Preconcentration of cobalt with 8-hydroxyquinoline and gas chromatographic stationary phase Chromosorb 105 and its determination by graphite furnace atomic absorption spectrometry

This paper presents a study of the adsorption characteristics of a commercially available GC stationary phase Chromosorb 105 for Co²⁺, which can be successfully applied to the preconcentration of Co²⁺ in water samples followed by GFAAS determination. After reacting with 8-hydroxyquinoline to form a complex at pH 8.0, Co²⁺ in water can be retained on a minicolumn packed with Chromosorb 105 and eluted with 2.5 ml of a mixture of ethanol and 2 mol l⁻¹ HNO₃ (2+1, v/v). The recoveries of Co²⁺ from 200 ml of tap water, river water and bottled natural mineral water samples are quantitative. Conditions for quantitative and reproducible preconcentration, elution and subsequent GFAAS determination were studied. A highly sensitive, simple method for preconcentration and GFAAS determination of trace amount of cobalt in natural water samples using a Chromosorb 105 packed minicolumn has been proposed. The high retention efficiency (95%) for Co²⁺ provides a sensitivity enhancement of 80 for a 200 ml sample volume with a detection limit of 13.4 ng l⁻¹ (3σ) and a quantification limit of 44.5 ng l⁻¹ (10σ).     

Preconcentration of trace amounts of beryllium in water samples on octadecyl silica cartridges modified by quinalizarine and its determination with atomic absorption spectrometry

A simple method has been developed for rapid and selective extraction, preconcentration and determination of trace amounts of beryllium. The extraction is carried out by octadecyl silica cartridge, modified with quinalizarine as a chelating agent. The effect of different parameters, such as sample matrix, flowrates of sample solution and eluent, pH, type and least amount of eluent for elution of Be(+2) ions from cartridge, breakthrough volume and limit of detection, were evaluated. Also, the effects of various cationic and anionic interferences on percent recovery of Be(+2) were studied. Be(+2) was extracted from solution at pH 6-6.6 and was eluted from modified cartridge with 5 ml of 0.5 M HNO(3). Extraction efficiencies >99% were obtained by elution of the cartridges with minimal amount of eluent. A preconcentration factor of 200 and a detection limit of 200 ng per 1000 ml were obtained. The method was applied to the recovery and determination of Be(+2) in different water and alloy samples.     

Preconcentration of trace amounts of silver ion in aqueous samples on octadecyl silica membrane disks modified with hexathia-18-crown-6 and its determination by atomic absorption spectrometry

A simple and reliable method has been developed to selectively separate and concentrate trace amounts of silver ion from aqueous samples for the subsequent measurement by atomic absorption spectrometry. Ag+ ions are absorbed quantitatively during passage of aqueous samples through an octadecyl-bonded silica membrane disk modified by hexathia-18-crown-6. Almost all matrix elements will pass through the disk to drain. The retained Ag+ ions are then stripped from the disk with a minimal amount of thiosulfate solution as eluent. The proposed method permitted large enrichment factors of about 200 and higher. The limit of detection of the proposed method is 50 ng Ag+ per 1,000 mL. The effects of various cationic interferences on the recovery of silver in binary mixtures were studied. The method was applied to the recovery of Ag+ ions from different synthetic and water samples.     

Preconcentration of trace amounts of silver ion in aqueous samples on octadecyl silica membrane disks modified with hexathia-18-crown-6 and its determination by atomic absorption spectrometry

A simple and reliable method has been developed to selectively separate and concentrate trace amounts of silver ion from aqueous samples for the subsequent measurement by atomic absorption spectrometry. Ag⁺ ions are absorbed quantitatively during passage of aqueous samples through an octadecyl-bonded silica membrane disk modified by hexathia-18-crown-6. Almost all matrix elements will pass through the disk to drain. The retained Ag⁺ ions are then stripped from the disk with a minimal amount of thiosulfate solution as eluent. The proposed method permitted large enrichment factors of about 200 and higher. The limit of detection of the proposed method is 50 ng Ag⁺ per 1000 mL. The effects of various cationic interferences on the recovery of silver in binary mixtures were studied. The method was applied to the recovery of Ag⁺ ions from different synthetic and water samples. Received: 28 September 1999 / Revised: 2 December 1999 / Accepted: 8 December 1999     

