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.     

Rapid determination of lead and cadmium in sewage sludge samples using electrothermal atomic absorption spectrometry with slurry sample introduction

Lead and cadmium concentrations in sewage sludge samples are determined by suspending the ground samples in a solution containing 10% (v/v) concentrated hydrofluoric acid, 1% (v/v) concentrated nitric acid, 0.5% (m/v) dihydrogen ammonium phosphate and 0.1% (m/v) sodium hexametaphosphate. Aliquots of 20 μL of these suspensions (4 mg/mL) are diluted to 1000 μL with the same solution and then injected into the electrothermal atomizer. The drying stage is performed by programming a 400?°C temperature, a ramp time of 20 s and a hold time of 15 s on the power supply of the atomizer. No ashing step is used. Platform atomization is carried out at 1600 and 1800?°C for Pb and Cd, respectively. Calibration is performed using aqueous standards in the 5–75 and 0.2– 5 μg/L Pb and Cd ranges, respectively. Results obtained for three certified reference materials and four samples demonstrate the reliability of the procedures described.     

Rapid determination of lead and cadmium in sewage sludge samples using electrothermal atomic absorption spectrometry with slurry sample introduction

Lead and cadmium concentrations in sewage sludge samples are determined by suspending the ground samples in a solution containing 10% (v/v) concentrated hydrofluoric acid, 1% (v/v) concentrated nitric acid, 0.5% (m/v) dihydrogen ammonium phosphate and 0.1% (m/v) sodium hexametaphosphate. Aliquots of 20 microL of these suspensions (4 mg/mL) are diluted to 1000 microL with the same solution and then injected into the electrothermal atomizer. The drying stage is performed by programming a 400 degrees C temperature, a ramp time of 20 s and a hold time of 15 s on the power supply of the atomizer. No ashing step is used. Platform atomization is carried out at 1600 and 1800 degrees C for Pb and Cd, respectively. Calibration is performed using aqueous standards in the 5-75 and 0.2-5 microg/L Pb and Cd ranges, respectively. Results obtained for three certified reference materials and four samples demonstrate the reliability of the procedures described.     

Rapid determination of lead and cadmium in biological fluids by electrothermal atomic absorption spectrometry using Zeeman correction

Procedures for the electrothermal atomic absorption spectrometric determination of lead and cadmium in urine, serum and blood are developed. For serum and blood, the samples are diluted by incorporating 0.015% (w/v) Triton X-100 and 0.1% (w/v) ammonium dihydrogenphosphate to the solutions, which are then introduced directly into the furnace. A solution containing 15% (w/v) hydrogen peroxide and 0.65% (w/v) nitric acid is also introduced into the atomizer by means of a separate injection. Zeeman-based correction is recommended. Both conventional and fast-heating programs are discussed. Calibration is carried out using the standard additions method. The reliability of the procedures is checked by analyzing three certified reference materials and by recovery studies.     

Rapid determination of lead in water samples by dispersive liquid-liquid microextraction coupled with electrothermal atomic absorption spectrometry

The need for highly reliable methods for the determination of trace and ultratrace elements has been recognized in analytical chemistry and environmental science. A simple and powerful microextraction technique was used for the detection of the lead ultratrace amounts in water samples using the dispersive liquid-liquid microextraction (DLLME), followed by the electrothermal atomic absorption spectrometry (ET AAS). In this microextraction technique, a mixture of 0.50 mL acetone (disperser solvent), containing 35 microL carbon tetrachloride (extraction solvent) and 5 microL diethyldithiophosphoric acid (chelating agent), was rapidly injected by syringe into the 5.00 mL water sample, spiked with lead. In this process, the lead ions reacted with the chelating agent and were extracted into the fine droplets of CCl(4). After centrifugation (2 min at 5000 rpm), the fine CCl4 droplets were sedimented at the bottom of the conical test tube (25+/-1 microL). Then, 20 microL from the sedimented phase, containing the enriched analyte, was determined by ET AAS. The next step was the optimization of various experimental conditions, affecting DLLME, such as the type and the volume of the extraction solvent, the type and the volume of the disperser solvent, the extraction time, the salt effect, pH and the chelating agent amount. Moreover, the effect of the interfering ions on the analytes recovery was also investigated. Under the optimum conditions, the enrichment factor of 150 was obtained from only a 5.00 mL water sample. The calibration graph was linear in the range of 0.05-1 microg L(-1) with the detection limit of 0.02 microg L(-1). The relative standard deviation (R.S.D.) for seven replicate measurements of 0.50 microg L(-1) of lead was 2.5%. The relative lead recoveries in mineral, tap, well and sea water samples at the spiking level of 0.20 and 0.40 microg L(-1) varied from 93.5 to 105.0. The characteristics of the proposed method were compared with the cloud point extraction (CPE), the liquid-liquid extraction, the solid phase extraction (SPE), the on-line solid phase extraction (SPE) and the co-precipitation, based on bibliographic data. The main DLLME advantages combined with ET AAS were simplicity of operation, rapidity, low cost, high-enrichment factor, good repeatability, low consumption of extraction solvent, requiring a low sample volume (5.00 mL).     

