Electrothermal Atomization Atomic Absorption Spectrometry Research Articles

Ultrasound Accelerated Solid-Liquid Extraction for the Determination of Selenium in Biological Samples by Electrothermal Atomization Atomic Absorption Spectrometry

A novel method for sample preparation by ultrasound-accelerated solid-liquid extraction prior to selenium determination in the phosphate-rich biological samples by electrothermal atomization atomic absorption spectrometry (ETAAS) with continuum-source background correction and nickel nitrate as a chemical modifier was established and compared with the results of conventional sample wet decomposition (however, this last item was not the object of this study). Diluted (4%) nitric acid was used as an extraction medium. The evaluation of the analytical results for biological Certified Reference Materials indicates that the results of a selenium determination after wet acid digestion (HNO3+HCl+H2O2) agreed well with the certified values, whereas the proposed solid-liquid extraction procedure can be used for simple and rapid control of the selenium levels.

A Generalized Method for the Determination of Nickel in Different Samples by ETAAS After Rapid Microwave-Assisted Digestion

ABSTRACT Determination of nickel has been carried out by electrothermal atomization atomic absorption spectrometry (ETAAS) using unpyrocoated tubes. A generalized method has been developed for quantitative determination of total nickel in different types of samples: geological, like rock, soil and sediment, environmental, like sewage sludge, and biological, like mussel tissue and rice flour, after their rapid microwave-assisted digestion. The systematic study of the effect of six different matrix modifiers demonstrated that, using an ashing temperature of 1000°C and carrying out the atomization at 2700°C, neither modifier nor background correction are necessaries. The recommended procedure is based on the pressurized acid digestion of samples with aqua regia, HF and H2O2, in different steps, inside hermetically closed teflon reactors, heated by radiation in a microwave oven, at power levels between 330 and 550W. After the complete dissolution of samples, Ni is determined by ETAAS carrying out the absorbance measurements in the peak height mode, and using aqueous solutions of Ni as standards.

New Standardless Method of Pb Analysis by Electrothermal Atomic Absorption Spectroscopy in Air Aerosols: Comparison with the Official Method

A standardless analysis method with electrothermal atomization/atomic absorption spectroscopy (ETA-AAS) measurements is proposed and applied to the determination of Pb in an urban environment (Bologna, Italy) and compared with results obtained in the same place and time, with the method dictated by Italian law, which is derived by European Community Directives. It was found that the difference previously observed between the two methods is due to the low efficiency of the 0.45-μm-pore-size paper filters, dictated by the official method. The uncovering of the error source validates the proposed method and highlights its accuracy. Moreover, the two methods can be conveniently combined to give two series of data relevant to pollutants associated with low- and high-dimension particles. This capability gives a much more precise picture of the hazard of a pollutant.

Use of Graphite Furnace Television in Electrothermal Atomization Atomic Absorption Spectrometry

The determination of metals in traces by means of electrothermal atomization atomic absorption spectrometry (ETA-AAS) presents analytical difficulties for complex matrixes such as seawater or brines. Some of them can be overcome with sample pretreatment or through the use of matrix modifiers at the moment of the instrumental analysis. These operations require a preliminary study of the working conditions, the effect of which is evaluated through the trend of the background signal, the signal-to-noise ratio, and the recovery of analytes after a given pretreatment. The optimization of the first two aspects is generally achieved for attempts through monitoring of the signals produced by the photomultiplier in correspondence of the total and aspecific absorptions. To this purpose the use of a solid state CCD camera like an ancillary device was applied to the development of the thermal program. The television camera was temporarily lined with the furnace during the drying and ashing phases. Detailed images of the phenomena related to the phase transitions occurring in graphite furnace prior to atomization were thus obtained.

Selenium speciation by coupling vesicle mediated HPLC with off-line ETAAS and on-line focused microwave digestion HG-AAS detection.

A novel High Performance Liquid Chromatography (HPLC) method for the separation of selenium species with specific detection by off-line Electrothermal Atomization Atomic Absorption Spectrometry (ETAAS) or on-line focused microwave digestion (MW) Hydride Generation Atomic Absorption Spectrometry (HG-AAS) is described. Vesicular mobile phases of the cationic surfactant didodecyldimethylammonium bromide (DDAB) have been evaluated for the liquid chromatographic separation of inorganic selenium (selenite and selenate) and different selenoaminoacids (selenocystine, selenomethionine and selenoethionine) on a C(18) reversed-phase column modified by DDAB molecules. The effects of different parameters (pH, buffer and vesicle concentrations) of the mobile phase on the retention times have been determined. The detection limit for selenium with the proposed off-line HPLC-ETAAS method has been found to be 5 microg/L of Se. The detection limit using HPLC-"on line" focused microwave digestion-HG-AAS has been found to be 1 microg/L of Se, with a precision (repeatability) better than +/- 5%. The latter proved to be an exceptional on-line real-time chromatographic detector for selenium speciation purposes.

