizer were fixed at 1400°C and 2100°C, respectively, and 20 μL of the water sample (sample + 0.28 mol L-1 HNO3, 1 + 1, v/v), dispensed into the graphite tube, analytical curves were established ranging from 5.00 -50.0 μg L-1 for As, Sb, Se; 10.0 - 100 μg L-1 for Cu; and 20.0 - 200 μg L-1 for Mn. The characteristic masses were around 39 pg As, 17 pg Cu, 60 pg Mn, 43 pg Sb, and 45 pg Se, and the lifetime of the tube was around 500 firings. The limits of detection (LOD) based on integrated absorbance (0.7 μg L-1 As, 0.2 μg L-1 Cu, 0.6 μg L-1 Mn, 0.3 μg L-1 Sb, 0.9 μg L-1 Se) exceeded the requirements of the Brazilian Food Regulations (decree # 310-ANVS from the Health Department), which established the maximum permissible level for As, Cu, Mn, Sb, and Se at 50 μg L-1, 1000 μg L-1, 2000 μg L-1, 5 μg L-1, and 50 μg L-1, respectively. The relative standard deviations (n = 12) were typically < 5.3% for As, < 0.5% for Cu, < 2.1% for Mn, < 11.7% for Sb, and < 9.2% for Se. The recoveries of As, Cu, Mn, Sb, and Se added to the mineral water samples varied from 102-111%, 91-107%, 92-109%, 89-97%, and 101-109%, respectively. Accuracy for the determination of As, Cu, Mn, Sb, and Se was checked using standard reference materials NIST SRM 1640 - Trace Elements in Natural Water, NIST SRM 1643d - Trace Elements in Water, and 10 mineral water samples. A paired t-test showed that the results were in agreement with the certified values of the standard reference materials at the 95% confidence level.

Rapid determination of zinc in foods by flow injection analysis with flame AAS using gradient calibration method

A calibration method was developed using flow injection analysis (FI) with a Gradient Calibration Method (GCM). The method allows the rapid determination of zinc In foods (approximately 30 min) after treatment with concentrated sulphuric acid and 30% hydrogen peroxide, and analysis with flame atomic absorption spectrometry (FAAS). The method provides analytical results with a relative standard deviation of about 2% and requires less time than by conventional FI calibration. The electronic selection of different segments along the gradient and monitoring of the technique covers wide concentration ranges while maintaining the inherent high precision of flow injection analysis. Concentrations, flow rates, and flow times of the reagents were optimized in order to obtain best accuracy and precision. Flow rates of 10 mL/min were selected for zinc. In addition, the system enables electronic dilution and calibration where a multipoint curve can be constructed using a single sample injection.

Direct and simultaneous determination of As, Cu, and Pb in Brazilian sugar cane spirits by graphite furnace AAS using tungsten permanent modifier with co-injection of Pd/Mg(N03)2

A method was developed using the multi-element graphite furnace atomic absorption spectrometry technique for the direct and simultaneous determination of As, Cu, and Pb in Brazilian sugar cane spirit (cachaça) samples. Also employed was the end-capped transversely heated graphite atomizer (THGA) with platforms pre-treated with W permanent modifier and co-injection of Pd/Mg(N03)2. Pyrolysis and atomization temperature curves were established in a cachaça medium (1+1; v/v) containing 0.2% (v/v) HN03 and spiked with 20 μg L-1 As and Pb and 200 μg L-1Cu. The effect of the concentration of major elements usually present in cachaça matrices (Ca, Mg, Na, and K) and ethanol on the absorbance of As, Cu, and Pb was investigated. Analytical working solutions of As, Cu, and Pb were prepared in 10% (v/v) ethanol plus 5.0 mg L-1 Ca, Mg, Na, and K. Acidified to 0.2% (v/v) HNO3, these solutions were suitable to build calibration curves by matrix matching. The proposed method was applied to the simultaneous determination of As, Cu, and Pb in commercial sugar cane spirits. The characteristic mass for the simultaneous determination was 16 pg As, 119 pg Cu, and 28 pg Pb. The pretreated tube lifetime was about 450 firings. The limit of detection (LOD) was 0.6 μg L-1As, 9.2 μg L-1 Cu, and 0.3 μg L-1Pb. The found concentrations varied from 0.81 to 4.28 μg L-1As, 0.28 to 382 mg L-1 Cu and 0.82 to 518 μg L-1 Pb. The recoveries of the spiked samples varied from 94-112% (As), 97-111% (Cu), and 95-101% (Pb). The relative standard deviation (n=12) was 6.9%, 7.4%, and 7.7% for As, Cu, and Pb, respectively, present in a sample at 0.87 μgL-1, 0.81 mgL-1, and 38.9 μgL-1concentrations.