Determination of trace amounts of gold in acid-attacked environmental samples by atomic absorption spectrometry with electrothermal atomization after preconcentration

A method for determination of trace amounts of gold in environmental samples (rocks, soils, sediments, and waters) by atomic absorption spectrometry with electrothermal atomization (ETAAS) after preconcentration using a chelating sorbent Spheron Thiol 1000 is described. The method accurately determines gold between 0.001 and several tens of grams per ton in samples having complex variations in mineralogy. Pulverized samples are roasted at 650°C to oxidize any sulfide and/or carbonaceous material. Samples are then subjected to a series of acid treatments to eliminate any silica matrix and to dissolve the sample. The Spheron Thiol 1000 is added to the sample solution, and then with sorbed gold is filtered out, washed, and ignited at 550°C. The residue is dissolved in aqua regia, evaporated, dissolved in distilled water, transferred to a volumetric flask, and analyzed by ETAAS.The limits of detection of gold, based on the 3 definition, were 0.5 ng g^–1 for 10-g samples (rocks, sediments, soils) and 0.05 ng mL^–1 for 1-L water samples. Precision of determination expressed by the relative standard deviation varied from 2.9% to 16.4%. The accuracy of the method is verified by analysis of certified reference materials. The obtained analytical results are in good agreement with attested values. The developed method was applied for gold determination in environmental samples affected by the acidification (acid mine drainage which is mainly a product of pyrite oxidation) from an open quartzite mine in the obov region situated NE of the city of Banská tiavnica (Slovakia).     

Preconcentration of gallium by coprecipitation with synthetic zeolites prior to determination by electrothermal atomic absorption spectrometry.

Synthetic zeolites were dissolved in nitric acid, and the resulting solution used as a coprecipitant for the preconcentration of trace amounts of gallium in water samples prior to determination by electrothermal atomic absorption spectrometry (ETAAS). The gallium preconcentration conditions and the ETAAS measurement conditions were optimized. Gallium was quantitatively concentrated with the zeolites coprecipitate from pH 6.0 to 8.0. The coprecipitate was easily dissolved in nitric acid, and an aliquot of the resulting solution was introduced directly into a tungsten metal furnace. The atomic absorbance of gallium in the resulting solution was measured by ETAAS. An ashing temperature of 400 degrees C and an atomizing temperature of 2600 degrees C were selected. The calibration curve was linear up to 3.0 microg of gallium and passed through the origin. The detection limit (S/N > or = 3) for gallium was 0.08 microg/100 cm3. The relative standard deviation at 1.0 microg/100 cm3 was 3.0% (n = 5). The proposed method has been successfully applied to trace gallium analysis in environmental water samples.     

Preconcentration and determination of ultra trace amounts of palladium in water samples by dispersive liquid-liquid microextraction and graphite furnace atomic absorption spectrometry

A highly sensitive, simple and rapid method is presented for the determination of palladium using graphite furnace atomic absorption spectrometry after its separation and preconcentration by dispersive liquid-liquid microextraction. Ultra traces of Pd were extracted and preconcentrated in acidic water samples by using 2-amino-1-cyclohexene-1-dithiocarboxylic acid as a suitable chelating agent, and carbon tetrachloride and acetone as extraction and disperser solvents, respectively. The experimental parameters were optimized in order to enhance the extraction efficiency. After optimizing the extraction conditions and various instrumental parameters, an enhancement factor of 350 was obtained. The analytical curve absorbance vs. concentration was linear over the range 0.02–0.6 µg L^-1 Pd. The detection limit and relative standard deviation were 0.007 µg L^-1 and 4.2%, respectively. The method was successfully applied to the determination of palladium in roadside soil and several aqueous samples.     

