Direct and simultaneous determination of copper and manganese in seawater with a multielement graphite furnace atomic absorption spectrometer

The direct and simultaneous determinations of Cu and Mn in seawater using a multielement graphite furnace atomic absorption spectrometer (Perkin-Elmer SIMAA6000) are described. Three kinds of chemical modifier (Mg(NO₃)₂, Pd(NO₃)₂ and a mixture of these) were tested. The matrix interferences were removed completely so that a simple calibration curve method could be used to determine Cu and Mn in seawater from the open ocean using Pd or a mixture of Pd and Mg as the chemical modifier. The relative standard deviations (RSDs) for the simultaneous determination of Cu and Mn in seawater from open ocean are 10% or less, and the detection limits were 0.07 μg 1⁻¹ for Cu and 0.10 μg 1⁻¹ for Mn, using Pd as the chemical modifier. The accuracy of the method is confirmed by analysis of four kinds of certified reference saline waters.     

Evaluation of electrodeposited tungsten chemical modifier for direct determination of chromium in urine by ETAAS

The direct determination of chromium in urine by electrothermal atomic absorption spectrometry (ETAAS) using graphite tubes modified with tungsten is proposed. Modification of the graphite is made by tungsten electrodeposition over the whole surface atomizer followed by carbide formation by heating the tube inside its own furnace. For tungsten electrocoating, the graphite tube and a platinum electrode were connected to a power supply as cathode and anode, respectively, and immersed in a solution containing 2 mg of W in 0.1% v/v HNO₃. Then, 5 V was applied between the electrodes during 20 min for tungsten electrodeposition over the whole atomizer. A SpectrAA 220 Varian atomic absorption spectrometer equipped with a deuterium background corrector was used throughout. Undiluted urine (20 μl) was delivered over the tungsten-treated tube and the chromium-integrated absorbance was measured after applying a suitable heating program with maximum pyrolysis at 1300 °C and atomization at 2500 °C. With electrodeposited tungsten modifier, the tube lifetime increased up to four times when compared to previous published methods for Cr determination in urine by ETAAS, reaching 800 firings. Method detection limit (3 S.D.) was 0.10 μg l⁻¹, based on 10 integrated absorbance measurements of a urine sample with low Cr concentration. Two reference materials of urines (SRM 2670) from National Institute of Standards and Technology (NIST) were analyzed for method validation. For additional validation, results obtained from eight human urine samples were also analyzed in a spectrometer with Zeeman effect background correction.     

Calibration possibilities and modifier use in ETV ICP OES determination of trace and minor elements in plant materials

The possibilities for universal calibration based on multi-element aqueous standard solutions and graphite laboratory reference materials (graphite standards) for the electrothermal vaporization inductively coupled plasma optical emission spectrometric (ETV ICP OES) determination of Al, B, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, P, Pb, S, Sr, Ti, V, and Zn in plant materials were investigated. A commercially available state-of-the-art ETV device was coupled with an Echelle ICP spectrometer equipped with a charge-injection-device (CID) camera for spectral detection. The transition area between transport tube and ETV graphite tube and the gas streams for inner gas, bypass gas, and modifier gas were optimized to achieve best transport efficiencies. The influence of four gaseous modifiers (CCl₄, CHCl₃, CCl₂F₂, and C₃H₈) added to the inner gas was studied. Five reference materials (RM P-Alfalfa, Lucerne; NIES CRM No.9 “Sargasso”; CTA-VTL-2 Virginia Tobacco Leaves; NIST SRM 1515 Apple Leaves; IAEA-V-10 Hay Powder) were used for method validation. If certified reference materials are not available, calibration against graphite standards or dried aqueous standard solutions is possible. Three carbonization procedures as sample pretreatment for the plant materials were investigated. Figure Picture of the ETV system (sample changer and graphite-tube furbace) used in this work Presented at the European Symposium on Atomic Spectrometry (ESAS) September 28-October 1, 2008, Weimar, Germany.     

