Nickel and strontium nitrates as modifiers for the determination of selenium in wine by Zeeman electrothermal atomic absorption spectrometry

A mixed matrix modifier of nickel and strontium nitrates was used as a chemical modifier for the determination of selenium in wines by Zeeman electrothermal atomic absorption spectrometry. Wine samples were heated on a boiling water bath with small amounts of nitric acid and hydrogen peroxide. For complete elimination of interference, especially from sulfates and phosphates, selenium is complexed with ammonium pyrolidinedithiocarbamate (APDTC), extracted into methyl isobutyl ketone (MIBK), and measured by ETAAS. The graphite furnace temperature program was optimized for both aqueous and organic solutions. Pyrolysis temperatures of 1300 degrees C and 800 degrees C were chosen for aqueous and organic solutions, respectively; 2700 degrees C and 2100 degrees C were used as optimum atomization temperatures for aqueous and organic solutions, respectively. The optimum modifier mass established is markedly lower than those presented in the literature. The platform atomization ensures pretreatment stabilization up to 1100 degrees C and 1600 degrees C, respectively, for organic and aqueous selenium solutions. The procedure was verified by the method of standard addition. The investigated wine samples originated from the different regions of the Republic of Macedonia. The selenium concentration varied from not detectable to 0.93 microg L(-1).     

Study of ammonium molybdate to minimize the phosphate interference in the selenium determination by electrothermal atomic absorption spectrometry with deuterium background correction

The use of ammonium molybdate to minimize the phosphate interference when measuring selenium by electrothermal atomic absorption spectrometry (ETAAS) with deuterium background correction was evaluated. Ammonium molybdate did not produce a selenium thermal stabilization; however, the presence of ammonium molybdate decreased the phosphate interference. The study was carried out with mussel acid digests and mussel slurries. Pd–Mg(NO₃)₂ was used as a chemical modifier at optimum concentrations of 300 and 250 mg l⁻¹, respectively, yielding optimum pyrolysis and atomization temperatures of 1200 and 2100 °C, respectively. A yellow solid (ammonium molybdophosphate) was obtained when adding ammonium molybdate to mussel acid digest solutions. This precipitate can be removed after centrifugation prior to ETAAS determination. Additionally, studies on the sampling of the solid ammonium molybdophosphate (AMP) together with the liquid phase, as a slurry, were also developed. The volatilization of the solid AMP was not reached at temperatures lower than 2500 °C. By this way, phosphate, as AMP, is not present in the vapor phase at the atomization temperature (2100 °C), yielding a reduction of the spectral interference by phosphate. The proposed method was validated analyzing three reference materials of marine origin (DORM-1, DOLT-1 and TORT-1). Good agreement with the certified selenium contents was reached for all cases.     

Selenium determination in tissue samples of Nile tilapia using ultrasound-assisted extraction

This paper proposes a method to determine selenium in samples of fish muscle and liver tissue using ultrasound assisted extraction process, and analysed by graphite furnace atomic absorption spectrometry (GFAAS). The selenium content was extracted by 0.10 M HCl at the optimal extraction conditions which were established as follows: sample mass of 100 mg; granulometry of the sample <60 μm; sonication time of five 40 s cycles; and sonication power of 136 W. The selenium determinations were performed by GFAAS, at a drying temperature of 120°C/250°C, pyrolysis temperature of 1300°C, atomization temperature of 2300°C, and cleaning temperature of 2800°C. Palladium nitrate was used as a chemical modifier coinjected with the samples, and tungsten as a permanent modifier. The concentration of selenium determined in the pool of fish muscle and liver tissue were 280.4±4.2 e 592.3±6.7 μg kg⁻¹, respectively. The accuracy and precision of the proposed extraction method were evaluated using certified standard Bovine Muscle — NIST 8414. The results obtained by the ultrasonic extraction method were equivalent to those obtained by the method of acid mineralization of samples in a microwave oven     

Kinetics of selenium atomization in electrothermal atomization atomic absorption spectrometry (ETA-AAS). Part 2: selenium with palladium modifiers

The kinetics of the atomization process of selenium with prereduced and unreduced palladium nitrate modifiers were investigated. It was found that stabilization, in both forms, occurred by principally physical processes, as opposed to compound formation. For the unreduced modifier, it was shown that higher pyrolysis temperatures resulted in a higher activation energy of atomization and that the selenium vapour-surface interaction was increased. The importance of the second high temperature step in the stabilization mechanism was stressed, and an additional conditioning step in the furnace program was proposed for the unreduced palladium modifier. The reaction order for the unreduced modifier was near first order (1.29) with an activation energy of 330 kJ mol⁻¹ and a frequency factor in the order of 1 × 10⁹. For the reduced palladium modifier, a reduction temperature of 500°C–700°C was shown to be most effective. The reduced palladium modifier showed second order kinetics and the activation energy of 500 kJ mol⁻¹, was nearly 50% higher than that of the unreduced form. This and the large frequency factor (ca. 1 × 10¹⁵) indicated strong surface interactions, thus providing an explanation to the better stabilization properties observed for the reduced form of the modifier.     

