Discussion of parameters associated with the determination of arsenic by electrothermal atomic absorption spectrometry in slurried environmental samples

A slurry sampling – fast program procedure has been developed for the determination of arsenic in plants, soils and sediments by electrothermal atomic absorption spectrometry. Efficiencies of various single and mixed modifiers for thermal stabilization of arsenic and for a better removal of the matrix during pyrolysis step were compared. The influence of the slurry concentration, amounts of modifier and parameters of the pyrolysis step on the As integrated absorbance signals have been studied and a comparison between fast and conventional furnace programs was also made. The ultrasonic agitation of the slurry followed by a fast electrothermal program using an Ir/Mg modifier provides the most consistent performance in terms of precision and accuracy. The reliability of the whole procedure has been compared with results obtained after application of a wet digestion method with an HF step and validated by analyzing eleven certified reference materials. Arsenic detection and quantitation limits expressed on dry sample matter were about 30 and 100 μg kg^–1, respectively.     

Slurry sampling techniques for the determination of lead in Bangladeshi fish samples by electrothermal atomic absorption spectrometry with a metal tube atomizer

Ultrasonic slurry sampling electrothermal atomic absorption spectrometry with a metal tube atomizer has been applied to the determination of lead in Bangladeshi fish samples. The slurry sampling conditions, such as slurry stabilizing agent, slurry concentration, pyrolysis temperature for the slurried fish samples, particle size and ultrasonic agitation time, were optimized for electrothermal atomic absorption spectrometry with the Mo tube atomizer. Thiourea was used as the chemical modifier for the interference of matrix elements. The detection limit was 53 fg (3S/N). The determined amount of lead in Bangladeshi fish samples was consistent with those measured in the dissolved acid-digested samples. The advantages of the proposed methods are easy calibration, simplicity, low cost and rapid analysis.     

Evaluation of pyrolysis curves for volatile elements in aqueous standards and carbon-containing matrices in electrothermal vaporization inductively coupled plasma mass spectrometry

Pyrolysis curves in electrothermal atomic absorption spectrometry (ET AAS) and electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) have been compared for As, Se and Pb in lobster hepatopancreas certified reference material using Pd/Mg as the modifier. The ET AAS pyrolysis curves confirm that the analytes are not lost from the graphite furnace up to a pyrolysis temperature of 800 °C. Nevertheless, a downward slope of the pyrolysis curve was observed for these elements in the biological material using ETV-ICP-MS. This could be related to a gain of sensitivity at low pyrolysis temperatures due to the matrix, which can act as carrier and/or promote changes in the plasma ionization equilibrium. Experiments with the addition of ascorbic acid to the aqueous standards confirmed that the higher intensities obtained in ETV-ICP-MS are related to the presence of organic compounds in the slurry. Pyrolysis curves for As, Se and Pb in coal and coal fly ash were also investigated using the same Pd/Mg modifier. Carbon intensities were measured in all samples using different pyrolysis temperatures. It was observed that pyrolysis curves for the three analytes in all slurry samples were similar to the corresponding graphs that show the carbon intensity for the same slurries for pyrolysis temperatures from 200 °C up to 1000 °C.     

Determination of Antimony in Sediments by Zeeman-Corrected Electrothermal Atomic Absorption Spectrometry with Ultrasonic Slurry Sampling

A method was developed for the determination of antimony in slurried sediments (on the basis of samples of three Certified Reference Materials) by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman-effect background correction. Slurried samples were prepared in 6% nitric acid containing 0.02% of Triton X-100. A mixed palladium/magnesium chemical matrix modifier, L'vov platform atomization and a temperature-time program with a relatively short (10 s) sample pyrolysis stage were used. The results of the determinations by this technique are in very close agreement with certified values and the repeatability of this analytical procedure expressed in terms of relative standard deviation was typically better than 9% at the slurry concentration of approx. 90 mg/2 mL. The characteristic mass of Sb (at the spectral line 231.1 nm) was 25.6 pg and the limit of detection (calculated for 100 mg/2 mL slurry) was about 0. 04 μg/g.     

