Direct analysis of solid samples by graphite furnace atomic absorption spectrometry with a transversely heated graphite atomizer and D2-background correction system (SS GF-AAS)

An instrumental design for the analysis of heavy metals in solid samples (certified reference materials, river sediments, cements) by direct graphite furnace atomic absorption spectroscopy (SSGF-AAS) is presented and outlined. A high performance atomic absorption spectrometer with a D₂-background corrector and a transversely heated graphite atomizer was modified. Solid sampling was achieved by a mechanical module combined with an ultra microbalance. Cadmium, lead and chromium in different samples (sample weights between 20–400 μg) have been determined in the μg/g- to ng/g-range with the graphite-platform technique. Different ways of calibration and inhomogeneity problems are discussed. The precision of SSGF-AAS is equal to the precision of the conventional AAS-technique with chemical digestion (microwave digestion system, Zeeman-AAS). It is shown that SSGF-AAS is a reasonable alternative to the conventional technique for selected analytical problems.     

Direct determination of parts-per-billion levels of germanium in botanical samples and coal fly ash by graphite furnace atomic absorption spectrometry

 Parts-per-billion levels of germanium can be determined directly by graphite furnace atomic absorption spectrometry (GFAAS) using palladium plus strontium as a mixed modifier resulting in pyrolysis temperatures up to 1400 °C without loss of germanium. At this temperature the matrix effect including the most troublesome sulfate interference can be eliminated. Palladium plus strontium nitrate is advantageous compared to palladium alone or palladium plus magnesium nitrate; an amount of 15 μg of sulfate does not show any interference on the determination of 1 ng of germanium. The method was successfully applied to the determination of ng/g levels of germanium in botanical samples and coal fly ash after thermal decomposition of the samples in a mixture of acids using a pressure bomb. The results were consistent with the reference values given for botanical samples and coal fly ash with a recovery range of 96.4∼103.4% Received: 16 September 1996/Revised: 10 December 1996/Accepted: 14 January 1997     

Direct analysis of solid samples by GFAAS – determination of trace heavy metals in barytes

Solid sampling graphite furnace atomic absorption spectroscopy (SS-GFAAS) has been used for the determination of traces of heavy metals (Cd, Pb, Cu, Cr, Ni, V and As) in barytes over a wide concentration range, e.g. Cd from 0.023 to 27.0 μg/g and Pb from 1.54 to 3509 μg/g.The necessity of determining heavy metals in commercial barytes (naturally occurring barium sulfate), a mineral important to the oil industry because of its use in drilling muds, is discussed. The problems presented by the analysis of this difficult matrix are elegantly solved by using SS-GFAAS for the direct determination of heavy metals. A high-performance graphite furnace AAS with D₂-background correction system and a transversely heated graphite atomizer was used for the investigations. The spectrometer was combined with a mechanical sampling module and an ultramicrobalance. The transfer of solid samples (sample weights 0.031–0.686 mg) into the atomizer was carried out by using an optimized graphite platform as the sample carrier. Calibration curve techniques and standard addition methods were employed using external standards (CRMs). Problems associated with signal deformations like multiple peaks, tailing or shoulders are also discussed and possibilities to solve the problems are given. The influence of the homogeneity of solid samples on the precision and accuracy are shown in a real example. The results obtained by SS-GFAAS were compared with results by other methods like X-ray fluorescence spectroscopy (XRF) and flame AAS after aqua regia microwave extraction. This study has demonstrated that SS-GFAAS is a very powerful and easy-to-use method for quick and accurate analysis of barytes. Received: 9 November 1998 / Revised: 29 January 1999 / Accepted: 2 February 1999     

Direct analysis of solid samples by GFAAS – determination of trace heavy metals in barytes