Liquid-phase microextraction and gas-chromatographic determination of selenium(IV) in aqueous samples

A liquid-phase microextraction (LPME) method was employed for preconcentration of selenium as piazselenol complex in aqueous samples. The samples reacted with o-phenylenediamine in 0.1?M HCl at 90°C for 15?min, and then LPME was performed. A microdrop of carbon tetrachloride was applied as the extracting solvent. After extraction, the microdrop was introduced directly into the injection port of gas chromatography for analysis. Several important extraction parameters such as the type of organic solvent, sample and organic drop volumes, salt concentration, stirring rate, and exposure time were controlled and optimized. In the proposed LPME, the extraction was achieved by suspending a 3?µL carbon tetrachloride drop from the tip of a microsyringe immersed in 12.5?mL of aqueous solution. Under optimized conditions, a dynamic linear range was obtained in the range of 20–1000?µg?L^?1. The preconcentration factor and the limit of detection of selenium in this method were 91 and 0.9?µg?L^?1, respectively. The optimized procedure was successfully applied to the extraction and determination of selenium in different types of real samples. The relative standard deviations for the spiking levels of 50–100?µg?L^?1 in the real samples were in the range of 3.2–6.1%, and the relative errors were located in the range of ?5.4 to 5%.     

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.     

The determination of total Se in urine and serum by graphite furnace atomic absorption spectrometry using Ir as permanent modifier and in situ oxidation for complete trimethylselenonium recovery

The present work evaluated the use of iridium (Ir) as permanent modifier for the determination of total selenium in urine and serum by graphite furnace atomic absorption spectrometry. Concerning urine, the presence of trimethylselenonium (TMSe⁺) was especially considered. Pyrolysis and atomization temperatures of 1,000 and 2,100°C, respectively, were used. For nondigested urine and serum samples, 0.2% v/v HNO₃ and Triton X-100 were used as diluents, respectively, and the same initial platform Ir treatment was effective for up to 1,100 atomization cycles. Good precision [less than 5% relative standard deviation (RSD)] can be achieved with the proposed method. Low TMSe⁺ recovery was observed for nondigested urine samples. Thus, if this species is to be considered in urine analysis, a previous external mineralization step was found to be necessary. Alternatively, an in situ oxidation treatment was developed. Detection limits of 8, 10, and 7 μg l⁻¹ were obtained after dilution, microwave-assisted digestion, and in situ oxidation procedures, respectively. The accuracy of the method was validated by the analysis of certified reference or commercial quality control materials and spiked samples.     

Method development for the determination of thallium in coal using solid sampling graphite furnace atomic absorption spectrometry with continuum source,high-resolution monochromator and CCD array detector

The determination of thallium by graphite furnace atomic absorption spectrometry (GFAAS) is plagued by several difficult-to-control interferences. High-resolution continuum-source GFAAS, a technique not yet commercially available, was used to investigate and eliminate spectral interferences, and to develop a reliable method for the determination of thallium in coal using direct solid sampling. The resolution of 2.1 pm per pixel, and the display of the spectral environment ±0.2 nm on both sides of the analytical line were ideally suited for that purpose. The thallium signal was preceded by excessive non-specific absorption due to the coal matrix when pyrolysis temperatures ≤600 °C were used, and a characteristic molecular absorption with pronounced fine structure was following the atomic absorption. With a pyrolysis temperature of 700 °C the non-specific absorption at the beginning of the atomization stage could be eliminated, and using an atomization temperature of 1700 °C, and no modifier, the atomic absorption could be separated in wavelength and in time from the molecular structures, making possible an interference-free determination of thallium, using Pixel 260 at 276.8085 nm for background correction. The results obtained for 11 coal samples and one coal fly ash were in agreement at a 95% confidence level without a modifier, with palladium added in solution, and with ruthenium as permanent modifier, respectively, using aqueous standards for calibration. A characteristic mass of m₀=12 pg and 5.5 pg was obtained with the center pixel only, and the center pixel ±1, respectively. The precision, expressed as relative standard deviation was typically better than 5%, and the limit of detection, based on three times the standard deviation of the coal with the lowest analyte content, was 0.01 μg g⁻¹.     