The selection of a chemical modifier for vanadium determination in various types of natural waters by electrothermal atomic absorption spectrometry

Various modifiers (ascorbic acid, NH₄NO₃, EDTA, NH₄SCN and a mixture of Pd/Mg(NO₃)₂) are compared for the accurate determination of vanadium in natural waters by electrothermal atomic absorption spectrometry. The interferences of compounds commonly present in natural waters, such as NaCl, CaCl₂, MgCl₂ and FeCl₃ are studied. Matrix interferences were effectively eliminated by ascorbic acid or ammonium nitrate. For comparison, the standard addition method was applied without a modifier which provided satisfactory results. The accuracy of the method was confirmed by analysis of certified reference materials of waters (‘Trace Metals in Drinking Water’ and SRM 1643e ‘Trace Elements in Water’) as well as by recoveries of vanadium spiked to tap water, mineral water, synthetic riverine and synthetic sea waters. The limits of detection and characteristic masses for ascorbic acid and ammonium nitrate as the modifiers were 1.71 and 1.56?µg?L^?1 and 70 and 67?pg, respectively. Recovery was in the range of 98–105% and RSD was less than 5%.     

Sub-Microdetermination of Antimony (Iii) and Antimony (V) In Natural and Polluted Waters and Total Antimony In Biological Materials By Flameless Aas Following Extractive Separation With N-P-Methoxyphenyl-2-Furylacrylohydroxamic Acid

Abstract

Antimony (III) was separated from antimony (V) by extractive separation from 2–10^?6 M HC1 media with N-p-methoxyphenyl-2-furylacrylohydroxamic acid (MFHA) in chloroform and determined by graphite furnace atomic absorption spectroscopy at 2600°C using copper as matrix modifier. Antimony (V) was subsequently reduced to the trivalent form with acidic (-1M HC1) potassium iodide solution and determined as above. the mutual tolerance between antimony (III) and antimony (V) in the present mothod was very high-either of the species could be determined in presence of 15 times higher concentration of the other species. the sepatation-AAS determination system enabled accurate differential analysis of the metalloid in natural/ polluted waters down to 10^?2 ppb (ug 1^?1) levels. the method was also applied to the analysis of antimony in vehicle exhaust particulates, plant tissues, and animal tissues. the method was validated by analysing several certified reference materials with and without standard addition of antimony. MFHA was chosen from amongst thirteen new hydroxamic acids.     

Determination of traces of Ni in Li(2)CO(3)/Na(2)CO(3) melts by graphite furnace atomic absorption spectrometry

A graphite furnace atomic absorption method is described for the determination of traces of Ni in 52 mole percent (mol.%) Li₂CO₃ and 48 mol.% Na₂CO₃ melts after dissolution of the sample in dilute nitric acid. Maximum pyrolysis and optimum atomisation temperatures for the analyte were determined in the presence of the Li and Na matrix constituents. Pre-pyrolysed ascorbic acid (typical amount of 5 μg) has been used as chemical modifier for effectively suppressing the chemical and spectral interferences of the Li/Na matrix, thus that the analysis can be conducted using acid-matched standard solutions. The results of the Ni analysis in synthetic sample solutions by calibration graph against acid-matched standards well agree with those obtained by the method of standard additions. Recoveries ranged from 99 to 101% and the relative standard deviation is around 3% at the 20 μg L⁻¹ level. Moreover, the use of the chemical modifier leads to an improvement of the lifetime of the graphite tube. The Ni detection limit (3σ) in Li/Na carbonate melts for the proposed method is similar to that obtained in aqueous solution, i.e. 5 × 10⁻⁸ g analyte per gram of (Li_0.52Na_0.48) ₂CO₃ melt. This method is successfully applied to the determination of nickel in real carbonate melt samples.     

