Determination of Al, Cu, Li and Mn in spruce seeds and plant reference materials by slurry sampling graphite furnace atomic absorption spectrometry

An ultrasonic slurry sampling graphite furnace AAS method was developed for the determination of Al, Cu, Li and Mn in spruce seeds, NBS SRM 1575 pine needles and GBW CRM 07602 bush branches and leaves. The only sample preparation was grinding in a Mixer Mill before preparing a slurry by adding 0.14 mol/L nitric acid to a small sample aliquot. Cryogenic grinding was used for the spruce seeds to solve the problem of agglomerating during grinding at room temperature. A modified sample tray was applied allowing the use of both the commercial 1.5 mL vials and home-made 15 mL vials. With optimal conditions for ultrasonic agitation the homogeneity and particle size distributions in the slurries prepared in the two different vials were similar. Several aspects of the slurry sampling approach are discussed and data of important parameters are given, including the total number of particles injected into the graphite furnace, densities of the materials and percentage of analyte extracted into the liquid phase of the slurry. The density of the materials was determined by two methods; by using a Coulter particle analyser and by using a gravimetric method. The two methods gave similar accuracy and precision. The concentration ranges of the elements (in μg g^–1) were: 80–2100 for Al, 3–15 for Cu, 0.06–2.5 for Li and 50–700 for Mn. External calibration with aqueous standards was employed. Chemical modifiers were not found to be necessary. The relative standard deviations were in the range 1.7–7%. Analyses of the two certified plant reference materials confirmed the accuracy of the method. In addition no significant difference was found for analyses of digested and slurried spruce seeds. The detection limit was 10 ng g^–1 for Li and 170 ng g^–1 for Cu. The characteristic mass (area measurements) was 4.4 pg for Li and 11 pg for Cu. For Al and Mn less sensitive wavelengths were used.     

Graphite furnace atomic absorption spectrometry used for determination of total, EDTA and acetic acid extractable chromium and cobalt in soils

Methods for determination of both the total and extractable content of Cr and Co in soil samples were investigated. For the total content of metal, ultrasonic slurry sampling graphite furnace atomic absorption spectrometry was used and compared with conventional analyses after microwave digestion. The influence of grinding, leaching and homogeneity for slurry sampling was also examined. The concentration of the elements in the analyzed materials were in the range: 50 microg g(-1)-0.4% for Cr and 8-14 microg g(-1) for Co. Relative standard deviations (slurry sampling) were in the range 3%-12% for Cr and 0.3%-6% for Co determinations. The detection limit and characteristic mass (peak-area measurements) for Co were 0.14 microg g(-1) and 12.6 pg, respectively. For Cr less sensitive wavelengths were used. Excellent agreement with certified reference material was found for total Cr and Co using slurry sampling. EDTA and acetic acid extractions were performed, using protocols given by the Measurement and Testing Programme of the European Commission. The percentages extracted for the different soil samples were 0.3-1.0 for Cr and 2.5-24 for Co. To validate the accuracy of the extractable Cr, CRM 483 Sewage sludge amended soil was analyzed. The values found were 37% and 32% higher than the certified value for EDTA and acetic acid extractable Cr, respectively. The precision for extractable concentration of Cr and Co was about 6% or less. External calibration with aqueous standards, matched to contain the same reagents as the samples, was employed.     