Spectrophotometric determination of etodolac in pure form and pharmaceutical formulations

Background

A routine method for the quantification of beryllium in biological fluids is essential for the development of a chelation therapy for Chronic Beryllium Disease (CBD). We describe a procedure for the direct determination of beryllium in undigested micro quantities of human blood and serum using graphite furnace atomic absorption spectrometry. Blood and serum samples are prepared respectively by a simple 8-fold and 5-fold dilution with a Nash Reagent. Three experimental setups are compared: using no modifier, using magnesium nitrate and using palladium/citric acid as chemical modifiers.

Results

In serum, both modifiers did not improve the method sensitivity, the optimal pyrolysis and atomization temperatures are 1000°C and 2900°C, respectively. In blood, 6 μg of magnesium nitrate was found to improve the method sensitivity. The optimal pyrolysis and atomization temperatures were 800°C and 2800°C respectively.

Conclusion

In serum, the method detection limit was 2 ng l^-1, the characteristic mass was 0.22 (± 0.07) pg and the accuracy ranged from 95 to 100%. In blood, the detection limit was 7 ng l^-1, the characteristic mass was 0.20 (± 0.02) pg and the accuracy ranged from 99 to 101%.     

Long term stability of organic selenium species in aqueous solutions

Long term stability of organic selenium compounds (selenocystine, selenomethionine, trimethylselenonium ion) has been studied over a one year period for 2 analyte concentrations: 25 and 150 μg/L Se, at pH 4.5 in the dark, under different storage conditions: temperature of –20°C, 4°C, 20°C, 40°C; in Pyrex, Teflon, or polyethylene containers; in an aqueous matrix or in the presence of a chromatographic counter ion (pentyl sulfonate at 10^–4 mol/L concentration). Light effects have also been tested. The stability of the selenium species was monitored by HPLC-ICP/MS. Storage conditions can drastically alter the stability of organic selenium species. Organoselenium compounds were shown to be stable in the dark over a one year period in an aqueous matrix at pH 4.5 in Pyrex containers at both 4°C and 20°C. Pyrex vials exposed to natural sunlight at room temperature resulted in a steady decrease of the selenoamino acid concentration. Teflon containers caused losses of less than 25% at both 4° C and 20° C in the dark. However, polyethylene vials presented, at all temperatures tested, a rapid decrease of the TMSe⁺ concentration. The stability of the Se species studied did not show significant differences between 4° C and 20° C in any container material used. Storage of solutions at 40° C led to slight differences between the Pyrex and Teflon containers. However, polyethylene presented a drastic decrease of the three species over time at this higher temperature. Solutions frozen at –20° C in polyethylene vials did not stabilize the TMSe⁺ signal. Finally, concentrations and matrices of the samples did not significantly affect the stability of the species. Received: 15 July 1996 / Revised: 14 July 1997 / Accepted: 18 July 1997     

Chromium determination in sea water by electrothermal atomic absorption spectrometry using Zeeman effect background correction and a multi-injection technique

Electrothermal atomic absorption spectrometry (ETAAS) applying a Zeeman effect background correction system (ZEBC) and a tranverse heated atomizer was used to directly determine chromium in sea water. Calcium chloride (at a concentration of 20 mg L^–1) was applied as chemical modifier with optimum charring and atomization temperatures of 1600°C and 2000°C, respectively. The detection limit was 0.2 μg L^–1, by injecting 20 μL aliquot of sea water sample. This detection limit could be reduced further to 0.05 μg L^–1, using multiple injections (injection of five 20 μL aliquot of sea water). The accuracy of the methods developed were confirmed by analyses of different certified reference materials. Finally, interferences from major and minor components of sea water are studied.     

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.     

Direct determination of manganese in produced waters from petroleum exploration by Electrothermal Atomic Absorption Spectrometry using Ir-W as permanent modifier

This present work reports the development and evaluation of a method for the direct determination of manganese in waters extracted during petroleum exploitation by Electrothermal Atomic Absorption Spectrometry (ET AAS) using Ir-W as permanent modifier. These waters, usually called produced waters, contain a wide range of organic and inorganic substances and are characterized by their high salinity. In order to achieve suitable experimental conditions for the method application, studies about the effect of operational variables (chemical modifier, pyrolysis and atomization temperatures) were performed, as well as the establishment of convenient calibration strategy. The best results were verified when the temperatures of pyrolysis and atomization were 1000 °C and 2300 °C, respectively, and using Ir-W as permanent modifier. The results showed that manganese can be determined by the standard addition method or employing external calibration with standard solutions prepared in the same salinity of the samples (with NaCl). Three real samples with salinities varying between 74 and 84‰ were successfully analyzed by the developed procedure. The limits of detection and quantification were 0.24 and 0.80 μg L⁻¹, respectively, in purified water, and 0.34 and 1.1 μg L⁻¹, respectively, in 0.4 mol L⁻¹ NaCl medium (approximately 23‰ salinity).     