Solid sampling graphite furnace atomic absorption spectroscopy (SS-GFAAS) has been used for the determination of traces of heavy metals (Cd, Pb, Cu, Cr, Ni, V and As) in barytes over a wide concentration range, e.g. Cd from 0.023 to 27.0 μg/g and Pb from 1.54 to 3509 μg/g.The necessity of determining heavy metals in commercial barytes (naturally occurring barium sulfate), a mineral important to the oil industry because of its use in drilling muds, is discussed. The problems presented by the analysis of this difficult matrix are elegantly solved by using SS-GFAAS for the direct determination of heavy metals. A high-performance graphite furnace AAS with D₂-background correction system and a transversely heated graphite atomizer was used for the investigations. The spectrometer was combined with a mechanical sampling module and an ultramicrobalance. The transfer of solid samples (sample weights 0.031–0.686 mg) into the atomizer was carried out by using an optimized graphite platform as the sample carrier. Calibration curve techniques and standard addition methods were employed using external standards (CRMs). Problems associated with signal deformations like multiple peaks, tailing or shoulders are also discussed and possibilities to solve the problems are given. The influence of the homogeneity of solid samples on the precision and accuracy are shown in a real example. The results obtained by SS-GFAAS were compared with results by other methods like X-ray fluorescence spectroscopy (XRF) and flame AAS after aqua regia microwave extraction. This study has demonstrated that SS-GFAAS is a very powerful and easy-to-use method for quick and accurate analysis of barytes. Received: 9 November 1998 / Revised: 29 January 1999 / Accepted: 2 February 1999     

Comparative study on the use of Ir, W and Zr-coated graphite tubes for the determination of chromium in slurries of human scalp hair by electrothermal atomic absorption spectrometry

The use of Ir, W and Zr-coated graphite tubes, as permanent chemical modifiers, was studied for the determination of chromium in human scalp hair by ETAAS using the slurry sampling technique. The use of Mg(NO₃)₂ and Pd, as aqueous chemical modifiers, was also investigated and compared to the use of the permanent chemical modifiers. Scalp hair samples were pulverized using a Zr vibrational ball mill, (mean particle diameter of 0.8 μm) and suspended in ultrapure water. The lowest limit of detection, 44.5 μg kg^–1,was achieved for the use of W-coated graphite tubes. The repeatability of the overall procedures (slurry preparation and ETAAS determination) were 15.7, 14.5 and 16.7% for W- and Zr-coated graphite tubes and Mg(NO₃)₂, respectively. The methods were applied to several reference materials, CRM 397 (human hair), DOLT-1 (dogfish liver) and DORM-1 (dogfish muscle), and the results obtained were in agreement to the certified values. Finally, the methods were applied to several human scalp hair samples from healthy adults. Received: 3 April 1997 / Revised: 12 May 1997 / Accepted: 15 May 1997     

dual stage preconcentration system for flame atomic absorption spectrometry using flow injection on-line ion-exchange followed by solvent extraction

A dual stage preconcentration system based on flow injection on-line ion-exchange and solvent-extraction has been developed for flame atomic absorption spectrometry. Lead is taken as a model trace element. A column packed with Amberlite IRC-718 cation exchanger is incorporated into the FI manifold. The analyte is retained on the column by time-based sample loading and eluted by 1 mol/L HNO₃. The eluate is subsequently merged with potassium iodide and tetrabutylammonium bromide (TBABr), and isobutyl methyl ketone (IBMK). Lead is extracted on-line into IBMK as the ion-pair formed between the iodoplumbate anion and tetrabutylammonium cation. The organic phase is separated from the aqueous phase by a gravity phase separator. 50 μL of concentrate is introduced into the nebulizer-burner system of the spectrometer. An enhancement factor of 550 is achieved with a 30 mL sample consumption at a sampling frequency of 30/h. The precision (relative standard deviation) is 2.4% at 10 μg/L level and the detection limit is 0.3 μg/L (3 σ). The method was successfully applied to the determination of lead in water samples. Received: 19 March 1997 / Revised: 24 June 1997 / Accepted: 27 June 1997     

Determination of antimony in wine by hydride generation graphite furnace atomic absorption spectrometry

 A method was developed for the determination of Sb in wine by electrothermal atomic absorption spectrometry, based on preconcentration by hydride generation with collection directly in the graphite furnace. Thiourea was added for prereduction of Sb(V) to Sb(III). The hydride was directly generated from diluted wine. Palladium was used as modifier in the collection step; the overall efficiency of the hydride/trapping system was found to be 67%. Sb was determined in several samples of red wine; the concentrations found were in the range 0.6 to 5.7 μg/L Sb. The detection limit of the method was 39 pg Sb, corresponding to 0.13 μg/L Sb in wine when 0.3 mL wine was analyzed. Received: 3 November 1995/Revised: 22 February 1996/Accepted: 24 February 1996     