Determination of titanium by slurry sampling graphite furnace atomic absorption spectrometry with the use of fluoride modifiers

A method for the determination of titanium in graphite furnace atomic absorption spectrometry with slurry sampling was developed. Titanium forms thermally stable carbides in the graphite tube that leads to decreased sensitivity and severe memory effects. Various fluorinating agents, BaF(2), NH(4)F, and CHF(3) (Freon-23) were therefore examined in order to reduce or eliminate these problems. Ti was determined, at various concentration levels, in certified reference materials (CRMs) using ultrasonic slurry sampling graphite furnace atomic absorption spectrometry (USS-GFAAS). The three CRMs, GBW 07601 (Human Hair Powder), GBW 07602 (Bush Branches and Leaves), and GBW 07411 (Chinese Soil), contained 2.7 microg g(-1), 95 microg g(-1), and 0.41% Ti, respectively. For comparison, determinations of Ti were made with modifiers (BaF(2) and NH(4)F) and without modifier, using 5% CHF(3) (in argon) for cleaning the graphite furnace. Good accuracy was obtained using aqueous Ti standards for calibration. A homogeneity study showed that Ti was evenly distributed in all the samples at the mg-microg level. The relative standard deviations (RSDs) obtained for the three CRMs were 16%, 11%, and 8% ( n=30). In spite of the wide range of Ti concentrations in the present samples, the same wavelength (365.4 nm) could be used for analysis by varying the slurry sample concentration. The precision was best for the material with the highest titanium content in spite of the fact that only 3 microg of sample was introduced into the furnace.     

Analysis of standard reference materials after microwave-oven digestion in open vessels using graphite furnace atomic absorption spectrophotometry and Zeeman-effect background correction

Summary Heating-covered teflon digestion vials located inside a reheatable container in the presence of different acid mixtures with microwave oven dissolve the metals from biological and environmental certified reference materials. Pb, Cd, Cu, Mn and Fe from the dissolved samples are determined by graphite furnace atomic absorption spectrophotometry and Zeeman-effect background correction. The method allows the treatment of about 100 samples per operation.     

Direct determination of Cu,Mn, Pb,and Zn in beer by thermospray flame furnace atomic absorption spectrometry

In this work, thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) was employed for Cu, Mn, Pb, and Zn determination in beer without any sample digestion. The system was optimized and calibration was based on the analyte addition technique. A sample volume of 300 μl was introduced into the hot Ni tube at a flow-rate of 0.4 ml min⁻¹ using 0.14 mol l⁻¹ nitric acid solution or air as carrier. Different Brazilian beers were directly analyzed after ultrasonic degasification. Results were compared with those obtained by graphite furnace atomic absorption spectrometry (GFAAS). The detection limits obtained for Cu, Mn, Pb, and Zn in aqueous solution were 2.2, 18, 1.6, and 0.9 μg l⁻¹, respectively. The relative standard deviations varied from 2.7% to 7.3% (n=8) for solutions containing the analytes in the 25–50 μg l⁻¹ range. The concentration ranges obtained for analytes in beer samples were: Cu: 38.0–155 μg l⁻¹; Mn: 110–348 μg l⁻¹, Pb: 13.0–32.9 μg l⁻¹, and Zn: 52.7–226 μg l⁻¹. Results obtained by TS-FF-AAS and GFAAS were in agreement at a 95% confidence level. The proposed method is fast and simple, since sample digestion is not required and sensitivity can be improved without using expensive devices. The TS-FF-AAS presented suitable sensitivity for determination of Cu, Mn, Pb, and Zn in the quality control of a brewery.     

Determination of manganese, iron and copper in sodium by chemical modification/graphite furnace atomic absorption spectrometry

Trace Mn, Fe and Cu in sodium were determined by chemical modification/graphite furnace atomic absorption spectrometry. The sodium sample was changed into NaOH in a desiccator by room temperature water vapor generated under reduced pressure, then the NaOH was dissolved in water and HNO(3) was added to give a clear solution. The solution was analysed by chemical modification/graphite furnace atomic absorption spectrometry. A nickel nitrate modifier was effective in improving integrated absorbance signals and the reproducibility of measurement. Analytical results for Mn, Fe and Cu were 170, 970 and 210 ng/g and relative standard deviations (n = 5) were 3.5, 5.8 and 6.7%, respectively. These results agreed with the values obtained from a chelating resin preconcentration/ICP-AES method.     