Cadmium Determination in Human Whole Blood by Electrothermal Atomic Absorption Spectrometry with Magnesium Chloride and Sodium Hydroxide as a Combined Chemical Modifier

In this work, we propose a method to determine trace amounts of Cd in human whole blood samples by electrothermal atomic absorption spectrometry (ETAAS) with the combined chemical modifier including magnesium chloride and sodium hydroxide. Prior to the ETAAS analysis, dissolution of the blood samples is accomplished using a HNO₃-HClO₄double closed-vessel microwave digestion technique followed by drying of the dissolved blood samples by means of an infrared lamp. In using this approach, a MgCl₂ chemical modifier is added to the digested samples, then they are injected into the graphite furnace for detecting the Cd level via atomic absorption spectrometer. Besides we used a NaOH chemical modifier, which removed the matrix major elements through prior ashing at 1200 ° C for 30 s, and the Cd is subsequently volatilized at 2200 °C and determined by AAS. However, the proposed method can be employed to determine the of Cd level in whole blood samples by the calibration technique and the standard-additions method. Its validity is confirmed with two certified reference whole blood materials (Seronorm Trace Elements Whole Blood Batch no. 205052 and Batch no. 203056). By using 10 μL injections, a detection limit of 0.052 ng mL^?1 is achieved.     

Feasibility of eliminating interferences in graphite furnace atomic absorption spectrometry using analyte transfer to the permanently modified graphite tube surface

A procedure is proposed to avoid spectral and/or non-spectral interferences in graphite furnace atomic absorption spectrometry (GF AAS) by transferring the analyte during the pyrolysis stage from a solid sampling platform to the graphite tube wall that has been coated with a permanent modifier, e.g. by electrodeposition of a platinum-group metal. The direct determination of mercury in solid coal samples was chosen as a model to investigate the feasibility of this idea. The graphite tube surface was coated with palladium and the analyte was transferred from the solid sampling platform to the tube wall at a temperature of 500±50 °C. A characteristic mass of m₀=64 pg Hg was obtained for an atomization temperature of 1300 °C, proposing a quantitative transfer of the analyte to the tube wall. Calibration against aqueous mercury standards was not feasible as this element was lost in part already during the drying stage and could not be trapped quantitatively on the modified graphite tube surface. However, the results for all except one of the coal reference materials were within the 95% confidence interval of the certificate when the slope of a correlation curve between the integrated absorbance, normalized for 1 mg of sample, and the certified value for mercury was used for calibration. A detection limit of 0.025–0.05 μg g⁻¹ Hg in coal, calculated from three times the standard deviation of the investigated coal samples, could be obtained with the proposed method. The spectral interference due to excessive background absorption in the direct determination of mercury in coal could be eliminated completely. It is expected that this analyte transfer can be used in a similar way to eliminate other spectral and/or non-spectral interferences in the GF AAS determination of other volatile analytes.     

Determination of lead in waters and sediments from the wetland Tablas de Daimiel National Park (Spain)

Electrothermal atomic absorption spectrometry (ETAAS) has been used for lead control in waters and sediments of the wetland Tablas de Daimiel National Park. The lead determination in the wetland water is hindered by an enhanced salt content, so matrix interference was evaluated. The use of stabilized temperature platform atomization technique, Zeeman background correction and palladium nitrate as matrix modifier were found advisable. For the sediments a closed-vessel microwave dissolution method has been proposed using a mixture of HCl-HNO₃-HF and a heating time of 90 s. With subsequent ETAAS using platform atomization and Zeeman background correction, no chemical modification was necessary. Using these conditions, the interferences were completely removed for both waters and sediments and the calibration curve in ultrapure water (1% nitric acid) was linear up to 30 μg/L. The detection limits for waters and sediments were 0.95 μg/L and 0.78 μg/g, respectively. The accuracy of the proposed method for sediments was validated by analyzing certified reference materials (obtained values were within the certified ones) and spiked wetland sediments (mean recovery of 99.0%). Received: 11 October 1998 / Revised: 3 December 1998 / Accepted: 11 March 1999     