Determination of antimony in wine by hydride generation graphite furnace atomic absorption spectrometry

 A method was developed for the determination of Sb in wine by electrothermal atomic absorption spectrometry, based on preconcentration by hydride generation with collection directly in the graphite furnace. Thiourea was added for prereduction of Sb(V) to Sb(III). The hydride was directly generated from diluted wine. Palladium was used as modifier in the collection step; the overall efficiency of the hydride/trapping system was found to be 67%. Sb was determined in several samples of red wine; the concentrations found were in the range 0.6 to 5.7 μg/L Sb. The detection limit of the method was 39 pg Sb, corresponding to 0.13 μg/L Sb in wine when 0.3 mL wine was analyzed. Received: 3 November 1995/Revised: 22 February 1996/Accepted: 24 February 1996     

Rapid and simple chromatographic separation of V(V) and V(IV) using KH-phthalate and their determination by flame atomic absorption spectrometry

A method was developed for the chromatographic separation of V(V) and V(IV) based on the different sorption forces of these vanadium species in C18 columns in presence of KH-phthalate. The vanadium species were detected with a flame atomic absorption spectrometer with acetylene/N₂O flame. The detection limits (3σ) of V(V) and V(IV) were 0.18 μg/mL and 0.15 μg/mL, respectively. The relative standard deviations (N = 5) are 4.2% and 3.4% for 20–20 μg/mL V(V) and V(IV), respectively. The sampling frequency is 75/h. Because of the special interaction occurring between phthalate and V(IV) on the C18 column and the acetylene/N₂O flame atomic absorption detection, practically no interferences can be detected even in large inorganic matrix. Received: 20 February 1997 / Revised: 2 June 1997 / Accepted: 7 June 1997     

Determination of cadmium in water samples by graphite furnace atomic absorption spectrometry after cloud point extraction

The formation of a complex with 2-(5-brom-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP) and cloud point extraction have been applied to the preconcentration of cadmium followed by its determination by graphite furnace atomic absorption spectrometry (GFAAS) using octylphenoxypolyethoxyethanol (TritonX-114) as surfactant. The chemical variables affecting the separation were optimized. At pH 7.0, preconcentration of only 10 mL of sample in the presence of 0.05% TritonX-114 and 2.5 × 10⁻⁶ M 5-Br-PADAP enabled the detection of 0.04 μg/L cadmium. The enrichment factor was 21 for cadmium. The regression equation was A = 0.0439C(μg/L) + 7.2 × 10⁻³. The correlation coefficient was 0.9995. The precision for 10 replicate determinations at 10 μg/L Cd was 2.7% relative standard deviation (RSD). The proposed method has been applied to the determination of cadmium in water samples. The text was submitted by the authors in English.     

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.     

Direct Analysis of Coffee and Tea for Aluminium Determinationby Electrothermal Atomic Absorption Spectrometry

 A method for direct analysis of tea and coffee samples by using electrothermal atomic absorption spectrometry is described. Coffee and tea from different sources were analyzed without digestion step. For slurry analyses the samples were ground, sieved at 105 μm and then suspended in 0.2% v/v HNO₃ and 10% v/v Triton X-100 medium. For liquid phase aluminium determination the samples were prepared in the same way and only the liquid is introduced directly into the graphite furnace. Calibration was performed by aqueous standards for both cases and the determinations were carried out in the linear range between 50 and 250 μg L⁻¹. The characteristic mass of aluminium and the detection limit were 45 pg and 2 μg L⁻¹, respectively. Using a typical 0.1% m/v coffee slurry sample, the relative standard deviation of measurements (n=15) for repeatability was about 8.2%. Received December 27, 1998. Revision March 18, 1999.     