Solvent extraction of cadmium as a previous step for its determination in biological samples by electrothermal atomization atomic absorption spectrometry

A method is proposed for the solvent extraction of cadmium using 1,5-bis(di-2-pyridylmethylene)thiocarbohydrazide (DPTH) as extractant. The optimum extraction conditions were evaluated from a critical study of the effect of pH, concentration of extractant, shaking time and ionic strength. The maximum volume ratio of the aqueous to organic phase was 30:1 for a single-stage extraction of99-100% of the metal ion. The detection limit is 0.01 ng/ml cadmium, and the calibration is linear from 0.1 to 5 ng/ml. The relative standard deviation for 10 replicate measurements is 1.8% for 2 ng/ml cadmium. The extraction method was applied to the determination of cadmium in some biological materials using graphite furnace atomic absorption spectrometry.     

Preconcentration of trace heavy metals in water by coprecipitation with magnesium oxinate for electrothermal atomic absorption spectrometry

Nanogram quantities of heavy metals in 200 ml of water were quantitatively preconcentrated by coprecipitation with magnesium oxinate at pH 9–9.5. The precipitate was collected on a 1-m Nuclepore membrane filter and then dissolved in 5 ml of 1 mol/l nitric acid. After diluting to 10 ml with water, a 10- or 20-l aliquot of the solution was directly analyzed by electrothermal atomic absorption spectrometry using deuterium background correction. The background absorption due to the collector magnesium oxinate was negligibly small. The optimized coprecipitation technique has been applied to the determination of cobalt, nickel, copper, cadmium and lead at the ppt level in river and seawater. The relative standard deviations were within 10% and the detection limits were 0.025 (for Co), 0.019 (for Ni), 0.006 (for Cu), 0.001 (for Cd) and 0.017 g/l (for Pb). Blanks through the whole procedure were not detectable.     

Simultaneous determination of cadmium and lead in wine by electrothermal atomic absorption spectrometry

A method has been developed for the direct simultaneous determination of Cd and Pb in white and red wine by electrothermal atomic absorption spectrometry (ET-AAS) using a transversely heated graphite tube atomizer (THGA) with longitudinal Zeeman-effect background correction. The thermal behavior of both analytes during pyrolysis and atomization stages were investigated in 0.028 mol l⁻¹ HNO₃ and in 1+1 v/v diluted wine using mixtures of Pd(NO₃)₂+Mg(NO₃)₂ and NH₄H₂PO₄+Mg(NO₃)₂ as chemical modifiers. With 5 μg Pd+3 μg Mg as the modifiers and a two-step pyrolysis (10 s at 400°C and 10 s at 600°C), the formation of carbonaceous residues inside the atomizer was avoided. For 20 μl of sample (wine+0.056 mol l⁻¹ HNO₃, 1+1, v/v) dispensed into the graphite tube, analytical curves in the 0.10–1.0 μg l⁻¹ Cd and 5.0–50 μg l⁻¹ Pb ranges were established. The characteristic mass was approximately 0.6 pg for Cd and 33 pg for Pb, and the lifetime of the tube was approximately 400 firings. The limits of detection (LOD) based on integrated absorbance (0.03 μg l⁻¹ for Cd, 0.8 μg l⁻¹ for Pb) exceeded the requirements of Brazilian Food Regulations (decree #55871 from Health Department), which establish the maximum permissible level for Cd at 200 μg l⁻¹ and for Pb at 500 μg l⁻¹. The relative standard deviations (n=12) were typically <8% for Cd and <6% for Pb. The recoveries of Cd and Pb added to wine samples varied from 88 to 107% and 93 to 103%, respectively. The accuracy of the direct determination of Cd and Pb was checked for 10 table wines by comparing the results with those obtained for digested wine using single-element ET-AAS, which were in agreement at the 95% confidence level.     

