Cation-exchange separation of metals in dimethyl sulphoxide-aqueous hydrochloric acid media

The behaviour of bismuth, cadmium, copper, lead, silver, tin and zinc on a cation-exchange resin in a solvent system consisting of dimethyl sulphoxide, hydrochloric acid and water was studied. The distribution coefficients of these metal ions between liquid and resin were determined as functions of the concentration of dimethyl sulphoxide and of hydrochloric acid. On the basis of the distribution coefficients found, predictions were made as to the possibilities of separating these metals from mixtures. Such separations were confirmed experimentally for bismuth from lead, bismuth from copper, zinc from lead, lead from cadmium, silver from copper, silver from lead, lead from cadmium from zinc, bismuth from lead from zinc, and bismuth from zinc from copper.     

Systematic Errors in the Determination of Trace Metals by GFAAS Technique,Part I

The behaviour of solutions containing 7 metals in trace range (pH=2) prepared in borosilicate glass and polyethylene containers and transferred into commercial polyethylene–polypropylene and home-made quartz autosampler cups for measurements were studied using graphite furnace atomic absorption spectrometry. The different interactions between metal solution and vessel material were observed for the metals studied. The most significant losses of chromium and nickel occurred on a polyethylene surface, while the highest absorbance signals were registered from quartz containers. Higher absorbance signals from quartz containers were also obtained for cadmium and copper solutions. Contrary to these results, the absorbance signals for lead solutions were lowest when measured from quartz vessels. The container material had no influence on the analytical signals of cobalt and manganese.Received January 15, 2003; accepted April 15, 2003 published online August 22, 2003     

Reduction des interferences sur la determination des metaux lourds dans les sediments de cours d'eau et les boues de stations d'epuration par spectrometrie d'absorption atomique en four graphite

(Reduction of interferences in the determination of trace heavy metals in river sediments and sewage sludges by electrothermal atomic absorption spectrometry.)The interferences of synthetic matrices of river sediments and sewage sludges in the determination of lead, copper, cadmium, chromium and nickel by electrothermal atomic absorption spectrometry were studied; Pb, Cd and Ni were the most sensitive to interferences. The effects of hydrochloric, nitric, perchloric and hydrofluoric acids were tested; perchloric acid was found to interfere most during the determinations. Hydrofluoric acid must be eliminated by evaporation. Techniques for reducing chemical interferences were evaluated. The best method was found to be matrix modification with ammonium dihydrogenphosphate and ascorbic acid for the determination of lead and nickel, and rapid heating (Max Power) for the determination of cadmium. Determinants of copper and chromium were less prone to interference.     

Application of a poly(dithiocarbamate) resin with macroreticular support to the determination of trace amounts of cadmium and lead in non-saline waters.

The chelating poly(dithiocarbamate) resin with macroreticular support is shown to be effective for the preconcentration of cadmium and lead from non-saline waters. The retained ions can be eluted efficiently in 5 ml of 8 mol dm-3 nitric acid from 1-20 cm columns of resin. Poly(dithiocarbamate) resin is used for preconcentration in the determination of cadmium and lead by flame atomic absorption spectrometry. The common ions present in non-saline waters do not interfere. The sensitivity was 0.10 micrograms l-1 of Cd and 0.73 micrograms l-1 of Pb. The detection limits were 0.03 and 0.34 micrograms l-1 for Cd and Pb, respectively. The cadmium and lead concentration rages, determined in mineral and tap waters, were between 0.1 and 0.8 micrograms l-1 and between 0.7 and 16.9 micrograms l-1, respectively.     

A Study of Nafion‐Coated Bismuth‐Film Electrode for the Determination of Zinc,Lead, and Cadmium in Blood Samples

In this article a sensitive differential pulse stripping voltammetry technique on Nafion‐coated bismuth‐film electrode (NCBFE) was studied for the simultaneous determination of zinc, cadmium, and lead ions in blood samples at ultra trace levels. The measurement results were in excellent agreement with those obtained from atomic absorption spectroscopy. Various operational parameters were investigated and discussed in terms of their effect on the measurement signals. Under optimal conditions, calibration curves for the simultaneous determination of zinc, cadmium, and lead ions were achieved, based on three times the standard deviation of the baseline, the limits of detection were 0.09 μg L^?1 for Cd(II), 0.13 μg L^?1 for Pb(II), and 0.97 μg L^?1 for Zn(II) respectively.     