Immuno-affinity columns versus conventional clean-up: a method-comparison study for the determination of zearalenone in corn

The efficiency of a modern analytical method employing immuno-affinity columns (IACs) is compared to a well established traditional technique with respect to the determination of zearalenone (ZON) in corn in the μg/kg range. Despite of a constant error of about 4 μg/kg in the examined working range of 10–200 μg/kg, analytical data obtained from the analysis of spiked and naturally contaminated samples showed good correspondence for the compared methods. The performance characteristics of immuno-affinity-chromatography as a new clean-up technique for the determination of ZON in corn is reported for the first time and compared to a conventional clean-up procedure Received: 25 March 1997 / Revised: 5 May 1997 / Accepted: 12 May 1997     

Separation and preconcentration of Se(IV)/Se(VI) speciation on algae and determination by graphite furnace atomic absorption spectrometry in sediment and water

A novel method for the separation and preconcentration of Se(IV)/ Se(VI) with algae and determination by graphite furnace atomic absorption spectrometry (GFAAS) has been developed. The Se(VI) is extracted with algae from the solution containing Se(IV)/Se(VI) at pH 5.0, and the remaining Se(IV) is then preconcentrated pH 1.0. The detection limits (3σ, n = 11) of 0.16 μg L^–1 for Se(IV) and 0.14 μg L^–1 for Se(VI) are obtained using 40 mL of solution. At the 2.0 μg L^–1 level the relative standard deviation is 2.6% for Se(IV) and 2.3% for Se(VI). The method has been applied to the determination of Se(IV)/Se(VI) in sediment and water samples. Analytical recoveries of Se(IV) and Se(VI) added to samples are ?97 ± 5% and 102 ± 6% (95% confidence), respectively. Received: 10 February 1999 / Revised: 21 June 1999 / /Accepted: 22 June 1999     

The effect of sample preparation on metal determination in soil by FAAS

Different methods for the determination of several metals in soils by flame atomic absorption spectrometry (FAAS) were investigated. Different procedures for total dissolution of soil: I – HF+HClO₄, H₃BO₃, HCl digestion (conventional heating), II – HF+HClO₄, H₃BO₃ digestion followed by fusion with LiBO₂ (conventional heating) and III – HF+HCl+HNO₃, H₃BO₃ digestion (microwave heating), as well as a leaching procedure with HNO₃+HClO₄, HCl were tested and compared. For quality assessment, the certified reference material S-1 soil was used. For most of the investigated metals, the best accuracy and precision were achieved when the procedure I or III were used. The developed procedure was applied to the analysis of soil samples from crude oil refinery and dump of petroleum origin wastes regions. Received: 22 Dezember 1997 / Revised: 9 February 1998 / Accepted: 12 February 1998     

Mercury analysis in environmental samples by EDXRF and CV-AAS

The analysis of total Hg in various environmental matrices was investigated using energy dispersive X-ray fluorescence (EDXRF) for both powdered and digested samples and cold vapor atomic absorption (CV-AAS) for digested samples. Several microwave decomposition procedures were evaluated with respect to the determination of Hg by CV-AAS and EDXRF. The use of different acid mixtures, microwave power settings and decomposition times were compared as well as the analysis on wet and freeze-dried samples. A set of standard reference samples were used to evaluate the procedures: NBS Citrus leaves (1572), NRC Pine needles (1575), NRC Dogfish muscle tissue (DORM-2), NRC Dogfish liver tissue (DOLM-2), BCR Human hair (397), BCR Coking coal (181) and NRC Marine sediment (PACS-1). An H₂SO₄/HNO₃/H₂O₂ acid mixture was found to be optimal for the complete mineralization and digestion of biological samples for Hg by CV-AAS whereas for EDXRF both the HNO₃/H₂O₂ and H₂SO₄/HNO₃/H₂O₂ acid mixture gave good results. The detection limit of EDXRF could significantly be decreased (from 0.2 μg/g to 0.058 μg/g) by performing the analysis with digested samples. A good agreement was obtained between CV-AAS and EDXRF analysis. The obtained results were also in good agreement with certified values. The methods were applied to environmental samples (coal, trees, leaves, spinach, fish, sediments) and human hair in a coal mining area and in places where they use coal for cooking in Vietnam. Received: 24 February 1997 / Revised: 13 June 1997 / Accepted: 18 June 1997     

Determination of cadmium in indium phosphide by electrothermal atomic absorption spectrometry and ion-selective electrode potentiometry