Transport efficiencies and analytical determinations with electrothermal vaporization employing electrostatic precipitation and electrothermal atomic spectroscopy

Analyte transport efficiencies of solid as well as liquid samples were determined for electrothermal vaporization (ETV). A graphite furnace of the boat-in-tube type was employed for ETV. The generated aerosol was transported by an argon flow via a tubing into an external precipitator and deposited on a L’vov platform with a corona-like discharge. The sample on the secondary platform was analysed with a laboratory-constructed coherent forward scattering multielement spectrometer. For determining the analyte transport efficiencies, the comparative measurements were carried out with standard solutions dosed directly on the platform in the spectrometer furnace. The simultaneously investigated elements were Cu, Fe and Mn in the standard reference material BCR CRM 189 wholemeal flour and in a multielement standard solution containing approximately the same element ratio as certified for the solid sample. ETV boat-to-L’vov platform transport efficiencies of approximately 19% for Cu, 24% for Fe and 19% for Mn were calculated for both solid samples and multielement standard solutions. Cu, Fe and Mn in wholemeal flour were determined simultaneously by calibrating against aqueous multielement standard solutions injected into the boat as well as by the standard addition method. The results agree satisfactorily, the deviations from the certified values are below 10% and the relative standard deviations are typically 5–8%. The limits of detection are 250 pg for Cu (λ=324.8 nm), 230 pg for Fe (λ=248.3 nm) and 90 pg for Mn (λ=279.8 nm), loaded into the ETV boat.     

Study of a microwave induced argon plasma sustained in a TE101 cavity as spectrochemical emission source coupled with graphite furnace evaporation

The argon MIP sustained in a TE₁₀₁ cavity has been evaluated as a spectrochemical radiation source and its analytical performance in combination with graphite furnace evaporation has been studied. A quartz discharge tube with a side arm is used, through which the sample vapour from the furnace is introduced by the carrier gas. A stable quasi-toroidal rotating plasma with a central channel could be maintained within a wide range of operating conditions. Under the compromise conditions established, the detection limits for Ag, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Tl are 4, 120, 8, 305, 47, 24, 55, 11, 220, 56 and 28 pg, respectively. The presence of Na results in line intensity enhancements in most cases, which are proportional to the Na amount in the range of 60 ng to 10 μg. By the addition of microgram amounts of Pd, acting partly as a chemical modifier in the furnace and eventually as a buffer in the plasma, the matrix effect caused by Na could be eliminated or largely reduced. The present system has been applied to the determination of 16–800 μg/g amounts of Cu, Fe and Mn in a certified tea sample, and 0.35–71 μg/g amounts of Ag, Cu, Fe, Mn and Pb in a certified human hair sample.     

Slurry sampling for graphite furnace atomic absorption spectrometry

Summary Slurry preparations are an effective way to introduce solids into the graphite furnace. Ultrasonic agitation keeps samples mixed prior to analysis. Several aspects of the ultrasonic slurry sampling approach are discussed including contamination concerns, analyte partitioning, and the effect of particle size. In addition, sample preparation strategies for slurry preparations of non-powdered materials are reviewed. The suitability of this method for assessing homogeneity is demonstrated.     

Slurry sampling for the determination of thallium in soils and sediments by graphite furnace atomic absorption spectrometry

The analytical conditions for thallium determination in soils and sediments by slurry sampling graphite furnace atomic absorption spectrometry were studied and optimized. Elimination of a strong background for soils rich in organic materials by application of tungsten carbides coated graphite tubes/platforms was studied in detail. Tungsten carbides increased the maximum permissible pyrolysis temperature from 300 to 900 degrees C. The mechanism of tungsten carbide formation on different graphite surfaces was proposed. Application of a strong basic anion-exchange resin for interference elimination in thallium determination in marine sediments was described. Calibration was performed directly using aqueous standards both for soil and sediment analysis. Analysis of CRM confirmed the reliability of the approach. The precision and accuracy of thallium determination by the described method for soils and sediments was acceptable. A characteristic mass of 13.8 pg was obtained and the limit of detection for the proposed method was around 0.06 microg g(-1) Tl.     

