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.     

Direct determination of cadmium in biological material using electrothermal atomization atomic absorption spectrometry with a metal tube atomizer and a matrix modifier

A direct determination of cadmium by electrothermal atomization atomic absorption spectrometry with a molybdenum tube atomizer has been investigated. Direct calibration method with cadmium standard solutions and ultrasonic agitation method of a solution including sample powder were used. Sulfur served as a matrix modifier for removal of interferences. Though this direct analytical method for cadmium determination in biological materials had a relatively large standard deviation, the accuracy was similar or superior to those of a sample digestion method and the direct analysis without sulfur. The advantages of this method are its simplicity, low cost, high speed of analysis, and rapid calibration.     

Extraction and atomic absorption spectrometric determination of bismuth with electrothermal atomization

Summary A sensitive method for the extraction and atomic absorption spectrometric measurement with electrothermal atomization has been developed for the determination of bismuth in tea and orchard leaves. Bismuth is extracted into m-xylene as diethyldithiocarbamate complex. 2.5–3.0 l/min of argon flow rate, 650–800° C of ashing temperature and 2,200–2,600° C of atomization temperature were the best experimental conditions. A detection limit of 0.02 ng was obtained with a precision of 2–7% and minimal interference effects.Paper read at the meeting of the Japan Society for Analytical Chemistry, October 1978     

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.     

Use of sodium tungstate as a permanent chemical modifier for slurry sampling electrothermal atomic absorption spectrometric determination of indium in soils

A number of chemical modifiers have been assessed for the direct determination of indium in soils using electrothermal atomic absorption spectrometry and slurry sampling. The best results were obtained when the graphite atomizer was impregnated with sodium tungstate, which acts as a permanent chemical modifier. Slurries were prepared by suspending 100 mg sample in a solution containing 1% (v/v) concentrated nitric acid and 10% (v/v) concentrated hydrofluoric acid and then 15-microL aliquots were directly introduced into the atomizer. Standard indium solutions prepared in the suspension medium in the range 4-80 microg L(-1) indium were used for calibration. The relative standard deviation for ten consecutive measurements of a 40 microg L(-1) indium solution was 2.8%. The limit of detection in soils was 0.1 microg g(-1). The reliability of the procedures was confirmed by analysing two standard reference materials and by using an alternative procedure.     

Appraisal of different electrothermal atomic absorption spectrometric methods for the determination of strontium in biological samples

A comparative study of various potential chemical modifiers (La, Mg, Pd, Ni, Ta, Lu, Sm, Eu, Ho, Er, Tm and Tb) as well as of different background correction procedures (deuterium and Zeeman effect) and atomization techniques (wall and platform) for the direct determination of strontium in biological samples was carried out. Two instruments, one with deuterium and the other with Zeeman effect background corrections have been used to perform the experiments. Although La, Mg, Pd, Ta and Lu had a positive effect, lanthanum alone provided the best performance for the determination of strontium in whole blood, urine and bone digests using wall atomization without deuterium background correction. However, neither chemical modifier produced any significant improvement in sensitivity when Zeeman effect background correction with integrated platform atomization was used. Under the optimized conditions, the characteristic masses were 0.82 and 2.20 pg and the detection limits (3σ) were 0.13 and 0.30 μg l⁻¹ with wall atomization and with Zeeman effect background correction respectively. Recovery studies and analysis of standard reference materials certified for strontium were performed to assess the accuracy. The results for the determination of strontium in real samples with wall atomization and lanthanum as chemical modifier, agreed well with those obtained with Zeeman effect background corrector with a precision typically between 0.5 and 3%. Both procedures can be recommended, and the choice will depend on instrument availability.     

Microwave digestion and matrix separation for the determination of cadmium in urine samples by electrothermal atomization atomic absorption spectrometry using a fast temperature program

 A method is proposed which involves sample pretreatment followed by electrothermal atomic absorption spectrometry (ETAAS) for determination of cadmium in human urine. A microwave digestion system was devised to accommodate double-closed vessels for simultaneous digestion of batches of up to 24 urine samples in about 20 min. After digestion, matrix substances which might interfere were removed using silica-immobilized 8-hydroxyquinoline (I-8HOQ) columns. The analyte adsorbed on the column was then eluted with dilute nitric acid solution and determined by ETAAS using a fast temperature program. Neither ashing steps in the furnace heating program nor use of matrix modifiers was necessary. The accuracy, precision, limit of detection, and sample throughput of the method were evaluated. With meticulous control of systematic errors which may be introduced in the pretreatment procedures, the present method can serve as a reference technique for the analysis of Cd in urine samples. Received: 29 July 1996/Revised: 30 September 1996/Accepted: 13 October 1996     