Direct Determination of Arsenic in Beet Sugar Molasses Using Nickel as Chemical Modifier by Electrothermal Atomic Absorption Spectrommetry

A simple electrothermal atomic absorption spectrometric (ETAAS) method is described for direct determination of arsenic in sugar beet molasses samples. Pyrolytic graphite tubes were used as atomizers. The compression between modifiers such as nickel nitrate, palladium nitrate and the mixture of palladium and magnesium nitrate were performed and nickel nitrate selected as the best chemical modifier. The effects of pyrolysis and atomization temperature were also studied and the pyrolysis temperature of 900 °C and atomization temperature of 2300 °C have been chosen for temperature program. The detection limit of the method was 1 ng/mL As in sugar beet molasses samples. The relative standard deviation for ten determination of a spiked sample with concentration of 50 ng/mL As was 2.4%. The accuracy of the method was confirmed by the analysis of spiked samples. The linear rang of calibration is in the range of 1‐100 ng/mL of arsenic.     

Electrothermal atomization of arsenic,antimony and thallium using a graphite atomizer with refractory metal platforms

The electrothermal atomization of the volatile elements arsenic, antimony and thallium from a refractory metal platform consisting of a tungsten coil and/or a refractory metal foil with the dimensions of a conventional graphite platform was studied. Several combinations of refractory metal platforms were investigated, as follows: W platform; Ta platform; W coil; W coil on a W platform and W coil on a Ta platform. The best combination for these elements as regards both thermal stabilization and sensitivity is the W coil on a Ta platform. Thermal stabilization is also achieved with a W coil on a W platform. The presence of Pd-containing chemical modifier favors the thermal stabilization of the analytes. The sufficient amount is 2 micrograms of Pd. The maximal temperatures of pyrolysis are higher (arsenic, antimony) or equal (thallium) to those when using different chemical modifiers, added as solutions. It may be concluded, that the refractory metal platforms act as "built-in modifiers". They are suitable for the determination of arsenic, antimony and thallium in samples of complex matrix composition where high thermal stability of the analytes during the pyrolysis step is required.     

Determination of tellurium in indium antimonide semiconductor material by electrothermal atomic absorption spectrometry

A method for the determination of the dopant concentration of tellurium in dissolved indium antimonide semiconductor material by electrothermal atomic absorption spectrometry (ETAAS) was developed. Efforts were made to investigate the optimal conditions of the furnace heating program and the effect of palladium modifier on the variation of tellurium and the background absorbance. According to the results obtained, the presence of palladium chemical modifier in the analysis of indium antimonide allowed the successful retention of tellurium in the graphite tube, and the optimum mass of palladium modifier was found to be dependent on the sample matrix concentration. The absorbance profile of tellurium and the background level were significantly improved when a pyrolysis temperature of 1100 degrees C and an atomization temperature of 2200 degrees C were employed in the optimized heating program. With the use of this method, a detection limit of 0.8 microg g(-1) tellurium in indium antimonide could be achieved. The applicability of the proposed method was evaluated by comparison with two independent methods, i.e. slurry sampling-ETAAS and ICP-MS. From the good agreement between the results, it was demonstrated that the proposed method is suitable for the determination of typical dopant concentrations of tellurium in indium antimonide.     

The use of silver nanoparticles as an effective modifier for the determination of arsenic and antimony by electrothermal atomic absorption spectrometry

Silver nanoparticles (AgNPs) were proposed as a new chemical modifier for the elimination of interferences when determining arsenic and antimony in aqueous NaCl or Na₂SO₄ solutions and in sea-water by electrothermal atomic absorption spectrometry. For this purpose, the AgNPs were prepared simply by reducing silver nitrate with sodium citrate. The effects of pyrolysis and atomization temperatures and the amounts of interferents and modifiers on the sensitivities of these elements were investigated. In the presence of the proposed modifier, a pyrolysis temperature of at least 1100 °C for arsenic and 900 °C for antimony could be applied without the loss of analytes, and the interferences were greatly reduced to allow for interference-free determination. The detection limits (N = 10, 3σ) for arsenic and antimony were 0.022 ng and 0.046 ng, respectively. AgNPs are cheaper and more available compared to many other modifiers. No background was detected, and the blank values were negligible.     