Determination of inorganic tin and organotin compounds by graphite-furnace atomic absorption spectrometry with a new matrix modifier

The determination of total tin in water samples by graphite-furnace atomic absorption spectrometry is described. A matrix modifier containing 0.4% (w/v) potassium dichromate and 0.2% ammonium dihydrogenphosphate in 2% nitric acid is proposed. Interferences from major ions in natural fresh waters decreased and the sensitivity is greatly improved. The procedure is compatible with all the commercial injection devices and requires no pretreatment of the graphite furnace or use of a stabilized temperature platform. The 3σ detection limit is 0.62 ng Sn ml^?1, and calibration is linear up to 30 ng ml^?1 tin.     

Determination of lead in waters and sediments from the wetland Tablas de Daimiel National Park (Spain)

Electrothermal atomic absorption spectrometry (ETAAS) has been used for lead control in waters and sediments of the wetland Tablas de Daimiel National Park. The lead determination in the wetland water is hindered by an enhanced salt content, so matrix interference was evaluated. The use of stabilized temperature platform atomization technique, Zeeman background correction and palladium nitrate as matrix modifier were found advisable. For the sediments a closed-vessel microwave dissolution method has been proposed using a mixture of HCl-HNO₃-HF and a heating time of 90 s. With subsequent ETAAS using platform atomization and Zeeman background correction, no chemical modification was necessary. Using these conditions, the interferences were completely removed for both waters and sediments and the calibration curve in ultrapure water (1% nitric acid) was linear up to 30 μg/L. The detection limits for waters and sediments were 0.95 μg/L and 0.78 μg/g, respectively. The accuracy of the proposed method for sediments was validated by analyzing certified reference materials (obtained values were within the certified ones) and spiked wetland sediments (mean recovery of 99.0%). Received: 11 October 1998 / Revised: 3 December 1998 / Accepted: 11 March 1999     

Evaluation of tungsten–rhodium coating on an integrated platform as a permanent chemical modifier for cadmium,lead, and selenium determination by electrothermal atomic absorption spectrometry

A tungsten–rhodium coating on the integrated platform of a transversely heated graphite atomizer is proposed as a permanent chemical modifier for the determination of Cd, Pb, and Se by electrothermal atomic absorption spectrometry. It was demonstrated that coating with 250 μg W+200 μg Rh is as efficient as the conventional Mg(NO₃)₂+NH₄H₂PO₄ or Pd+Mg(NO₃)₂ modifiers for avoiding most serious interferences. The permanent W–Rh modifier remains stable for 300–350 firings of the furnace, and increases tube lifetime by 50%–100% when compared to pyrolytic carbon integrated platforms. Also, there is less degradation of sensitivity during the atomizer lifetime when compared with the conventional modifiers, resulting in a decreased need of re-calibration during routine analysis. The characteristic masses and detection limits achieved using the permanent modifier were respectively: Cd 1.1±0.4 pg and 0.020 μgL⁻¹; Pb 30±3 pg and 0.58 μgL⁻¹ and Se 42±5 pg and 0.64μgL⁻¹. Results from the determination of these elements in water reference materials were in agreement with the certified values, since no statistical differences were found by the paired t-test at the 95% level.     

Use of the internal standardization for difficult sampling by graphite furnace atomic absorption spectrometry

This work shows the potentiality of As as internal standard to compensate errors from sampling of sparkling drinking water samples in the determination of selenium by graphite furnace atomic absorption spectrometry. The mixture Pd(NO₃)₂/Mg(NO₃)₂ was used as chemical modifier. All samples and reference solutions were automatically spiked with 500 μg l⁻¹ As and 0.2% (v/v) HNO₃ by the autosampler, eliminating the need for manual dilutions. For 10 μl dispensed sample into the graphite tube, a good correlation (r=0.9996) was obtained between the ratio of analyte absorbance by the internal standard absorbance and the analyte concentrations. The relative standard deviations (R.S.D.) of measurements varied from 0.05 to 2% and from 1.9 to 5% (n=12) with and without internal standardization, respectively. The limit of detection (LD) based on integrated absorbance was 3.0 μg l⁻¹ Se. Recoveries in the 94-109% range for Se spiked samples were obtained. Internal standardization (IS) improved the repeatability of measurements and increased the lifetime of the graphite tube in ca. 15%.     