Determination of cadmium in biological and environmental samples by slurry electrothermal atomic absorption spectrometry

The retention of cadmium by the bacteria Escherichia coli and Pseudomonas putida was optimized in order to develop a rapid and selective preconcentration method for cadmium from biological and environmental samples prior to determination by electrothermal atomic absorption spectrometry. Living and lyophilized cells for both bacteria were used, but the method using dead cells shows better analytical capabilities. Cadmium from aqueous solutions is easily retained on the outer membrane of both bacteria in the pH range 4-10, although the selected working pHs for E. coli and P. putida were 5 and 9, respectively. Cadmium retained by the bacteria was dispersed in 3.5 M nitric acid and the slurry was introduced directly into the graphite tube. The best sensitivity and detection limit were obtained for E. coli (0.03 ng ml(-1) and 0.04 ng ml(-1) respectively, in the absence of any chemical modifier). A strong spectral interference from nickel chloride was found and methods to overcome it were developed. The proposed extraction procedure was tested by the determination of cadmium in different standard biological and environmental samples.     

The determination of cadmium in microgram amounts of pancreatic tissue by electrothermal atomic absorption spectometry

Cadmium was determined either by direct insertion of freeze-dried biological samples (1–13 μg) or by injection of 2-μl samples of perifusion medium into the graphite furnace. At 228.8 nm ? 10 fmol of cadmium could be measured. The endogenous cadmium contents in the endocrine and exocrine parts of the pancreas were 8.5 ± 2.0 and 15.1 ± 1.4 μ mol (dry wt.), respectively. A less sensitive wavelength (326.1 nm) was employed for measuring the larger amounts obtained after specimens had been incubated in the presence of cadmium.     

电沉积-钨丝电热原子吸收光谱法测定地质样品中痕量金

以市售幻灯投仪卤钨灯泡钨丝为原子化器的钨丝电热原子吸收光谱分析仪(TC-AAS),功率小、仪器成本低[1,2],如用微型CCD光谱仪作检测系统,可以实现原子吸收光谱仪的小型化,甚至可用于野外现场分析[3,4].     

Ultrasound-assisted emulsification-microextraction combined with flame atomic absorption spectrometry for determination of trace cadmium in water samples

The process of ultrasound-assisted emulsification-microextraction (USAEME) was successfully applied for the first time for the extraction and pre-concentration of trace cadmium from water samples, followed by flame atomic absorption spectrometry (FAAS). In the proposed approach, sodium diethyldithiocarbamate trihydrate solution (NaDDTC·3H₂O) was used as a chelating agent and carbon tetrachloride was selected as extraction solvent. Some effective parameters on the microextraction and the complex formation were selected and optimized. These parameters included extraction solvent type as well as extraction volume, time, temperature, and pH, the amount of the chelating agent, and salt effect. Under optimum conditions, an enrichment factor of 95 was obtained from only 5.0 mL of water sample. The calibration graph was linear in the range of 10-600 μg L⁻¹ with a detection limit of 0.91 μg L⁻¹. The relative standard deviation (R.S.D) for ten replicate measurements of 50 and 500 μg L⁻¹ of cadmium were 2.56 and 1.62%. This proposed method was successfully applied in the analysis of four real environmental water samples and good spiked recoveries over the range of 96.5-101.7% were obtained.     

Sensitive determination of cadmium in water samples by room temperature ionic liquid-based preconcentration and electrothermal atomic absorption spectrometry

A sensitive preconcentration methodology for Cd determination at trace levels in water samples was developed in this work. 1-Butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]) room temperature ionic liquid (RTIL) was successfully used for Cd preconcentration, as cadmium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complex [Cd-5-Br-PADAP]. Subsequently, Cd was back-extracted from the RTIL phase with 500 μL of 0.5 mol L⁻¹ nitric acid and determined by electrothermal atomic absorption spectrometry (ETAAS). A preconcentration factor of 40 was achieved with 20 mL of sample. The limit of detection (LOD) obtained under optimum conditions was 3 ng L⁻¹ and the relative standard deviation (R.S.D.) for 10 replicates at 1 μg L⁻¹ Cd²⁺ concentration level was 3.5%, calculated at peak heights. The calibration graph was linear from concentration levels near the detection limits up to at least 5 μg L⁻¹. A correlation coefficient of 0.9997 was achieved. Validation of the methodology was performed by standard addition method and analysis of certified reference material (CRM). The method was successfully applied to the determination of Cd in river and tap water samples.     