Microwave digestion and matrix separation for the determination of cadmium in urine samples by electrothermal atomization atomic absorption spectrometry using a fast temperature program

 A method is proposed which involves sample pretreatment followed by electrothermal atomic absorption spectrometry (ETAAS) for determination of cadmium in human urine. A microwave digestion system was devised to accommodate double-closed vessels for simultaneous digestion of batches of up to 24 urine samples in about 20 min. After digestion, matrix substances which might interfere were removed using silica-immobilized 8-hydroxyquinoline (I-8HOQ) columns. The analyte adsorbed on the column was then eluted with dilute nitric acid solution and determined by ETAAS using a fast temperature program. Neither ashing steps in the furnace heating program nor use of matrix modifiers was necessary. The accuracy, precision, limit of detection, and sample throughput of the method were evaluated. With meticulous control of systematic errors which may be introduced in the pretreatment procedures, the present method can serve as a reference technique for the analysis of Cd in urine samples. Received: 29 July 1996/Revised: 30 September 1996/Accepted: 13 October 1996     

Slurry atomization of wheat-milled fractions for electrothermal atomic absorption spectrometric determination of nickel and chromium.

A slurry electrothermal atomic absorption spectrometric technique was used to determine Ni and Cr in wheat flour and its by-products. Slurries (3%, w/v) were prepared in a mixture of 15% HNO3-10% H2O2 as suspended medium. Differences in Ni and Cr contents due to origin and texture of the wheat and to the effects of the milling process were studied. Ni and Cr levels were more markedly influenced by the geographical origin of the wheat than by its texture. Both metals were related to the amount of bran present in each milled fraction and varied over the ranges of 212-298 ng/g (Ni) and 34-85 ng/g (Cr) in flours (with minimal bran contents); 297-460 ng/g (Ni) and 67-118 ng/g (Cr) in shorts; and 424-723 ng/g (Ni) and 106-165 ng/g (Cr) in brans. The Ni and Cr contents were not significantly affected by the technological processes typically performed in a flour-producing factory.     

Silicon determination in milk by electrothermal atomic absorption spectrometry using palladium as chemical modifier

A direct method for silicon determination in milk samples by Electrothermal Atomic Absorption Spectrometry was developed. Palladium was used as chemical modifier at a concentration of 610 mg L(-1); with this modifier, silicon was stable up to 1800 degrees C. The precision and accuracy of the method were investigated. The detection limit was 16.2, 2.7 and 7.2 micro g L(-1) for cows' milk, human milk and infant formula, respectively. The method was applied to silicon determination in 17 infant formula samples, 13 human milk samples and 12 cows' milk samples.     

Rhodium as permanent modifier for atomization of lead from biological fluids using tungsten filament electrothermal atomic absorption spectrometry

Rhodium (Rh) was investigated as a permanent modifier for the atomization of Pb from biological fluids in W-filament atomic absorption spectrometry (AAS). Heating the W-filament with a Rh solution provided a protective coating for subsequent determinations of Pb in blood and urine matrices. The W-filament AAS instrumentation used was based on a prototype design that utilized self-reversal background correction scheme and peak area measurements. We found that Rh not only stabilized Pb during the pyrolysis step, but also facilitated the removal of carbonaceous residues during the cleaning step, requiring much less power than with phosphate modifier. Thus, the filament lifetime was greatly extended to over 300 firings. Periodic reconditioning with Rh was necessary every 30 firings or so. Conditioning the filament with Rh also permitted direct calibration using simple aqueous Pb standards. The method detection limit for blood Pb was approximately 1.5 μg dl⁻¹, similar to that reported previously. Potential interferences from concomitants such as Na, K, Ca and Mg were evaluated. Accuracy was verified using lead reference materials from the National Institute of Standards and Technology and the New York State Department of Health. Blood lead results below 40 μg dl⁻¹ were within ±1 μg dl⁻¹ of certified values, and within ±10% above 40 μg dl⁻¹; within-run precision was ±10% or better. Additional validation was reported using proficiency test materials and human blood specimens. All blood lead results were within the acceptable limits established by regulatory authorities in the US. When measuring Pb in urine, sensitivity was reduced and matrix-matched calibration became necessary. The method of detection limit was 27 μg l⁻¹ for urine Pb. Urine lead results were also validated using an acceptable range comparable to that established for blood lead by US regulatory agencies.     

The atomic absorption spectrometric determination of arsenic and selenium in mineral waters by electrothermal atomization

A procedure for the determination of arsenic and selenium in mineral waters based on electrothermal atomic absorption spectrometry is described. Because of matrix effects and the inadequate detection limits for direct determinations, both elements are separated from the macrocomponents by co-precipitation in hydrated iron(III) oxide. The precipitate is dissolved in 0.2 M sulphuric acid for injection. The detection limits are 0.2 and 0.5 μg l^?1 for arsenic and selenium, respectively.     