Analytical quality control by solid sampling GFAAS in the production of animal tissue reference materials: lead and cadmium in bovine liver reference materials

Summary The function of solid sampling graphite furnace atomic absorption spectrometry (SS-GFAAS) in the laboratory-internal preparation, production and standardization of bovine liver reference material is described. Analytical quality assurance was achieved by using a wet digestion decomposition procedure and GFAAS (WD-GFAAS) as well as three different methods of SS-GFAAS. It will be shown, that SS-GFAAS is an adequate and efficacious method of analytical quality control in the production of reference materials. Details are given about the preliminary steps of sample selection and preparation, applying SS-GFAAS both as a screening method and for the detection of contamination during the production of the reference materials. The element contents of the four bovine liver materials measured after decomposition with nitric acid in the open system by GFAAS and also by Flame-AAS, using the slotted tube atom trap, are compared statistically with the results obtained by SS-GFAAS. In solid sampling analyses three different systems were applied: a solid sampling ZAA-spectrometer with platform-boat, a D₂AA-spectrometer with solid sampling graphite tube and platform-drawer and an autoprobe-D₂AA-spectrometer with solid sampling autoprobe and graphite tube.     

Palladium-citric acid-ammonium fluoride as a matrix modifier for overcoming of interferences occurring during the direct determination of Sn in aqua regia extracts from environmental samples by D2-ETAAS

When tin is to be determined in such a complex matrix like aqua regia extracts of environmental samples by electrothermal atomic absorption spectrometry (ETAAS), spectral interferences occur when deuterium-lamp (D₂) background correction is used, even using high pyrolysis temperature of 1400 °C achieved with palladium with citric acid chemical modifier. We have found that the further addition of NH₄F to palladium with citric acid chemical modifier is essential for overcoming the above-mentioned problems for which aluminium oxide is most probably responsible. It is supposed, that NH₄F enables volatilization of the alumina matrix formed by hydrolysis from the chloride salt and interfering in a gas phase via the formation of AlF₃ which could be, in contrast to aluminium oxide, removed from the graphite furnace during the pyrolysis stage. Using the proposed chemical modifier, the direct and accurate determination of Sn in aqua regia extracts from rocks, soils and sediments is possible even when using matrix free standard solutions. This presumption was confirmed by the analysis of certified reference samples and by the comparison with inductively coupled plasma time of flight mass spectrometry (ICP-TOFMS) method. Characteristic mass and LOD value for the original sample (10-μL aliquots of sample) was 17 pg and 0.055 μg g⁻¹, respectively.     

Determination of indium in high purity antimony by electrothermal atomic absorption spectrometry (ETAAS) using boric acid as a modifier

The use of boric acid as a modifier for the determination of trace amount of indium in high purity antimony by electrothermal atomic absorption is described. It was found that the negative influence of the hydrofluoric acid, used for the digestion could not be eliminated by using stabilized temperature platform furnace (STPF) alone. Due to the high dissociation energy (D₀ = 506 kJ mol⁻¹) of indium fluoride, it is difficult to dissociate in the gas phase and hence is lost. In presence of HF (used for the dissolution of antimony), the universal Pd-Mg modifier does not work satisfactorily. Additionally, rising corrosion and reduced tube lifetime were observed when the acid digested (HF-HNO₃) antimony solution was injected in to the platform. Improvement in platform life and elimination of interferences were achieved by the addition of boric acid as a chemical modifier together with ruthenium coating of the platform. Corrosive changes of the transversely heated graphite atomizer (THGA) platform surface were examined by scanning electron microscopy. The standard addition method was applied. A characteristic mass of 36 pg was obtained. The detection limit of the proposed method is around 0.04 μg g⁻¹. The developed method was applied to the determination of indium in real samples. The data obtained by this method were in good agreement with those obtained by ICP-MS.     