Improvement of the detection power in electrothermal atomic absorption spectrometry by summation of signals : Determination of Traces of Metals in Drinking Water and Urine

In electrothermal atomic absorption spectrometry, the signals corresponding to total absorption (TA), background(BG) adn the required atomic absorption signal (TA - BG) show good temporal reproducibility. For improvement of the detection power, the time-resolved signals can be summed with the aid of a microcomputer. The summed signal height is exponentially related to the number (N) of measurements up to N = 40. The detection power is improved according to the N^{$\text{sol1}\text{2}$} law with a practical limit at summation of ca. 20 signals. Concentrations which are around the detection limit in single measurements (lead and cadmium in drinking water or lead in urine) can readily be determined by summation of signals from, for example, sixteen 20-μl injections of urine. Resulting high summed backgrounds, giving absorbances > 5, can be compensated.     

Determination of cadmium and lead in table salt by sequential multi-element flame atomic absorption spectrometry

In the present paper, a simultaneous pre-concentration procedure for the sequential determination of cadmium and lead in table salt samples using flame atomic absorption spectrometry is proposed. This method is based on the liquid-liquid extraction of cadmium(II) and lead(II) ions as dithizone complexes and direct aspiration of the organic phase for the spectrometer. The sequential determination of cadmium and lead is possible using a computer program. The optimization step was performed by a two-level fractional factorial design involving the variables: pH, dithizone mass, shaking time after addition of dithizone and shaking time after addition of solvent. In the studied levels these variables are not significant. The experimental conditions established propose a sample volume of 250 mL and the extraction process using 4.0 mL of methyl isobutyl ketone. This way, the procedure allows determination of cadmium and lead in table salt samples with a pre-concentration factor higher than 80, and detection limits of 0.3 ng g⁻¹ for cadmium and 4.2 ng g⁻¹ for lead. The precision expressed as relative standard deviation (n = 10) were 5.6 and 2.6% for cadmium concentration of 2 and 20 ng g⁻¹, respectively, and of 3.2 and 1.1% for lead concentration of 20 and 200 ng g⁻¹, respectively. Recoveries of cadmium and lead in several samples, measured by standard addition technique, proved also that this procedure is not affected by the matrix and can be applied satisfactorily for the determination of cadmium and lead in saline samples. The method was applied for the evaluation of the concentration of cadmium and lead in table salt samples consumed in Salvador City, Bahia, Brazil.     

Determination of Cadmium and Lead in Human Teeth Samples Using Dispersive Liquid‐liquid Microextraction and Graphite Furnace Atomic Absorption Spectrometry

A new method for the determination of cadmium and lead in human teeth was developed based on dispersive liquid‐liquid microextraction preconcentration and graphite furnace atomic absorption spectrometry determination. In the proposed approach, O,O‐diethyldithiophosphate (DDTP) was used as a chelating agent, and carbon tetrachloride and methanol were selected as extraction and dispersive solvents. Some factors influencing the extraction efficiency of cadmium and lead and their subsequent determination, including extraction and dispersive solvent type and volume, pH of sample solution, concentration of the chelating agent and extraction time, were studied and optimized. Under the optimum conditions, the enrichment factor of 116 and 68 for cadmium and lead were achieved. The detection limit for cadmium and lead was 5.6 and 45 ng L^?1, and the relative standard deviation (R.S.D) was 4.5% and 3.8% (n = 7, c = 1.0 ng mL^?1), respectively. Verification of the accuracy of the method was carried out by analysis of a standard reference material (NIST 1486, bone meal). The method was successfully applied to the determination of trace amount of cadmium and lead in human teeth samples with satisfactory results.     

Effect of Organic Substances on the Results of Anodic Stripping Voltammetry Detection of Metal Ions in Aqueous Media

Abstract

The d.c. anodic stripping voltammetry method has been used to investigate the effect of organic substances simulating the composition of natural waters on the results of determination of concentration levels of copper, lead and cadmium. The response, sensitivity and concentration (the latter determined by the standard additions method) have been used as sources of information. In the presence of enzymes, fulvic acids, humic acids and polyethylene glycol all these three parameters change in the case of determination of copper and lead, making the results unreliable. The determination of cadmium concentration is not hampered by the said organic substances.     

Determination of cadmium in orthophosphoric acid by graphite furnace atomic absorption spectrometry

Summary Cadmium has been determined in analytical-reagent grade orthophosphoric acids by direct graphite furnace atomic absorption spectrometry with Zeeman background correction. The detection limit was 3.0 pg cadmium, corresponding to 1.0 g/l of cadmium in the concentrated acid. Most of the acids analyzed contained 2–5 g/l of cadmium. The method was checked using electrochemical preconcentration of cadmium, followed by flame atomic absorption spectrometry.     