A New Method for Standardless Analysis in ETA-AAS Applied to the Determination of Lead Associated with Air Aerosol

The analysis ofPbassociated with air aerosols by its accumulation through electrostatic precipitation directly in a graphite tube, which is subsequently used as an atomizer in electro thermal atomization-atomic absorption spectroscopy (ETA-AAS), has already been tested and found very convenient for its simplicity and speed. However, its use as a practical and useful method of analysis was hampered by the necessity of a laborious and difficult calibration with high risks of systematic errors. These difficulties can be bypassed by resorting to an absolute or standardless method of analysis. Standardless methods of analysis have been proposed for ETA-AAS measurements and recently applied toCdandHg.With the use of a new and more powerful power supply this method has been extended toPbso that a very easy, fast, and almost on line way of measuring the level ofPbin air aerosols is possible. The system presented in this paper is manually operated but its automation, in order to obtain an automatic control station, is only a matter of convenience.

Cadmium levels in wine, beer and other alcoholic beverages: possible sources of contamination

An accurate and precise method is described for the direct determination of Cd in wine, beer and other alcoholic beverages by electrothermal atomization-atomic absorption spectrometry (ETA-AAS). The graphite furnace program was optimized and samples were pretreated with nitric acid and pentoxide vanadium in a digestion block at 120°C for 90 min. The results obtained were validated against microwave acid sample digestion. The analytical detection limit was 0.5 pg. The proposed method was applied to determine Cd in 134 samples of 10 different alcoholic beverages. The mean values ranged from 0.10 to 15.38 μg/l in wine, from not detectable to 0.80 μg/l in beer, and from not detectable to 11.52 μg/l in other alcoholic beverages such as cider, brandy, rum, whisky, gin, anisette, liquor and spirits. The wide variability of the results obtained emphasizes the multiplicity of factors than can influence the presence of Cd in these products. Because alcoholic beverages are widely consumed, they contribute a large fraction of cadmium intake, and therefore, strict control of this element is advisable.

Anodic stripping voltammetric determination of total lead in anencephalic fetuses after pressure/temperature-controlled microwave mineralization

The development of a closed-vessel mineralization method for the decomposition of brain, liver, kidney and lung specimens of anencephalic (A) fetuses and controls (C) from the eastern coast of lake Maracaibo, Venezuela, is presented. Digestion was done in a laboratory microwave oven provided with pressure sensing tube and fiberoptic temperature probe to monitor and control pressure and temperature conditions inside the lined digestion vessels. Total lead was subsequently determined by differential pulse anodic stripping voltammetry (DPASV) with a hanging mercury drop electrode. The optimized conditions for maximal pressure and temperature set up were 1260 kPa and 190 °C. Three samples and one blank were routinely prepared for simultaneous digestion. After sample mineralization, the lead oxidation peak appeared at a potential of −0.45 V vs. Ag AgCl , pH 4.70. Lead concentrations obtained by DPASV analysis of the mineralized biological materials were compared with those provided by electrothermal atomization atomic absorption spectrometry (ETA-AAS) on the same digestion samples. The correlation between the two methods was excellent: y = 1.142 x − 0.0035, r = 0.9999, n = 40, p < 0.001, where y and x were the lead concentrations determined by DPASV and ETA-AAS, respectively. For the DPASV determination of total lead, precision (R.S.D.) was better than 3.8%, for within- and between-run analyses. The detection limit of the electrochemical method, defined as three times the standard deviation of a blank solution, was 0.03 μg Pb g −1 (in solid sample), equivalent to 0.1 μg Pb l −1 in the diluted test portions. The dry-weight metal concentrations (± 1 S.D., μg g −1) found in brain, liver, kidney and lung were as follows: (brain, undetectable in A and in C; liver, 2.1 ± 1.1 in A, 0.5 ± 0.2 in C; right lung, 1.1 ± 0.8 in A, 0.6 ± 0.1 in C; left lung, 0.6 ± 0.2 in A, 0.7 ± 0.1 in C; right kidney, 1.4 ± 0.7 in A, 1.5 ± 0.03 in C and left kidney, 1.7 ± 0.9 in A, 0.7 ± 0.2 in C. The proposed DPASV method constitutes an analytical alternative, as reliable as ETA-AAS, for the voltammetric determination of total lead in solid samples.