Slurry sampling electrothermal atomic absorption spectrometric determination of copper in herbal medicine samples with a molybdenum tube atomizer

An ultrasonic slurry sampling electrothermal atomic absorption spectrometric method with a molybdenum tube atomizer has been developed for the determination of copper in herbal medicine samples. Glycerol solution (10%) was used as the slurry medium. The optimum pyrolysis temperature was 760 °C. The detection limit was 72 fg (3×S/N ratio). Matrix element interference was investigated and it was found that glycerol as a chemical modifier eliminated the interference. The amounts of copper in herbal medicines determined by the method proposed are in good accordance with those measured in dissolved acid-digested samples. The method enables rapid calibration, and simple and rapid analysis of copper in herbal medicine samples at low cost.     

Investigation of interference mechanism of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry

The interferences of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry (ETAAS) were examined using a dual cavity platform (DCP), which allows the gas-phase and condensed phase interferences to be distinguished. Effects of pyrolysis temperature, pyrolysis time, atomization temperature, heating rate in the atomization step, gas-flow rate in the pyrolysis and atomization steps, interferent mass and atomization from wall on sensitivity as well as atomization signals were studied to explain the interference mechanisms. The mechanism proposed for each experiment was verified with other subsequent sets of experiments. Finally, modifiers pipetted on the thermally treated sample+interferent mixture and pyrolyzed at different temperatures provided very useful information for the existence of volatilization losses of analyte before the atomization step. All experiments confirmed that when low pyrolysis temperatures are applied, the main interference mechanisms are the gas-phase reaction between bismuth and decomposition products of cobalt chloride in the atomization step. On the other hand, at elevated temperatures, the removal of a volatile compound formed between analyte and matrix constituents is responsible for some temperature-dependent interferences, although gas-phase interferences still continue. The experiments performed with colloidal palladium and nickel nitrate showed that the modifier behaves as both a matrix modifier and analyte modifier, possibly delaying the vaporization of either analyte or modifier or both of them.     

Low-temperature migration of lead,thallium, and selenium onto a palladium modifier during the analysis of solutions and slurries by electrothermal atomic absorption spectrometry

A palladium/magnesium modifier, when premixed with solutions or slurries, stabilizes many analytes to higher pyrolysis and atomization temperatures. Similar behavior was seen when analyte and modifier were physically separated by pipetting them onto opposite sides of a L'vov platform. During the pyrolysis stage of the furnace heating cycle, lead, thallium, and selenium migrated from the platform surface and interacted with the modifier on the opposite side. This behavior explains the consistent stabilization by palladium of analytes in slurry samples. Under conventional operating conditions the modifier is premixed with the slurry, and on drying in the furnace, the analyte and modifier may not make close contact. However, this is unimportant since the analyte will migrate to the palladium on heating. Then the rate-limiting step leading to atomization is the release of analyte from palladium, and it is the same for solutions and slurries. Therefore, aqueous standards can be used for slurry analysis.     

Determination of Bismuth in Sediment and Soil by Ultrasonic Slurry Sampling Electrothermal Atomic Absorption Spectrometry

The analytical conditions of the direct determination of bismuth in some certified reference material samples (soil and sediment) by slurry sampling Zeeman electrothermal atomic absorption spectrometry (ETAAS) with the use of automated ultrasonic slurry mixing are discussed. Palladium nitrate was used as a chemical modifier. With the use of this modifier it was possible to stabilize bismuth to the pyrolysis temperature of 1300 °C. Platform atomization was performed at 2050 °C. The results of determination are calculated from a simple, aqueous standards based calibration graph. Statistical evaluation of the results indicate that the slurry sampling method is reproducible and the accuracy of the proposed method is very good. This method is rather simple and its other advantages are good sensitivity and relatively short analysis time.     

Determination of lead in fine particulates by slurry sampling electrothermal atomic absorption spectrometry

A simple method for determining lead in fine particulates (PM2.5) by using electrothermal atomic absorption spectrometry (ETAAS) has been developed. Particulates collected on Nuclepore filter by using a dichotomous sampler were suspended in diluted nitric acid after ultrasonic agitation. The dislodging efficiency is nearly 100% after agitation for 5 min. In order to study the suspension behavior of PM2.5 in solvents, a Brookhaven ZetaPlus Particle Size Analyzer was used to determine the particle size distribution and suspension behavior of air particulates in the solvent. The pre-digestion and modification effect of nitric acid would be discussed. Palladium was added as a chemical modifier and the temperature program of ETAAS was changed in order to improve the recovery. The slurry was introduced directly into a graphite tube for atomization. The metal content in the sample was determined by the standard addition method. In addition, a conventional acid digestion procedure was applied to verify the efficiency of the slurry sampling method. It offers a quick and efficient alternative method for heavy metal characterization in fine particulates.     