Method development for the determination of cadmium,copper, lead,selenium and thallium in sediments by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry and isotopic dilution calibration

A procedure for the determination of Cd, Cu, Pb, Se and Tl by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) with calibration by isotopic dilution is proposed. The slurry is prepared by mixing the sample with diluted nitric and hydrofluoric acids in an ultrasonic bath and then in a water bath at 60 °C for 120 min. The slurries were let to stand at least for 12 h, manually shaken before poured into the autosampler cups and homogenized by passing through an argon flow, just before pipetting it into the furnace. The analytes were determined in two groups, according to their thermal behaviors. The furnace temperature program was optimized and the selected compromised pyrolysis temperatures were: 400 °C for Cd, Se and Tl and 700 °C for Cu and Pb. The vaporization temperature was 2300 °C. The analyses were carried out without modifier as no significant effect was observed for different tested modifiers. Different sample particle sizes did not affect the sensitivity significantly, then a particle size ≤50 μm was adopted. The accuracy was checked by analyzing five certified reference sediments, with analytes concentrations from sub-μg g⁻¹ to a few hundreds μg g⁻¹. The great majority of the obtained concentrations were in agreement with the certified values. The detection limits, determined for the MESS-2 certified sediment, were, in μg g⁻¹: 0.01 for Cd; 0.8 for Cu; 0.4 for Pb; 0.4 for Se and 0.06 for Tl. The precision was adequate with relative standard deviations lower than 12%. Isotopic dilution showed to be an efficient calibration technique for slurry, as the extraction of the analyte to the liquid phase of the slurry and the reactions in the vaporizer must help the equilibration between the added isotope and the isotope in the sample.     

Direct analysis of coal by electrothermal atomization atomic-absorption spectrometry

A novel approach for trace element determination in coal samples is described, based on grinding the sample to less than 200 mesh, "pipetting" the material into a tube-cup furnace, and measurement by electrothermal atomization atomic-absorption spectrometry. Either solid standard reference materials or aliquots of solutions of Pb, Zn and Mn can be used to prepare analytical calibration curves. The SRMs are diluted with spectroscopic grade graphite prior to introduction into the tube-cup furnace. After the atomization and cleaning step, any remaining ash is removed with a Pasteur pipette. The measured values for Pb, Zn and Mn agree well with the certified SRM values. The method is rapid, and sufficiently precise (5-14%) and accurate (within 5-12% of standard reference values).     

Flow Injection Semi-online Preconcentration Graphite Furnace Atomic Absorption Spectrometry for Determination of Cadmium, Copper and Manganese

IntroductionGraphite furnace atomic absorption spectrome-try (GFAAS) is one of the most sensitive tech-niques for the determination of various elementswith detection limits in the range ofμg/ L to ng/ L.Despite the impressive detection power of the tech-nique,GFAAS can tbe routinely used to make di-rect analysis of some real samples with complexcomposition[1] . This is due to the matrix interfer-ence and/ or insufficient detection power. Conse-quently,separation and preconcentration proc…     

Trace analysis of gallium arsenide by selective evaporation of the matrix with bromine vapours

Gallium arsenide samples are analyzed by graphite furnace AAS after the selective evaporation of the matrix elements as bromides with bromine vapours in a simple apparatus. The evaporation step is carried out at 280–300 ° C and it is accomplished for 0.5 g sample within 1 h. Reproducibilities of 5 to 20% were obtained. Detection limits (3 s, in ng/g) are 20 (Fe), 5.0 (Ca), 3.0 (Mg), 2.0 (Ni, Cu), 1.0 (Al), 0.5 (Pb, Co), 0.2 (Mn, Cr).     