High current power supply for electrothermal atomic absorption spectrometry

A new power supply for electrothermal atomization — atomic absorption spectrometry (ETA-AAS) with associated equipment for temperature control is presented. The system is composed of two high current commercial batteries and a MOSFET switch which controls the temperature of the atomizer by switching the current in an on-off way through a feedback loop connected to a personal computer and suitably programmed peripherals. The delivered power can be changed from 0 to 100% in 1% steps which gives the possibility of roughly controlling both the temperature at low power when the temperature sensor is not working and the heating rate. With this system, curves for which the simultaneous presence of all atoms injected in the atomizer is claimed, have been extended to Pb, Ag, Tl and Zn. With a more conventional power supply previously used, such a claim could be made only for Cd and Hg.

Signal processing of transient atomic absorption signals

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hard copy text is accompanied by a disk with a demonstration version of the simulation program, libraries of electronic and optical component blocks, simulation models, manual, and other files. Absorbance signals for electrothermal atomization atomic absorption spectroscopy (ETA-AAS) were generated digitally and the effect of various types and sources of noise upon the precision of the absorbance measurement was evaluated by numerical calculation. Peak area measurement, peak height measurement, and matched filtering were used for processing these signals. The performance of these three techniques in the presence of various types of noises and the sensitivity of each to small variation in the atomization conditions was calculated. It is demonstrated that significant improvement in signal-to-noise ratios can be realized by application of appropriate signal processing methods. The results also indicate that one of the principal causes for loss of precision could be the variation in the heating characteristics of the furnace.

Determination of Chromium(III) and Chromium(VI) by Electrothermal Atomization Atomic-Absorption Spectrometry Following Coprecipitation with Gallium(III) Phosphate

Abstract Gallium(III) phosphate coprecipitates quantitatively 0.2—7.5 μg of chromium(III) from 100 to 500 cm3 of a sample solution at pH 4.5—6.0. Although chromium(VI) is hardly coprecipitated with gallium(III) phosphate, it can be collected as chromium(III) after reduction by hydroxylamine. The calibration curve is linear from 8 to 300 ng cm−3 for chromium. The detection limit (signal/noise = 2) is 0.11 ng cm−3 of chromium(III) or chromium(VI) in 500 cm3 of the initial sample solution.

A comparison of copper speciation results obtained using electrothermal atomization atomic absorption spectrometry and computer modelled data

A comparative study is described between the direct determination of copper species obtained by electrothermal atomization atomic absorption spectrometry (ETAAS) and the predicted data using the NSPEC computer speciation program. Inorganic copper nitrate and copper citrate species were determined at different pH levels using ETAAS following a range of solid-phase extraction procedures. The results indicated that the NSPEC speciation program and experimental data identified the anionic species to be dominant. For a relatively simple system the NSPEC program can therefore be used to compare theoretical data with experimental data.

A spectral interference in the determination of arsenic in high-purity lead and lead-base alloys using electrothermal atomic absorption spectrometry and Zeeman-effect background correction

Arsenic, antimony, and tellurium are determined at part-per-million concentration levels in bullet lead, lead-base alloy, and high purity lead using electrothermal atomization atomic absorption spectrometry (ETAAS) with Zeeman-effect background correction. A spectral interference by lead absorption lines resulting from excited state transitions is observed on both primary arsenic analysis lines, at 193.696 nm and 197.197 nm. Analytical bias caused by the interference at 197.197 nm is eliminated by using temperature programming and temporal resolution.

Trace Metal Assay of Uranium Silicide Fuel

A comprehensive trace metal assay of uranium silicide, a fuel for nuclear research reactors that employs low-enrichment uranium, is carried out by atomic spectrometry. Of the list of specification elements, 21 metallic elements are determined by a direct current (dc) arc carrier distillation technique; the rare earths yttrium and zirconium are chemically separated from the major matrix followed by a dc arc/inductively coupled argon plasma (ICP) excitation technique in atomic emission spectrometry (AES); silver is determined by electrothermal atomization-atomic absorption spectrometry (ETA-AAS) without prior chemical separation of the major matrix. Gamma radioactive tracers are used to check the recovery of rare earths during the chemical separation procedure. The detection limits for trace metallics vary in the 0.1- to 40-ppm range. The precision of the determinations as evaluated from the analysis of the synthetic sample with intermediate range analyte concentration is better than 25% relative standard deviation (RSD) for most of the elements employing dc arc-AES, while that for silver determination by ETS-AAS is 10% RSD. The precision of the determinations for four crucially important rare earths by ICP-AES is better than 3% RSD.

Direct determination of tin in tap waters by electrothermal atomization atomic absorption spectroscopy

A method is described for the direct determination of tin in tap waters by electrothermal atomization atomic absorption spectroscopy (ETA-AAS), using magnesium-nitric acid and palladium-magnesium as chemical modifiers. The charring and atomization temperatures and times, and the amount of modifier were optimized. The calibration and addition graphs, detection limit, quantitation limit, precision, accuracy, interferences and characteristic mass were also investigated. The method was applied to the determination of tin in tap water samples.