Flotation separation and electrothermal atomic absorption spectrometric determination of thallium in wastewater samples

The proposed method is a simple process for the determination of trace amount of thallium(I) in the environmental wastewater samples by electrothermal atomic absorption spectrometry. The wastewater samples were obtained from the environment of a cement plant and subjected to a simple treatment, such as adjusting pH and masking the interfering ions, to prepare for the flotation process in which the thallium(I) content was floated as an ion-association complex using iodide and Rhodamine B at the interface of aqueous/cyclohexane layers. The floated layer was then separated and dissolved in 2 ml of a solution, which was 1% to H2SO4 and 50% to methanol, respectively. Aliquots of 10-microl of this solution were subjected to the graphite furnace to determine the thallium(I) content. The flotation process can be carried in a weak acidic medium in which the interfering effects owing to certain metal ions were eliminated by masking them as neutral citrate chelates. The dynamic range for the determination was found to be 1.0 x 10(-8) - 1.0 x 10(-7) mol l(-1). The RSD was 3.2% and the DL was 2.5 x 10(-9) mol l(-1) (calculated as 3SD of the blank). The reliability of the method is demonstrated by the analysis of a synthetic wastewater in which the recovery was found to be 94%.     

Determination of cadmium in biological samples solubilized with tetramethylammonium hydroxide by electrothermal atomic absorption spectrometry, using ruthenium as permanent modifier

The feasibility of Ru as a permanent modifier for the determination of Cd in biological samples treated with tetramethylammonium hydroxide (TMAH) by ET AAS was investigated. The tube treatment with Ru was carried out only once and lasted for about 300 atomization cycles. The pyrolysis and atomization temperatures, 750 °C and 1300 °C, respectively, were chosen from the temperature curves. The sample dissolution procedure was very simple: a sample aliquot was mixed with a small volume of a 25% m/v TMAH solution, the volume was made up to 50 ml and the mixture was kept at 60 °C for 1 h. Six certified biological reference materials were analyzed and the obtained Cd concentrations are within the 95% confidence interval of the certified values, proving the accuracy of the proposed procedure for a variety of biological samples. The calibration curve, with correlation coefficient higher than 0.99, was established for a working range up to10 μg l⁻¹. The precision was good as demonstrated by relative standard deviations below 3%, except for one sample. The limit of detection (3σ) was 0.05 μg l⁻¹ and the characteristic mass was 1.30 pg, obtained in the presence of the Ru modifier.     

Flotation separation and electrothermal atomic absorption spectrometric determination of lead in water samples

Abstract

The application of macro- and micro-electrodes constructed using the new ionophore were tested in a range of solution compositions reflecting concentrations found in fresh waters, and containing Cl^?, NO₃ ^?, SO₄ ^2-, HCO₃ ^2-, H₄SiO₄ and a natural humic acid. The inhibition of the electrode responses to these ions was quantified using a mixed-solution method by optimising the agreement between the measured potentials and predictions from the Nicolsky-Eisenman equation. In addition, measurements were made in separate solutions of KC1 to enable results to be compared with the literature. Apart from the results obtained for humic acid, mean selectivity coefficients for 16 macro- and 21 micro-electrode experiments are given. The results indicate inhibition of the electrode response to phosphate for all the anions in the concentration ranges of 0.05–1 mM Cl^?, 0.1–1.0 mM NO₃ ^?, 0.1–10.0 mM HCO₃ ^? and 0.1–1.5 mM SO₄ ^2- with high selectivity for HPO₄ ^2- in the presence of both dissolved silicon and a standard humic acid. This means that the application of the electrodes to hard waters is impracticable although studies of soft waters and laboratory studies in controlled conditions, e.g. calcium phosphate precipitation experiments, are feasible.     

Electrothermal atomic absorption spectrometric determination of cadmium in environmental samples with niobium wire preconcentration method

A preconcentration method by adsorption of cadmium on a niobium wire was developed for the environmental waters, followed by electrothermal atomic absorption spectrometry with a tungsten tube atomizer. After the preconcentration, the niobium wire was directly inserted into the tungsten tube atomizer. In the preconcentration (adsorption) process of cadmium, the optimal immersing time was 60?s. The effects of large amounts of concomitants on the preconcentration of cadmium were evaluated. When 10³–10⁴ fold excess of matrix elements existed in aqueous solution at pH 4 and 9, the cadmium response was profoundly affected by the matrix elements. However, the cadmium absorption signal was not significantly influenced at pH 7. Therefore, pH 7 was selected for the application into the real environmental samples. Under the optimal conditions, the detection limit (3S/N) for cadmium by the niobium wire preconcentration method was 7.0?pg?mL^?1 and the relative standard deviation was 6.8%. The method with preconcentration on a niobium wire was applied to the determination of cadmium in water and proved to be sensitive, simple and convenient. Because this preconcentration method can be utilized in the in situ treatment of trace cadmium in environmental water samples, it was unnecessary to carry the water samples to the analytical work place. The technique was shown to be useful for the determination of cadmium in environmental water samples at 0.1–1?µg?L^?1 levels.     