Direct determination of nickel in gas oil by atomic absorption spectrometry with electrothermal atomization

A rapid graphite-furnace atomic absorption procedure with simple dilution of samples was tested for the direct determination of sub-ppm levels of nickel in gas oils. The selection of appropriate graphite-furnace parameters, the type of solvent and organometallic standard, the effect of gas oil concentration in diluted samples, precision, accuracy and detection limit were investigated. Sample dilution was necessary because of high viscosity. Results obtained by standard addition for heavy gas oils were confirmed by a wet-ashing flame atomic absorption procedure. The relative standard deviation (r.s.d.) for consecutive determinations of nickel in gas oil solution containing 19 μg Ni l^?1 was 3.1%, and day-to-day r.s.d. for a reference gas oil sample was 5.3%. Accuracy was determined with an NBS standard reference oil GM-5 (4.6 ± 4.7% relative error in four determinations). Recovery experiments gas 104 ± 12% of the added nickel.     

Determination of nanogram amounts of cadmium in water by electrothermal atomic absorption spectrometry after flotation separation

A method is described for the flotation an determination of ng-levels of cadmium in water. Cadmium in a 1-l sample of water is coprecipitated with hydrated zirconium oxide at pH 9.1 ± 0.1. The precipitate is floated with the aid of a surfactant solution and small air bubbles, separated and dissolved in dilute hydrochloric acid. The cadmium content is determined by electrothermal atomic absorption spectrophotometry. The method is applied to the determination of ng l^?1 levels of cadmium in fresh water. The time required for preconcentration of cadmium from a 1-l sample is 20 min per sample, after 20 min stirring.     

Arsine generation and determination of trace amounts of arsenic by atomic absorption spectrometry

Arsenic can be determined by atomic absorption spectrometry after reduction to arsine with potassium iodide, tin(II) chloride and zinc powder tablet; the arsine generated is carried into an argon-hydrogen flame by means of argon. Accuracy, precision and speed are satisfactory. Serious interferences arise only from nitric acid, lead, chromium and selenium.     

Interference of salts on the determination of lead by electrothermal atomic absorption spectrometry. Ion chromatographic study

The influence of various salts on the atomization signal of lead has been examined by using a transverse heated atomic absorption spectrometer. To get more information about interference mechanisms, volatilization of salts has been studied by ion chromatographic analysis of the residue left on the furnace after drying or charring. The use of a Pd/Mg chemical modifier in these model solutions has also been examined. In 0.1 M chloride medium, NaCl, MgCl₂ and CaCl₂ do not interfere significantly. However, their different behaviour in the furnace, and particularly hydrolysis of MgCl₂ influence greatly the charring curves of Pb. The use of a Pd/Mg modifier appears interesting only in the case of NaCl. Indeed, Pd stabilizes Pb sufficiently to permit the removal of NaCl by charring. In the case of MgCl₂, Pb is not sufficiently stabilized to remove chloride through hydrolysis of MgCl₂ or volatilization of MgCl₂. In the presence of CaCl₂, the Pb signal is delayed and coincides with the background absorption signal of CaCl₂; the stabilization effect is not sufficient to eliminate CaCl₂ by charring before atomization. At 0.1 M nitrate concentration, the presence of NaNO₃, Mg(NO₃)₂, and particularly Ca(NO₃)₂, greatly modifies the atomization signal shape of Pb. Pb is more stabilized in nitrate medium, but losses are observed at the decomposition step of nitrate salts. In this medium, the stabilization effect of Pd leads to a single peak signal and permits elimination of nitrate decomposition products before atomization. Interference effects are more important in the presence of 0.1 M sulphate salts and increase with the acidity of the medium. Na₂SO₄, which is reduced to Na₂S on the graphite, does not interfere significantly. However, the decomposition products of MgSO₄ and CaSO₄ induce an important interference effect on the determination of Pb which is stabilized in the furnace. In the case of Na₂SO₄, the use of the Pd/Mg modifier delays the atomization signal which coincides with the background absorption signal, leading to an important interference effect which cannot be eliminated by charring. In the presence of MgSO₄ and CaSO₄, the stabilizing effect of Pd permits the elimination of decomposition products of sulphate salts before atomization and suppresses the chemical interference effect.