Vaporization of Pb,As and Ga alone and in the presence of Pd modifier studied by electrothermal vaporization-inductively coupled mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) with electrothermal vaporization (ETV) was used to study the processes taking place in a graphite furnace for atomic spectroscopy. Monitoring of carbon release during the pyrolysis stage provided information on the solid-state reduction processes. Among three carbon species studied (¹²C, ¹³C and ²⁸CO), ¹³C was found to be the most suitable. Gallium and arsenic oxides practically do not reduce during the pyrolysis stage. According to the data on carbon release, two reduction processes of lead species (at about 690–915 and > 1000 °C) were found to take place in the furnace. Two separate peaks of Pb (at the end of the pyrolysis stage and in the vaporization stage) were observed, probably related to vaporization of unreduced lead oxide and elemental Pb, respectively. A pre-reduced palladium modifier suppresses the low-temperature Pb losses so that the high-temperature Pb peak is increased. In the absence of modifier, a gaussian-shaped As signal was formed only if small arsenic masses were introduced into the vaporizer. Increase of the arsenic mass resulted in formation of a pronounced plateau after the peak, in spite of the very high vaporization temperature applied (2500 °C). In the presence of pre-reduced palladium modifier, a gaussian-shaped As signal was formed already at 1700 °C with a 4–15-fold increase in sensitivity depending on the analyte mass. The palladium modifier apparently prevents strong interaction of arsenic with graphite. The obtained data support very high potential of ETV-ICP-MS for detailed investigation of processes occurring in graphite furnaces used in analytical atomic spectroscopy, especially during the pyrolysis stage.     

Determination of manganese in brain samples by slurry sampling graphite furnace atomic absorption spectrometry

A simple procedure for the determination of manganese in different sections of human brain samples by graphite furnace atomic absorption spectrometry has been developed. Brain sections included cerebellum, hypothalamus, frontal cortex, vermix and encephalic trunk. Two sample preparation procedures were evaluated, namely, slurry sampling and microwave-assisted acid digestion. Brain slurries (2% w/v) could be prepared in distilled, de-ionized water, with good stability for up to 30 min. Brain samples were also digested in a domestic microwave oven using 5 ml of concentrated HNO₃. A mixed palladium+magnesium nitrate chemical modifier was used for thermal stabilization of the analyte in the electrothermal atomizer up to pyrolysis temperatures of 1300 °C, irrespective of the matrix. Quantitation of manganese was conducted in both cases by means of aqueous standards calibration. The detection limits were 0.3 and 0.4 ng ml⁻¹ for the slurry and the digested samples, respectively. The accuracy of the procedure was checked by comparing the results obtained in the analysis of slurries and digested brain samples, and by analysis of the NIST Bovine Liver standard reference material (SRM 1577a). The ease of slurry preparation, together with the conventional set of analytical and instrumental conditions selected for the determination of manganese make such methodology suitable for routine clinical applications.     

Determination of manganese in herbal medicine samples by slurry-sampling electrothermal atomic absorption spectrometry with a metal tube atomizer

An ultrasonic slurry-sampling electrothermal atomic absorption spectrometry with a molybdenum tube atomizer has been developed for the determination of manganese in herbal medicine samples. Ten percent glycerol solution was used as the slurry medium. The optimum pyrolysis temperature was 400 degrees C. The detection limit was 69 fg (3xS/N). Matrix element interference was checked and it was found that glycerol as a chemical modifier eliminated the interference. The amounts of manganese in herbal medicines determined by the proposed method are in good accordance with those measured in dissolved acid-digested samples. The method enables rapid calibration, and simple and rapid analysis of manganese in herbal medicine samples at low cost.     