Direct determination of cadmium in natural waters by electrothermal atomic absorption spectrometry without matrix modification

A procedure for the determination of cadmium in fresh, coastal and estuarine waters by polarized Zeeman-effect graphite-furnace atomic absorption spectrometry is validated by using lake waters and seawater. The limit of detection for freshwaters is <2 ng l^?1 cadmium. Undiluted seawater can be analyzed directly without the addition of matrix modifiers with the aid of a stabilized temperature platform. The instrument is calibrated with diluted NBS SRM 1643a (Trace Elements in Water). Analytical performance was tested extensively with fresh and brackish water samples and procedures were worked out to ensure that a high degree of accurately is achieved consistently.     

Rapid determination of lead, cadmium and thallium in cements using electrothermal atomic absorption spectrometry with slurry sample introduction

 A method is proposed for the determination of Pb, Cd and Tl in cements by ETAAS. The samples are suspended in a medium containing 10% v/v ethanol and 1% v/v both conc. nitric and hydrofluoric acids and are directly introduced into the electrothermal atomizer. The drying stage is performed by programming a 400 °C temperature, a ramp time of 5 s and a hold time of 30 s on the power supply to the atomizer. No ashing step is used. Atomization is carried out at 2100, 1800 and 1700 °C for Pb, Cd and Tl, respectively. For Cd determination, ammonium dihydrogen phosphate is added to the suspension medium. No modifier other than hydrofluoric acid is required for the Pb and Tl determination. It is shown that the results obtained by using direct calibration with aqueous standards for five commercial samples agree with those found by means of the standard additions method. Received: 29 March 1996/Revised: 24 May 1996/Accepted: 30 May 1996     

Determination of lead in waters by atomic absorption spectrometry with electrothermal atomization

Summary The electrothermal atomization of lead has been investigated for accurate determination of lead in water samples. Thiourea served to lower the atomization temperature of lead and to eliminate the interferences from chloride matrix. The addition of thiourea also allowed the accurate determination of lead irrespective of its chemical form. The absolute sensitivity (1% absorption) was 1.1 × 10^–12g of lead. The method permits the direct rapid determination of lead in water samples including sea water.

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Bestimmung von Blei in Wässern durch Atomabsorptions-Spektrometrie mit elektrothermischer Atomisierung

Zusammenfassung Zur Verringerung der Atomisie-rungstemperatur und zur Beseitigung von Störungen durch die Chloridmatrix wird ein Zusatz von Thioharnstoff empfohlen. Dieser Zusatz gestattet außerdem eine genaue Bestimmung unabhängig von der chemischen Form, in der das Blei vorliegt. Die absolute Empfindlichkeit (1% Absorption) beträgt 1,1 · 10^–12 g Pb. Das Verfahren wurde zur direkten Bleibestimmung in Wässern, einschl. Meereswasser, angewendet.