Investigation of interferences in the determination of thallium in marine sediment reference materials using high-resolution continuum-source atomic absorption spectrometry and electrothermal atomization

A high-resolution continuum-source atomic absorption spectrometer with a xenon short-arc lamp as the radiation source, a compact double echelle monochromator with a focal length of 302 mm and a spectral resolution of λ/Δλ≈110 000, and a UV-sensitive charged-coupled device (CCD) array detector was used to investigate the spectral interferences found with a conventional line-source atomic absorption spectrometer in the determination of thallium in marine sediment reference materials. A transversely heated graphite furnace was used as the atomizer unit, and the samples were introduced in the form of slurries. A strong iron absorption line at 276.752 nm, which was observed at atomization temperatures >2000 °C in the vicinity of the thallium resonance line at 276.787 nm, could be responsible for some of the interferences observed with low-resolution continuum-source background correction. The outstanding feature at atomization temperatures <2000 °C was the electron excitation spectrum of the gaseous SO₂ molecule that exhibited a pronounced rotational fine structure, and is for sure the main reason for the observed spectral interferences. The molecular structures could be removed completely by subtracting a model spectrum recorded during the atomization of KHSO₄, using a least squares algorithm. The same results, within experimental error, were obtained for thallium in a variety of marine sediment reference materials using ammonium nitrate as a modifier, ruthenium as a permanent modifier in addition to ammonium nitrate, and without a modifier, using aqueous standards for calibration, demonstrating the ruggedness of the method. A characteristic mass of 15–16 pg Tl was obtained, and a limit of detection of 0.02 μg g⁻¹ Tl was calculated from the standard deviation of five repetitive determinations of HISS-1, the sediment with the lowest thallium content.     

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

Gold nanoparticles (AuNPs) were used as a new chemical modifier for the determination of arsenic and antimony in salt solutions by electrothermal atomic absorption spectrometry. The AuNPs were prepared by reducing chloroauric acid with sodium citrate. The effects of pyrolysis and atomization temperatures, the amounts of interferents and modifier on the sensitivities of arsenic and antimony were investigated. As and Sb remain in the graphite tube up to 1,100°C, which is sufficient for the determination of the two metals in certified reference materials and spiked sea water samples within a 95% confidence level with low RSD (<10%). The detection limits (N?=?10 at 3??) for As and Sb in sea water are 2.3???g?L^-1 and 3.0???g?L^-1, respectively. Almost no background as well as a blank value was detected for AuNPs.

Determination of indium in minerals,river sediments and coal fly ash by electrothermal atomic absorption spectrometry with palladium as a matrix modifier

A method is described for the determination of indium (10–40 μg g^?1) in lead-zinc ores and magnetic pyrites. Graphite furnace atomic absorption spectrometry is used with palladium as a matrix modifier. Indium (down to 0.085 μg g^?1) in river sediments and coal fly ash can be determined after pre-extraction with ammonium iodide into 4-methyl-2-pentanone. In the presence of palladium, the maximum tolerable ashing temperatures for indium in aqueous solution or organic extract can be raised to 1200°C or 1000°C, respectively, and the sensitivity is greatly improved.     

Cloud point extraction for the determination of cadmium and lead in biological samples by graphite furnace atomic absorption spectrometry

The phase-separation phenomenon of non-ionic surfactants occurring in aqueous solution was used for the extraction of Cd and Pb from digested biological samples. After complexation with O,O-diethyldithiophosphate (DDTP) in hydrochloric acid medium, the analytes are quantitatively extracted to the phase rich in the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) after centrifugation. Methanol acidified with 0.1 mol L⁻¹ HNO₃ was added to the surfactant-rich phase prior to its analysis by electrothermal atomic absorption spectrometry (ET AAS). The adopted concentrations for DDTP, Triton X-114 and hydrochloric acid were all optimized. Pyrolysis and atomization temperatures were optimized using the extracts and pyrolysis temperatures of 700 °C for both elements and atomization temperatures of 1400 and 1600 °C for cadmium and lead, respectively, were used without adding any modifier, which shows that considerable analyte stabilization is provided by the medium itself. A more detailed investigation was carried out to determine which components of the extract were responsible for the high thermal stability achieved and it revealed that the amount of DDTP added and the phosphorus content of the digested samples contributed significantly to this phenomenon. Detection limits (3σ_B) of 6 and 40 ng g⁻¹, along with enrichment factors of 129 and 18 for Cd and Pb, respectively, were achieved. The proposed procedure was applied to the analysis of five certified biological reference materials after microwave-assisted acid digestion in a mixture of H₂O₂ and HNO₃. Comparison with certified values was performed for accuracy evaluation, resulting in good agreement according to the t-test for a 95% confidence level. The high efficiency of cloud point extraction to carry out the determination of the studied analytes in complex matrices was, therefore, demonstrated.     