Direct determination of cadmium in calcium drug samples using electrothermal atomic absorption spectrometry with a metal tube atomizer and thiourea as a matrix modifier

A laboratory constructed molybdenum tube atomizer was used for direct determination of trace cadmium in drug samples by the electrothermal atomic absorption spectrometric (ETAAS) method. An ultrasonic agitation method for a solution including the sample powder was used. A calibration curve was constructed with a cadmium standard solution including matrix. To eliminate interference from other matrix elements, a chemical modifier thiourea, was used. The detection limit were 17 pg ml(-1) (3 S/N), and the RSD of the direct analysis was 5-17%. The results for cadmium in the four drug samples analysed by the direct ETAAS method matched well with those obtained with nitric acid digested samples. The recovery of added cadmium was 103-106%. An accurate method is elaborated for the determination of cadmium in drug samples by direct ETAAS techniques. The merits of this method are rapid calibration, simplicity, fast analysis, and low cost.     

Evaluation of ion imprinted polymers for the solid phase extraction and electrothermal atomic absorption spectrometric determination of palladium in environmental samples

The complexes of Pd(II) with ammonium pyrrolidinedithiocarbamate (APDC), N,N′-diethylthiourea (DET) and dimethylglyoxime (DMG) were prepared and imprinted into a polymeric network. The ion-imprinted polymers (IIPs) were synthesized by copolymerization of 4-vinylpyridine (VP) and styrene as functional monomers and divinylbenzene as a cross-linking agent in the presence of 2,2-azo-bis-isobutyronitrile as an initiator. The influence of sample volume, pH and flow rate on the extraction efficiency of Pd was studied under dynamic conditions. Pd(II) could be quantitatively retained on each of the studied sorbents at the pH range of 0.5 to 1.0, and eluted with an acidic solution of thiourea. The polymer with the imprinted Pd-DET-VP complex offered the highest selectivity for Pd(II) over certain matrix components, such as Pt(IV), Ni(II) and Cu(II). The low sample pH is an important advantage of the separation procedure, as it allows an effective separation of Pd(II) from complex environmental matrices. The developed separation method was successfully applied to the electrothermal atomic absorption spectrometric (ETAAS) determination of trace amounts of Pd in tap and river water, grass, and certified platinum ore (CRM SARM 7 and SARM 76) samples with reproducibility below 6.5%. The detection limit for Pd(II) obtained by ETAAS after the pre-concentration on Pd-DET-VP polymer was 0.012?ng?mL^?1 for 75?mL sample volume.     

Effectiveness of palladium as a chemical modifier for direct silver and manganese determination in cocaine and heroin by electrothermal atomic absorption spectrometry

Methods for the direct determination of silver and manganese in cocaine and heroin by electrothermal atomic absorption spectrometry using palladium as chemical modifier have been developed. Cocaine samples, 0.5 g, were dissolved in 2 ml of 35.0% (m/v), HNO(3) diluting to 10 ml with ultrapure water. A comparative study of palladium, magnesium nitrate, palladium-magnesium nitrate and nitric acid used as chemical modifiers was carried out, and it was found that palladium alone is adequate to stabilize silver and manganese at charring temperatures of 1000 and 1300 degrees C respectively. A study was made on the insertion of a cooling step before the atomization step, and this approach was not advantageous. Limits of detection of 2.3 and 6.9 microg kg(-1) were obtained for silver and manganese respectively. The analytical recovery oscillated between 95.9 and 103.6% for silver and between 99.7 and 103.0% for manganese. Finally, a study of some interferences and a study of the precision and analytical recovery of the amount of sample were also carried out.     

Direct electrothermal atomic absorption spectrometric determination of selenium in serum

The effect of copper, iron, nickel and silver ions on the thermal stability of inorganic and metabolized forms of selenium in serum was studied with radioactive ⁷⁵Se. Copper and iron had no stabilizing effect but in the presence of nickel or silver the temperature could be raised to 1050°C or 1250°C, respectively, without loss of selenium. On this basis an electrothermal atomic absorption spectrometric method was developed for the direct determination of selenium in human serum; selenium is stabilized with nickel during ashing. In 12 samples of sera from unexposed individuals, the concentrations ranged from 92 pob to 140 ppb. The relative standard deviation of the method is 4%, and the detection limit is 5 ppb.