     

Determination of cadmium, copper, lead and zinc in water samples by flame atomic absorption spectrometry after cloud point extraction

Cloud point extraction (CPE) has been used for the simultaneous pre-concentration of cadmium, copper, lead and zinc after the formation of a complex with 1-(2-thiazolylazo)-2-naphthol (TAN), and later analysis by flame atomic absorption spectrometry (FAAS) using octylphenoxypolyethoxyethanol (Triton X-114) as surfactant. The chemical variables affecting the separation phase and the viscosity affecting the detection process were optimized. At pH 8.6, pre-concentration of only 50 ml of sample in the presence of 0.05% Triton X-114 and 2×10⁻⁵ mol l⁻¹ TAN permitted the detection of 0.099, 0.27, 1.1 and 0.095 ng ml⁻¹ cadmium, copper, lead and zinc, respectively. The enhancement factors were 57.7, 64.3, 55.6 and 63.7 for cadmium, copper, lead and zinc, respectively. The proposed method has been applied to the determination of cadmium, copper, lead and zinc in water samples and a standard reference material (SRM).     

石墨炉原子吸收法快速测定血液中铅和镉

建立了快速测定血液中铅和镉的石墨炉原子吸收光谱法。使用5%硝酸溶液对样品进行脱蛋白处理,然后在旋涡混合器上振摇,离心后取上清液上石墨炉原子吸收进行测定。 结果表明,Pb、Cd工作曲线线性关系良好,相关系数均大于0.9994;方法检出限分别为4.32μg/L和0.27μg/L;Pb的回收率为91.60%～97.31%,镉的回收率为97.04%～98.86%;Pb测定的RSD（n=7）为2.35%,Cd测定的RSD（n=7）为1.53%。冻干牛血铅、镉标准物质GBW09139k和GBW09140k的测定值与参考值吻合。该方法快速准确,精密度、准确度、检出限等测定结果令人满意。可以作为日常血铅、血镉的检测的方法。     

Determination of lead and cadmium in urine by electrothermal atomization atomic absorption spectrometry

The applicability of a DETATA sorbent to the preconcentration of lead and cadmium followed by the determination of these elements in urine using atomic absorption spectrometry with electrothermal atomization was demonstrated. After preconcentration by a factor of 10, the limits of detection were 0.01 and 0.2 μg/L for cadmium and lead, respectively. The accuracy of the results was supported by the analysis of Seronorm Trace Elements Urine (Batch no. 101021).     

Determination of cadmium and lead in biological samples by three ultrasonic-based samples treatment procedures followed by electrothermal atomic absorption spectrometry

The development of 3 different ultrasonic-based sample treatment methods, ultrasonic probe-assisted acid extraction, ultrasonic-assisted acid slurry, and ultrasonic-assisted acid pseudodigestion is presented. These methods were compared for the determination of Cd and Pb by electrothermal atomic absorption spectrometry in biological samples (blood and scalp hair) and validated by using certified materials BCR 397 human hair and BCR 185R bovine liver. The sample amounts chosen to perform the analysis were 100 mg and 0.5 mL for solids (human hair and bovine liver) and blood samples, respectively. An acid digestion induced by microwave energy was used to obtain the total metal concentrations and for comparative purposes. The best results were obtained with the ultrasonic-assisted acid pseudodigestion, with which it was possible to perform accurate and precise determination of the Cd and Pb contents in 2 certified reference materials and biological samples of 50 normal males of ages 25-40 years. The precision of the methods, together with their efficiency, rapidity, low cost, and environmental acceptability, make them good alternatives for the determination of trace metals from biological samples. The precision of the methods for accuracy evaluation, resulting in good agreement according to the t-test for a 95% confidence level, and the relative standard deviations were lower than 10% (n=10) for all determinations.     

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.     

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

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

Trace metal determinations in estuarine waters by electrothermal atomic absorption spectrometry after extraction of dithiocarbamate complexes into freon

Cadmium, copper, iron, lead, nickel and zinc are determined. The dithiocarbamate complexes of the metals are extracted into Freon-TF and back-extracted into dilute nitric acid solution. Portions of the back-extracts are injected into a graphite furnace. The method gives complete separation from the matrix irrespective of salinity. It is therefore useful throughout the full salinity range of an estuary, 0–35‰.The effect of high iron concentrations on the extraction is eliminated by using a mixed acetate buffercomplexing agent solution.     