Direct determination of beryllium, copper and zinc in AlU matrices by electrothermal atomization atomic-absorption spectrometry

An atomic-absorption spectrometric method with electrothermal mode of atomization has been developed for the direct determination of Be, Cu and Zn in AlU (3:1) matrix samples without prior chemical separation of the major matrix. The studies carried out include the effect of the matrix on the analyte absorbance, optimization of sample aliquot and other experimental parameters, and analysis of a number of synthetic samples. Nanogram amounts of the analytes can be determined with a solution aliquot of 5 microlitres containing 25 micrograms of the sample with a precision of 6% or better. The analytical range obtained for these analytes is Be: 2–20 μg/l., Cu: 20–200μg/l. and Zn: 1–40μg/ml in the AlU matrix. The analysis of synthetic samples has shown good agreement with their added contents.

Lead and Nickel Levels in Black Sea Aerosols by Eta-Aas

Abstract Air particulate samples were collected from the Black Sea atmosphere, using cellulose filters in the summer of 1988. Lead and nickel concentrations in aerosols collected at 10 m above sea level were determined by using electrothermal atomization atomic absorption spectrometry (ETA-AAS). Concentrations of Pb and Ni were high in the western part of the Black Sea, owing to strong influence of anthropogenic sources. Lead was highly enriched in the Black Sea aerosols due to the significant contribution of motor vehicle emissions, while Ni was moderately enriched. The Pb/Br ratio was higher than the corresponding ratio in fresh motor vehicle emissions, owing to evaporation of Br from particles. Atmospheric flux of Pb to the Black Sea was higher than riverain flux, while the opposite was observed for Ni.

A method for the determination of the kinetic order and energy of the atom formation process in electrothermal atomization atomic absorption spectrometry (ETA-AAS)

A procedure for the determination of the kinetic parameters for the atom formation process in electrothermal atomizers is presented. From the kinetic equations of a mechanism where the rate of atom formation is assumed to have an arbitrary order m, we obtained that the rate constant for the non-isothermal generation of atomic vapor k 1( t) is proportional to: ▪ where k 2( t) is the rate constant for the dissipation of the atomic vapor and A( t) is the absorbance signal. An Arrhenius type plot of log Wm(t), calculated with the experimental absorbance data, as a function of the inverse of the time dependent atomization temperature, gives a linear curve for the appropriate order m and allows the determination of the atomization energy E a. A comparison with other methods is made and the deviations from linearity of the Arrhenius plots, commonly found in the literature, are discussed. The results obtained for the electrothermal atomization of Ru, Cu, Ni and Li are presented.

Speciation of Cr(VI)/Cr(III) by electrothermal atomisation AAS after electrodeposition on a L'vov platform

The pyrolysed graphite L'vov platform of a tube furnace is considered as an electrode for the electrodeposition and speciation of chromium by electrothermal atomisation atomic absorption spectrometry (ETA-AAS). Firstly, a preliminary study of the Cr(VI)/Cr(III) voltammetric behavior at pH 4.70 on a glassy-carbon electrode is carried out. Secondly, the L'vov platform is used as a cathodic macro-electrode for the selective preconcentration of Cr(VI)/Cr(III) on a mercury film. Speciation of Cr(VI)/Cr(III) is carried out on the basis of the electrolysis potential (Ee): at pH 4.70 and Ee=−0.30 V, only Cr(VI) is reduced to Cr(III) and accumulated as Cr(OH)3 by adsorption on a mercury film; at Ee=−1.80 V both Cr(VI) and Cr(III) are accumulated forming an amalgam with added mercury(II) ions. Once the film has been formed, the platform is transferred to a graphite tube to atomise the element. The reliability of the method was tested for the speciation of chromium in natural waters and it proves to be highly sensitive thanks to the electroanalytical step. In all samples, the Cr(VI) concentration was less than the detection limit (0.15 ng ml−1), and the concentration of Cr(III) agrees with those of total chromium. The analytical recovery of Cr(VI) added to water samples [3.50 ng ml−1 of Cr(VI)] was 105±6.2%.

Absolute Analysis in Electrothermal Atomic Absorption Spectrometry: PB with Matrix Modifiers

A new method for absolute analysis in Electrothermal Atomization Atomic Absorption Spectroscopy (ETA-AAS), proposed for aqueous solutions, is extended to matrix modifiers based on palladium and magnesium. The experimental results show that only the Pd-based matrix modifier can be accepted for Pb analysis. No differences have been found if tantalum is used instead of graphite as the atomization surface in the same experimental conditions.