Direct determination of silicon in powdered aluminium oxide by use of slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry

A direct method for determination of silicon in powdered high-purity aluminium oxide samples, by slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry (GF-AAS), has been established. A slurry sample was prepared by 10-min ultrasonication of a powdered sample in an aqueous solution containing both sodium carbonate and boric acid as a mixed flux. An appropriate portion of the slurry was introduced into a pyrolytic graphite furnace equipped with a platform. Silicon compounds to be determined and aluminium oxide were fused by the in situ fusion process with the flux in the furnace under optimized heating conditions, and the silicon absorbance was then measured directly. The calibration curve was prepared by use of a silicon standard solution containing the same concentration of the flux as the slurry sample. The accuracy of the proposed method was confirmed by analysis of certified reference materials. The proposed method gave statistically accurate values at the 95% confidence level. The detection limit was 3.3 microg g(-1) in solid samples, when 300 mg/20 mL slurry was prepared and a 10 microL portion of the slurry was measured. The precision of the determination (RSD for more than four separate determinations) was 14% and 2%, respectively, for levels of 10 and 100 microg g(-1) silicon in aluminium oxide.     

Advances in ultrasonic slurry graphite furnace atomic absorption spectrometry

Summary Ultrasonic slurry graphite furnace atomic absorption spectrometry is a useful technique for automated direct analysis of solids. The effectiveness of ultrasonic agitation for mixing samples is demonstrated. This analytical approach is evaluated to identify sources of imprecision. Strategies for optimizing slurry preparations are discussed, focusing on particle size, density, analyte partitioning, and sampling limitations. Finally, a teflon bead method is presented for grinding biological and botanical samples. An optimized general approach for ultrasonic slurry sampling is presented.Presented at the 5th International Colloquium on Solid Sampling with Atomic Spectroscopy, May 18–20, 1992; Geel, Belgium. Papers edited by R. F. M. Herber, Amsterdam.     

Direct sample introduction of wines in graphite furnace atomic absorption spectrometry for the simultaneous determination of arsenic, cadmium, copper and lead content

A multi-element graphite furnace atomic absorption spectrometry (GFAAS) method was elaborated for the simultaneous determination of As, Cd, Cu, and Pb in wine samples of various sugar contents using the transversally heated graphite atomizer (THGA) with end-capped tubes and integrated graphite platforms (IGPs). For comparative GFAAS analyses, direct injection (i.e., dispensing the sample onto the IGP) and digestion-based (i.e., adding oxidizing agents, such as HNO(3) and/or H(2)O(2) to the sample solutions) methods were optimized with the application of chemical modifiers. The mixture of 5 microg Pd (applied as nitrate) plus 3 microg Mg(NO(3))(2) chemical modifier was proven to be optimal for the present set of analytes and matrix, it allowing the optimal 600 degrees C pyrolysis and 2200 degrees C atomization temperatures, respectively. The IGP of the THGA was pre-heated at 70 degrees C to prevent the sputtering and/or foaming of sample solutions with a high organic content, dispensed together with the modifier solution, which method also improved the reproducibility of the determinations. With the digestion-based method, the recovery ranged between 87 and 122%, while with the direct injection method it was between 96 and 102% for Cd, Cu, and Pb, whereas a lower, compromise recovery of 45-85% was realized for As. The detection limits (LODs) were found to be 5.0, 0.03, 1.2, and 0.8 microg l(-1) for As, Cd, Cu, and Pb, respectively. The characteristic mass (m(0)) data were 24 pg As, 1.3 pg Cd, 13 pg Cu, and 35 pg Pb. The upper limits of the linear calibration range were 100, 2, 100, and 200 microg l(-1) for As, Cd, Cu, and Pb, respectively. The precisions were not worse than 4.8, 3.1, 3.7, and 2.3% for As, Cd, Cu, and Pb, respectively. For arsenic, a higher amount of the modifier (e.g., 20 microg Pd plus 12 microg Mg(NO(3))(2)) could be recommended to overcome the interference from the presence of sulphate and phosphate in wines. Although this method increased the sensitivity for As (m(0)=20 pg), it also enhanced the background noise, thus only a slight improvement in the LOD of As (3.9 microg l(-1)) was realized. For the 35 red and white wine samples studied, the highest metal contents were observed for Cu ranging from 20 to 640 microg l(-1) (average: 148 microg l(-1)), followed by Pb from 6 to 90 microg l(-1) (average: 32.3 microg l(-1)), and Cd from 0.05 to 16.5 microg l(-1) (average: 1.06 microg l(-1)), whereas the As content was below the LOD. This wide fluctuation in the trace metal content could be associated with the origin of wines from various regions (i.e., different trace metal level and/or quality of soil, and/or anthropogenic impact), and with diverse materials (e.g., additives and containers) involved in the wine production processes. The Cu content of wine samples was significantly correlated with Pb, whereas its weak anti-correlation was found with Cd. Interestingly, the level of Pb was anti-correlated with the year of production of the wines. This is likely due to the gradual decrease in the Pb content of soils of vineyards by time, which certainly causes less Pb-uptake of the grape plant, thus a decrease in the Pb content of wines as well.     