Dynamic ultrasound-assisted extraction of cadmium and lead from plants prior to electrothermal atomic absorption spectrometry

A dynamic ultrasound-assisted extraction step is proposed for the quantitative extraction of Cd and Pb from plant leaves prior to determination by electrothermal atomic absorption spectrometry (ETAAS). Beech leaves (a certified reference material—CRM 100—where the target analytes were not certified) were used for optimizing the extraction step by a multivariate approach. The samples (0.25 g) were subjected to dynamic ultrasound-assisted extraction with dilute nitric acid as extractant. The method was validated with a certified reference material BCR-062 (olive leaves) where both Cd and Pb are certified. The good agreement between the certified values and those found using the proposed method demonstrates its usefulness. The repeatability was 2.0 and 0.9% and the within-laboratory reproducibility was 7.1 and 2.8% for Cd and Pb, respectively. The precision of the method, together with its efficiency, rapidity, low cost and environmental acceptability makes it a good alternative for the determination of trace metals from plant material.     

Determination of cadmium, chromium, copper and lead in sediments and soil samples by electrothermal atomic absorption spectrometry using zirconium containing chemical modifiers.

A method for direct determination of cadmium, chromium, copper and lead in sediments and soil samples by electrothermal atomic absorption spectrometry using Zr, Ir, etylenediamine acetic acid (EDTA), Zr + EDTA, Ir + EDTA, Zr + Ir and Zr + Ir + EDTA as chemical modifiers in 0.5% (v/v) Triton X-100 plus 0.2% (v/v) nitric acid mixture used as diluent was developed. The effects of mass and mass ratio of modifiers on analytes in sample solutions were studied. The optimum masses and mass ratios of modifiers: 20 microg of Zr, 4 microg of Ir, 100 microg of EDTA and 20 microg of Zr + 4 microg of Ir + 100 microg of EDTA, were used to enhance the analyte signals. Pyrolysis and atomization temperatures, atomization and background absorption profiles, characteristic masses, and detection limits of analytes in samples were compared in the presence or absence of a modifier. The detection limits and characteristic masses of analytes in a 0.5% (m/v) dissolved sample (dilution factor of 200 ml g(-1)) obtained with Zr + Ir + EDTA are 8.0 ng g(-1) and 1.2 pg for Cd, 61 ng g(-1) and 4.3 pg for Cr, 32 ng g(-1) and 23 pg for Cu, and 3.4 ng g(-1) and 19 pg for Pb, respectively. The Zr + Ir + EDTA modifier mixture was found to be preferable for the determination of analytes in sediment and soil-certified and standard reference materials. Depending on the sample type, the percent recoveries of analytes were increased from 81 to 103% by using the proposed modifier mixture; the results obtained are in good agreement with the certified values.     

On the determination of lead in wine by electrothermal atomic absorption spectrometry

The parameters of analytical procedures developed for direct ETAAS determination of Pb in wine are discussed. Atomic absorption spectrometers based on transversal and longitudinal Zeeman effect, wall and integrated platform atomization with two main approaches: (i) measurements in the presence of modifier and (ii) measurements without using any modifier are compared. The optimal temperature programs are defined according to the pre-treatment and atomization curves constructed in the presence of different types of wines. For all investigated instrumental systems, 1:1 dilution of wine sample with 0.2 mol L⁻¹ HNO₃ is recommended. Matrix interferences observed, call for standard addition calibration method for Pb quantification in wines. The detection limit (3σ) achieved for wine diluted in the ratio of 1:1 varied from 0.8 to 1.9 μg L⁻¹ depending on the instrument used. The relative standard deviation for the concentration range of 10 to 80 μg L⁻¹ Pb in wine is typically between 4–8%. The accuracy of the analytical procedures recommended was confirmed by comparing the results obtained with those found for wine samples previously digested with HNO₃-H₂O₂ mixture, by added/found method and by parallel analysis using different instruments. A total of 66 wine samples from different regions of Macedonia were analyzed.      

Simultaneous extraction and determination of traces of lead and arsenic in petrol by electrothermal atomic absorption spectrometry

The lead and arsenic compounds are converted to water-soluble iodides by reaction with a solution of iodine in toluene extraction into dilute nitric acid before determination by graphite-furnace atomic absorption spectrometry against aqueous standards. The method is simple, rapid, accurate and reasonably precise.