 Two independent methods for the determination of cadmium in cadmium-doped indium phosphide have been developed. Electrothermal atomic absorption spectrometry (ETAAS) utilized both platform atomization and a chemical modifier composed of magnesium nitrate and orthophosphoric acid. As the matrix mass was found to influence the cadmium sensitivity, matrix matched calibration standards were necessary. The detection limit (3s_B) is 0.20 μg/g for a 100 mg sample. The electrochemical method employed a solid-state cadmium sulfide-silver sulfide electrode as potentiometric sensor. An excess of indium (III) influenced the electrode response. A preliminary chelation-extraction of indium with acetylacetone at pH 5.0 in acetate buffer overcame the interference. The detection limit of the ISE-potentiometric method is 10 μg/g for a 200 mg sample. Two indium phosphide single crystals grown from melts doped with cadmium sulfide or cadmium telluride were analyzed for their cadmium content. Received: 27 August 1996/Revised: 27 January 1997/Accepted: 30 January 1997     

Determination of Selenium and Tin in Human Brain by Graphite Furnace Atomic Absorption Spectrometry

 A method is reported for measuring Se and Sn in human brain tissue. The patients from whom the samples were taken had no diseases in their central nervous system. Microwave energy was applied to digest the brain samples. The digested samples were analyzed without dilution by transversely heated graphite atomizer for atomic absorption spectrometry with longitudinal Zeeman background correction. The dependence of integrated absorbance on various chemical modifiers has been examined. The most appropriate technique proved to be 5 μl sample injection using 20 μg prereduced palladium-nitrate for Se determination, and 20 μl sample injection applying 10 μg palladium-nitrate + 3 μg magnesium-nitrate for the measurements of Sn. The optimal temperature program was found to be 1200 °C pyrolysis and 2100 °C atomisation temperature for Se and 1500 °C pyrolysis and 2300 °C atomisation temperature for Sn. Accuracy of the applied techniques was tested by the analysis of standard reference materials. The precision was ±5% for Se and ±10% for Sn. The range of recovery values was 85–95% for Se and 95–105% for Sn. The mean Se concentrations in the investigated brain parts ranged from 200 to 700 ng/g, while the Sn concentrations were between 20 and 300 ng/g dry weight. Received October 3, 2000. Revision February 1, 2001.     

A study of sample mineralization methods for arsenic analysis of blood and urine by hydride generation and graphite furnace atomic absorption spectrometry

Mineralization procedures for blood and urine suitable for the determination of arsenic by Hydride Generation Atomic Absorption Spectrometry (HGAAS) are studied on model samples, and the results are utilized in biological monitoring investigations. The objective of this work is to obtain good total As recoveries for both matrices regardless of added As species (As(III), As(V), DMA, MMA, AsB, or AsC). Prior to the HGAAS analyses, preparation procedures were controlled under optimised conditions by graphite furnace atomic absorption spectrometry (GFAAS). Two preparation procedures for urine give As recoveries close to 100% by HGAAS: a) dry ashing at 420°C with Mg(NO₃)₂ on a hot plate, and b) microwave oven decomposition with (NH₄)₂S₂O₈. For blood samples, As recoveries by HGAAS range between 95 and 108% for all species when using dry ashing after a pretreatment of samples with HNO₃ and H₂O₂ in a microwave oven. Wet digestion with (NH₄)₂S₂O₈ in a microwave oven gives recoveries very near 100% for As _inorg. and MMA. For other As species in spiked blood samples, recoveries of less than 20% As are found. Precision and detection limits obtained by both techniques are evaluated as well. For arsenic concentrations of 20 μg dm⁻³ or more in blood and urine, a chemical modifier is recommended for GFAAS analysis; it may or may not be proceeded by a mineralization step. For low As levels encountered in the unexposed population, the HGAAS technique provides reliable results only if a very complete mineralization procedure is used.     

Anodic stripping voltammetric determination of Zn, Pb and Cu traces in whisky samples

The simultaneous “in natura” determination of trace Zn, Pb and Cu in whisky samples by anodic stripping voltammetry (ASV), using a hanging mercury drop electrode, without previous treatment or addition of supporting electrolyte is described. The choice of an appropriate stripping voltammetric method and deposition potential minimizes the influence of the organic content and ensures a good reproducibility of the measurements. The reliability of the method was tested comparing the results with those of atomic absorption spectroscopy (AAS), with differences of about 10%. The method allows the determination of heavy metal ions in the μg L^–1 range. Received: 14 August 1997 / Revised: 10 December 1997 / Accepted: 11 December 1997