Determination of zinc in marine/lacustrine sediments by graphite furnace atomic absorption spectrometry using Pd/Mg chemical modifier and slurry sampling

Effectiveness of Pd/Mg chemical modifier for the accurate direct determination of zinc in marine/lacustrine sediments by graphite furnace atomic absorption spectrometry (GF-AAS) using slurry samples was evaluated. A calibration curve prepared by aqueous zinc standard solution with addition of Pd/Mg chemical modifier is used to determine the zinc concentration in the sediment. The accuracy of the proposed method was confirmed using Certified Reference Materials, NMIJ CRM 7303-a (lacustrine sediment) from National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, Japan, and MESS-3 (marine sediment) and PACS-2 (marine sediment) from National Research Council, Canada. The analytical results obtained by employing Pd/Mg modifier are in good agreement with the certified values of all the reference sediment materials. Although for NRC MESS-3 an accurate determination of zinc is achieved even without the chemical modifier, the use of Pd/Mg chemical modifier is recommended as it leads to establishment of a reliable and accurate direct analytical method. One quantitative analysis takes less than 15 minutes after we obtain dried sediment samples, which is several tens of times faster than conventional analytical methods using acid digested sample solutions. The detection limits are 0.13?µg?g^?1 (213.9?nm) and 16?µg?g^?1 (307.6?nm), respectively, in sediment samples, when 40?mg of dried powdered samples are suspended in 20?mL of 0.1?mol?L^?1 nitric acid and a 10?µl portion of the slurry sample is measured. The precision of the proposed method is 8–15% (RSD).     

Determination of vanadium in water by atomic absorption spectrometry with electrothermal atomization and using hot injection and preconcentration on the graphite tube

A sensitive method for the determination of vanadium in water by atomic absorption spectrometry with electrothermal atomization and using hot injection and preconcentration on the graphite tube is described. The water sample (200 μl) is added to the heated graphite tube in four portions over 200 s. Magnesium nitrate is used as matrix modifier. The precision, accuracy and interferences of the method were investigated. The method allows vanadium down to 0.27 μg l^?1 to be detected.     

A two-step extraction method for differentiating chromium species in water

The hexavalent Cr species Cr(VI) in natural waters can be quantitatively extracted by diethyldithiocarbamate (DDTC) in the pH range 4.0–4.5 into chloroform, followed by back-extraction into a Hg(II) solution for graphite furnace atomic absorption spectrometry (GFAAS). The trivalent Cr(III) species can be oxidized to Cr(VI) by KMnO₄ and then extracted by the DDTC-Hg(II) procedure. The proposed two-step extraction method combined with GFAAS is suitable for Cr speciation studies in natural water systems.     

Green method for ultrasensitive determination of Hg in natural waters by electrothermal-atomic absorption spectrometry following sono-induced cold vapor generation and ‘in-atomizer trapping’

Sono-induced cold vapor generation (SI-CVG) has been used for the first time in combination with a graphite furnace atomizer for determination of Hg in natural waters by electrothermal-atomic absorption spectrometry after in situ trapping onto a noble metal-pretreated platform (Pd, Pt or Rh) inserted into a graphite tube. The system allows ‘in-atomizer trapping’ of Hg without the use of conventional reduction reactions based on sodium borohydride or tin chloride in acid medium for cold vapor generation. The sono-induced reaction is accomplished by applying ultrasound irradiation to the sample solution containing Hg(II) in the presence of an organic compound such as formic acid. As this organic acid is partly degraded upon ultrasound irradiation to yield CO, CO₂, H₂ and H₂O, the amount of lab wastes is minimized and a green methodology is achieved.