Standard Partial Molar Volumes of Aqueous 2- and 3-Hydroxypropionic Acid from 100 to 325 °C: Functional Group Additivity in Isomers with Closely Spaced Polar Groups

Apparent molar volumes have been determined using a high-pressure vibrating-tube densimeter for aqueous solutions of 2- and 3-hydroxypropionic acid, at temperatures from 100?°C to 325?°C and pressures as high as 15 MPa. The results were corrected for acid ionization and extrapolated to infinite dilution to obtain the standard partial molar volumes, V ₂ ^o . The standard partial molar volumes of both isomers increase with temperature towards a positive discontinuity at the critical point, which is typical for almost all non-electrolytes. The temperature dependence of V ₂ ^o for the sodium salts of the acids is consistent with a negative discontinuity at the critical point, as displayed by all other aqueous electrolytes. Values of the apparent molar volumes of 2-hydroxypropionic acid are more positive than 3-hydroxypropionic acid by ～2 cm³?mol^?1, both in the neutral form and as the sodium carboxylate salt. This is the first demonstration at such high temperatures that functional group additivity in alkyl organic solutes with closely spaced polar groups is preserved to within such small differences. The onset of thermal decomposition prevented measurements at temperatures above 325?°C.     

Simple Method for Determination of Lead in Hair Dyes Using Slurry Sampling Graphite Furnace Atomic Absorption Spectrometry

A fast, simple and sensitive method for determining of lead in hair dyes using graphite furnace atomic absorption spectrometry with slurry sampling was developed. Multivariate optimization was used to establish optimal analytical parameters through a fractional factorial and a central composite design. The samples were submitted for direct analysis without prior digestion and were diluted in 2.5% v/v HNO₃ and 1.5% v/v H₂O₂. Palladium (chemical modifier) and rhodium (permanent modifier) were selected from several potential modifiers. The optimal conditions were a pyrolysis time of 10 s (liquid and dust dyes) 20 s (cream dyes), a pyrolysis temperature of 789°C (liquid dyes) or 750°C (cream and dust dyes) and an atomization temperature of 1800°C for all dyes. Under optimum conditions, the calibration graph is linear in the 1.50–50.0 µg L^?1 concentration range, with a detection limit of 0.33, 0.44, and 0.39 µg L^?1 for liquid, dust, and cream hair dyes, respectively. The relative standard deviation ranged from 1.63 to 4.56%. The recovery rate ranged from 85 to 108%, and no significant differences were found between the results obtained with the proposed method and the microwave decomposition analysis method of real samples. The concentration ranges obtained for lead in the hair dyes samples were 1.00–11.3 µg L^?1 for liquid dyes, 14.0–100 µg kg^?1 for dust dyes, and 19.9–187 µg kg^?1 for cream dyes.     

Comparison of two digestion procedures for the determination of lead in lichens by electrothermal atomic absorption spectrometry

The efficiency of two procedures for the digestion of lichen was investigated using a heating block and a microwave oven. In the open vessels, concentrated nitric acid was added to the samples, left for 1 h, and the addition of 30% (v / v) hydrogen peroxide completed the digestion. In the closed system, the complete digestion was performed using concentrated nitric acid and hydrogen peroxide, reducing the amount of chemicals, time and contamination risk. Both digestion methods gave comparable results, and recoveries were statistically not different. For a lichen sample spiked with 10 μg Pb, the recovery was 111% and 110% using microwave and heating block digestion, respectively, while it was 100% and 103% for a 100 μg Pb spike. For the determination by electrothermal atomic absorption spectrometry samples were diluted 20 times with water and a volume of 20 μL was injected into the graphite furnace without chemical modifier. Pyrolysis and atomization temperatures of 700 °C and 1500 °C, respectively, were used. The characteristic mass was 8.4 ± 0.6 pg for aqueous calibration solutions and 8.9 ± 0.8 pg for samples. Calibration was against matrix matched standards. The recovery test showed some contamination problem with the lowest concentrations in both procedures. The detection limits were 4.4 μg L^− 1 with microwave oven and 5.4 μg L^− 1 with the heating block in the undiluted blank.