Synergic extraction of zinc, cadmium and lead with hexafluoroacetylacetone and di-n-butylsulphoxide and tri-n-butyl phosphate, and the gas chromatography of the zinc adduct

The synergic solvent extraction of zinc(II), cadmium(II), and lead(II) with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, H(HFA), and tri-n-butyl phosphate (TBP) or di-n-butylsulphoxide (DBSO) as neutral donors, into cyclohexane has been investigated. Quantitative extraction occurs at pH 4.5-6.0 in extraction times of 10-30 min, depending on the metal species. The optimum pH, equilibration time, stoichiometry and stability of the extracted species, as well as the effect of fluorinated beta-diketone concentration, metal concentration and neutral donor concentration on the extraction are reported. The extracted species was found to be M(HFA)(2).2DBSO or M(HFA)(2).2TBP by mass-action studies. Thermogravimetric analysis of the complexes is reported. The gas chromatographic behaviour of the ternary complexes of the three metals has also been studied. A calibration plot of peak area vs. the amount of zinc injected was linear over the range 40-900 ng of zinc for the Zn(HFA)(2). 2DBSO species; the cadmium and lead species apparently decomposed on the column and useful chromatographic peaks were not observed. The calibration plot for zinc was determined on the basis of the averages of 3-5 replicate determinations for 14 different concentrations over the range stated. The average relative standard deviation was 2.9%.     

Preconcentration of Cadmium with OP-10 Nonionic Surfactant Phases at the Cloud Point

The effect of the main parameters on the extraction of cadmium with carboxylic acids into the micellar phase of the OP-10 nonionic surfactant at the cloud point was studied. Conditions were found for the atomic absorption determination of cadmium in natural and waste waters using the micellar-extraction preconcentration with capric acid and n-octylamine into the surfactant phase.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 5, 2005, pp. 458–462.Original Russian Text Copyright © 2005 by Doroshchuk, Kulichenko.     

Rapid coprecipitation-separation and flame atomic absorption spectrometric determination of lead and cadmium in water with cobalt (II) and ammonium pyrrolidine dithiocarbamate

A coprecipitation technique which does not require complete collection of the precipitate was proposed for the determination of trace lead and cadmium in water with flame atomic absorption spectrometry (FAAS) after preconcentration of lead and cadmium by using cobalt (II) and ammonium pyrrolidine dithiocarbamate (Co-APDC) as coprecipitant and known amount of cobalt as an internal standard. Since lead, cadmium and cobalt were well distributed in the homogeneous precipitate, the concentration ratio of lead to cobalt, and cadmium to cobalt remained unchanged in any part of the precipitate. The amount of lead and cadmium in the original sample solution can be calculated respectively from the ratio of the absorbance values of lead and cadmium to cobalt in the final sample solution that is measured by FAAS and the known amount of the lead and cadmium in the standard series solutions. The optimum pH range for quantitative coprecipitation of lead and cadmium is from 3.0 to 4.5. The 16 diverse ions tested gave no significant interferences in the lead and cadmium determination. Under optimised conditions, lead ranging from 0 to 40?µg and cadmium ranging from 0 to 8?µg were quantitatively coprecipitated with Co-APDC from 100?mL sample solution (pH?～?3.5). This coprecipitation technique coupled with FAAS was applied to the determination of lead and cadmium in water samples with satisfactory results (recoveries in the range of 94.0–108%, relative standard deviations <6.0%).     

Phase diagrams and optical properties of binary liquid-crystal systems of cobalt(II) caprylate with a divalent metal caprylate

Phase equilibria in the binary systems of cobalt(II) caprylate with a divalent metal (lead, cadmium, or zinc) caprylate were studied by differential thermal analysis and polarization microscopy, and the concentration and temperature ranges of the existence of liquid crystals and glasses were determined. Continuous or boundary smectic liquid-crystal solutions were found to form in all the systems. The temperature and concentration dependences of the electronic absorption spectra of liquid crystals and glasses in binary systems based on cobalt caprylate were investigated.     

原子吸收光谱法测定茶叶中铅和镉时消解方法的优化

采用多种方法对同一种茶叶进行消解,用原子吸收光谱法测定不同方法消解的茶叶中有害微量元素铅和镉的含量并进行对比,探索了茶叶中微量元素铅和镉低损耗的最佳消解条件.实验结果表明,不同的消解方式对茶叶中微量元素的测定结果影响很大.测定茶叶中铅和镉元素时,采用硝酸-高氯酸加盖浸泡过夜方法较为理想.     