Determination of metal content in valerian root phytopharmaceutical derivatives by atomic spectrometry

Phytopharmaceuticals containing Valerian are used as mild sleep-inducing agents. The elemental composition of 3 different marks of Valeriana officinalis roots commercially available in the Argentinian market, their teas, and a commercial tincture have been studied. The content of Al, Ca, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, V, and Zn was determined in phytopharmaceuticals by flame atomic emission/absorption spectrometry, electrothermal atomic absorption spectrometry, and ultrasonic nebulization coupled to inductively coupled plasma-optical emission spectrometry. Prior to analyses of the samples, a digestion procedure was optimized. The analytical results obtained for Fe, Al, Ca, and V in the solid sample study were within the range 100-1000 mg/kg, and for Mn, Zn, and Pb within the range 10-100 mg/kg. Cadmium was found at levels up to 0.0125 mg/kg.     

Simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by slurry-sampling graphite furnace AAS.

A fast and accurate analytical method was established for the simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by graphite furnace atomic absorption spectrometry using a slurry sampling technique and a Hitachi Model Z-9000 atomic absorption spectrometer. The slurry samples were prepared by the ultrasonication of silicon carbide or silicon nitride powders with 0.1 M nitric acid. Calibration curves were prepared by using a mixed standard solution containing aluminum, calcium, iron and 0.1 M nitric acid. The analytical results of the proposed method for aluminum, calcium and iron in silicon carbide and silicon nitride reference materials were in good agreement with the reference values. The detection limits for aluminum, calcium and iron were 0.6 microg/g, 0.15 microg/g and 2.5 microg/g, respectively, in solid samples, when 200 mg of powdered samples were suspended in 20 ml of 0.1 M nitric acid and a 10 microl portion of the slurry sample was then measured. The relative standard deviation of the determination of aluminum, calcium and iron was 5 - 33%.     

Trace analysis of gallium arsenide by graphite furnace AAS

Summary Crystalline and powdered gallium arsenide samples are analysed by graphite furnace AAS. The sample is dissolved in hydrochloric acid and bromine, ammonium chloride as matrix modifier is added and the matrix elements are selectively evaporated as chlorides and bromides in the graphite tube of the atomizer before the atomization step. The temperature programs are optimized. The accuracy of the results was checked by recovery tests and by ICP-OES. The detection limits (g/g) are 0.1 (Ca, Fe), 0.05 (Zn, Pb), 0.03 (Mg), 0.01 (Al, Ni, Cu), 0.005 (Co), 0.002 (Cr) and 0.001 (Mn).

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Spurenanalyse von Galliumarsenid durch Graphitrohr-AAS