Electrothermal atomic absorption spectrometric determination of cadmium in bangladeshi vegetables with a metal tube atomizer and slurry sampling technique

Ultrasonic slurry sampling electrothermal atomic absorption spectrometry with a molybdenum tube atomizer has been applied for the determination of cadmium in vegetable samples in Bangladesh. The suspension-stabilizing medium was 10% glycerol solution. The optimum pyrolysis temperature was 300°C. The detection limit was 13?fg (3S/N). Matrix element interference was studied and it was found that thiourea as a chemical modifier eliminated the interference. The results for the determination of cadmium in vegetable samples by the proposed method were in good agreement with those measured in dissolved acid-digested samples. The method enables rapid calibration, and simple and rapid analysis of cadmium in vegetable samples at low cost.     

Heated Slurry Sampling for the Determination of Cadmium in Food by Electrothermal Atomic Absorption Spectrometry

A heating procedure is reported with slurry sampling electrothermal atomic absorption spectrometry to improve the accuracy of cadmium determination in food. In comparison to conventional slurry sampling, the heating significantly increased cadmium recovery and improved the precision. For the optimized procedure, 25–250 mg of food were treated with 2% HNO₃ and 1% H₂O₂ with heating at 120°C for 20 min, followed by the addition of 50 µL of 10% Triton X-100, and homogenization in an ultrasonic bath prior to analysis. Tungsten and rhodium were employed as a permanent modifier with optimum pyrolysis and atomization temperatures of 500°C and 1500°C. Calibration with aqueous standards resulted in good agreement between certified or information values and measured results at the 95% confidence level. A characteristic mass of 0.8 ± 0.1 pg and a detection limit of 0.7 ng g^?1 for a 2% slurry were obtained. The method was employed for the direct determination of cadmium in food certified reference materials.     

Simultaneous determination of lead, nickel, tin and copper in aluminium-base alloys using slurry sampling by electrical discharge and multielement ETAAS

The simultaneous multielement determination of Pb, Sn, Ni and Cu in aluminium alloys by electrothermal atomic absorption spectrometry (ETAAS) was performed by a quick method using slurry sampling. The metallic colloidal slurries were obtained by an electrical discharge operated in liquid medium. In this work, the effects of aluminium were evaluated and the results show that it causes a strong retention of Pb, Ni and Cu at low pyrolysis temperatures which is overcome by employing high pyrolysis temperatures. Aluminium also significantly improves the thermal stabilisation of Pb and Sn, it being possible to reach pyrolysis temperatures of 1100 and 1300 °C, respectively. Such stabilisation indicates that the performance of aluminium as a matrix modifier for Pb is better than that obtained using phosphate and magnesium nitrate without substantial changes of the figures of merit. The effects of aluminium on the atomisation characteristics of the elements and those coming from the simultaneous multielement determination on the figures of merit of the elements are also discussed. In this work, a calibration procedure involving a matrix matching method with aqueous aluminium standards is proposed as a simple and efficient way to solve the inconveniences originated by the aluminium matrix. The proposed method was applied to the simultaneous multielement determination of several aluminium-base alloy standards giving results well within the recommended values.     

Chemical Modifiers Based on Platinum-Group Metal Compounds in Electrothermal Atomic Absorption Spectrometry

Mechanisms of the action of chemical modifiers based on platinum-group metals have been considered. It has been shown that the efficiency of a chemical modifier is determined mainly by chemical processes occurring at the pyrolysis step. By combining the results obtained using different methods, these processes have been described step-by-step. The systematic study of Pd, Pt, Rh, Ru, and Ir in chloride and sulfate media as chemical modifiers has revealed a correlation between the relative efficiencies and some chemical properties of the modifiers. It has been shown that, in the presence of matrices weakly interacting with platinum-group metals (for example, sodium chloride), the best modifiers are metals that most intensely interact with the analytes (ruthenium and iridium in determining metalloids). However, if the chemical modifier strongly interacts with the sample matrix, the efficiency of the modifier is determined by the interaction processes. For example, in the presence of a sulfate matrix capable of reacting with platinum-group metals, the best modifier is palladium. The correlations found may be useful for the practical application of platinum-group metals as chemical modifiers in the analysis of complex samples by electrothermal atomic absorption spectrometry.