Cloud point extraction for the determination of cadmium and lead employing sequential multi-element flame atomic absorption spectrometry

A cloud point extraction procedure for pre-concentration and determination of cadmium and lead in drinking water using sequential multi-element flame atomic absorption spectrometry is described. 4-(2-thiazolylazo)-orcinol (TAO) has been used as complexing agent and the micellar phase was obtained using the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) and centrifugation. The conditions for reaction and extraction (surfactant concentration, reagent concentration, effect of incubation time, etc) were studied and the analytical characteristics of the method were determined. The method allows the determination of cadmium and lead with quantification limits of 0.30?µg?L^?1 and 2.6?µg?L^?1, respectively. A precision expressed as relative standard deviation (RSD, n?=?10) of 2.3% and 2.6% has been obtained for cadmium concentrations of 10?µg?L^?1 and 30?µg?L^?1, respectively, and RSD of 1.3% and 1.7% for lead concentrations of 10?µg?L^?1 and 30?µg?L^?1, respectively. The accuracy was confirmed by analysis of a natural water certified reference material. The method has been applied for the determination of cadmium and lead in drinking water samples collected in the cities of Ilhéus and Itabuna, Brazil. Recovery tests have also been performed for some samples, and results varied from 96 to 105% for cadmium and 97 to 106% for lead. The cadmium and lead concentrations found in these samples were always lower than the permissible maximum levels stipulated by World Health Organization and the Brazilian Government.     

Determination of trace metals by anodic stripping voltammetry using a bismuth-modified carbon nanotube electrode

A bismuth-modified carbon nanotube electrode (Bi-CNT electrode) was employed for the determination of trace lead, cadmium and zinc. Bismuth film was prepared by in situ plating of bismuth onto the screen-printed CNT electrode. Operational parameters such as preconcentration potential, bismuth concentration, preconcentration time and rotation speed during preconcentration were optimized for the purpose of determining trace metals in 0.1M acetate buffer solution (pH 4.5). The simultaneous determination of lead, cadmium and zinc was performed by square wave anodic stripping voltammetry. The Bi-CNT electrode presented well-defined, reproducible and sharp stripping signals. The peak current response increased linearly with the metal concentration in a range of 2-100 microg/L. The limit of detection was 1.3 microg/L for lead, 0.7 microg/L for cadmium and 12 microg/L for zinc (S/N=3). The Bi-CNT electrode was successfully applicable to analysis of trace metals in real environments.     

15种中成药中有害重金属铅、镉、铜含量的测定

为了解中药重金属污染情况,测定了市售常用15种中成药中重金属铅、镉、铜的含量,其中铅、镉采用石墨炉原子吸收法,铜采用火焰原子吸收法测定.结果表明,15种中成药均不同程度被这3种重金属污染,通心络中铅、镉、铜含量都已超标,桑菊感冒片镉超标,中药重金属污染问题仍然存在.     

The electrical conductance of some molten car☐ylate mixtures

Data are presented for the electrical conductivities in the melt for lead(II) octadecanoate/lead(II) decanoate, lead(II) hexadecanoate/lead(II) decanoate, lead(II) hexadecanoate/zinc hexadecanoate and lead(II) hexadecanoate/cadmium hexadecanoate mixtures over their complete composition ranges. The electrical conductivities are measured as a function of temperature from just above the melting point to just below the decomposition point of the mixtures. The Arrhenius plots for the mixtures are linear in all cases and the activation energies are determined. While the activation energies for lead(II) octadecanoate/lead(II) decanoate and lead(II) hexadecanoate/lead(II) decanoate mixtures are mole fraction independent over the concentration range studied, rendering support to previous models advanced by other workers that the major charge carrier is the free metal cation, the other systems show no such simple behaviour. In these systems there are indications of deviations from ideal behaviour, suggesting that entropy and enthalpy of mixing might be important.     

Simultaneous determination of cadmium and lead in urine by means of computerized potentiometric stripping analysis

In computerized potentiometric stripping analysis for cadmium and lead in urine the samples are acidified with hydrochloric acid to a total concentration equal to 0.5 M. The sample is pre-electrolyzed at —1.25 V vs. SCE for 2 min without prior sample heating or deoxygenation, the working electrode being a mercury pre-coated glassy-carbon electrode. The lead and cadmium concentrations are evaluated by means of standard addition. Detection limits are 1 nM for both elements. Results obtained by potentiometric stripping analysis and by solvent extraction/atomic absorption are compared for samples from unexposed persons and from one patient under penicillamine treatment. The relative merits of the potentiometric stripping, anodic stripping and atomic absorption techniques are discussed.