Differential pulse polarographic determination of trace amounts of vanadium and molybdenum in various standard alloys and environmental samples after preconcentration of their morpholine-4-carbodithioates on microcrystalline naphthalene or morpholine-4-dithiocarbamate cetyltrimethyl-ammonium bromide-naphthalene adsorbent

A highly selective, sensitive, and fairly rapid and economical differential pulse polarographic (DPP) method has been reported for the determination of trace amounts of vanadium and molybdenum in standard alloys and various environmental samples. The morpholine-4-carbodithioates of these metals were retained (>99% recovery) quantitatively on microcrystalline naphthalene in the pH range 4.5-6.9 for vanadium and 1.5-4.5 for molybdenum. These metals were determined by DPP after desorption with 10 ml of 1 M HCl. Vanadium and molybdenum may also be preconcentrated by passing their aqueous solutions under similar conditions on morpholine-4-dithiocarbamate CTMAB-naphthalene adsorbent packed in a column at a flow rate of 1-5 ml min(-1) and determined similarly. The detection limits are 0.20 ppm for vanadium and 0.04 ppm for molybdenum at minimum instrumental settings (signal to noise ratio=2). The linearity is maintained in the following concentration ranges, vanadium 0.50-10.0 and molybdenum 0.10-9.0 ppm, with a correlation factor of 0.9996 (confidence interval of 95%, slopes 0.0196 and 0.01497 muA mug(-1), intercepts 3.65x10(-3) and -1.92x10(-3) respectively) and relative standard deviation of 1.1% in the microcrystalline method, while in the column method, the linearity is maintained in the concentration ranges, 0.50-6.5 for vanadium and 0.10-5.5 ppm for molybdenum with correlation factor of 0.9994 (with confidence interval of 95%, slopes 0.0194, 0.015 muA mug(-1), intercepts 3.60x10(-3) and -1.90x10(-3) respectively) and relative standard deviation of 1.4%. Various parameters such as the effect of pH, reagent, naphthalene and CTMAB concentrations, volume of aqueous phase and interference of a large number of metal ions on the estimation of vanadium and molybdenum have been studied in detail to optimize the conditions for their voltammetric determination at trace level in various standard alloys and environmental samples.     

Spectrophotometric determination of zinc, cadmium, and lead after extraction of their morpholine-4-carbodithioates into molten naphthalene and replacement by copper

Zinc, cadmium, and lead react quantitatively in the pH ranges of 3.9–9.2, 3.5–11.2, and 5.5–10.5, respectively, to form water insoluble and thermally stable complexes which are easily extracted into molten naphthalene. The solid naphthalene containing the colorless complex is dissolved in chloroform and then replaced by copper to develop a yellow color in the chloroform layer. The absorbance in each case is measured at 435 nm against reagent blank. Beer's law holds over the concentration ranges of 3.5–95.0, 3.0–105.0, and 8.5–125. 0 μg for zinc, cadmium, and lead, respectively, into 10 ml of the chloroform solution. The molar absorptivities are calculated to be Zn, 1.048 × 10⁴ liters mol⁻¹ cm⁻¹; Cd, 1.054 × 10⁴ liters mol⁻¹ cm⁻¹, and Pb, 1.014 × 10⁴ liters mol⁻¹ cm⁻¹ with sensitivities in terms of Sandell's definition of 0.0062 μg Zn/cm², 0.010 μg Cd/cm², and 0.020 μg Pb/cm², respectively. Ten replicate determinations of sample solutions containing 30 μg of zinc, 18.7 μg of cadmium, and 42.5 μg of lead give mean absorbances 0.480, 0.175, and 0.208 with standard deviations of 0.0017, 0.0013, and 0.0015 or relative standard deviations of 0.35, 0.74, and 0.72%, respectively. The interference of various ions has been studied and the method has been applied to the determination of cadmium in various synthetic mixtures and zinc and lead in some standard reference materials.     

Simultaneous determination of selenium and lead in whole blood samples by differential pulse polarography

The polarographic reduction of lead in the presence of selenite gives rise to an additional peak corresponding to the reduction of lead (Pb) on adsorbed selenium (Se) on mercury at −0.33 V. The selenium and lead content can be determined using this peak by the addition of a known amount of one of these ions first and then the second ion. The linear domain range of lead is 5.0×10⁻⁷–2.0×10⁻⁵ M and for selenium 5.0×10⁻⁷–1.0×10⁻⁵ M. Using this method 4.90×10⁻⁷ M Se(IV) and 1.47×10⁻⁶ M Pb(II) in a synthetic sample could be determined with a relative error of +2.0% and 1.8%, respectively (n=4). A recovery test after acid digestion for a synthetic sample was 97% for selenium and 96.5% for lead. The method was applied to 1 ml of digested blood, and 328±23 μg l⁻¹ Se(IV) and 850±62 μg l⁻¹ Pb(II) could be determined with a 90% (n=5) confidence interval.     

Differential pulse polarographic determination of lead in complex materials after adsorption of its N-methylethylxanthocarbamate complex on microcrystalline naphthalene or on N-methylethylxanthocarbamate-benzyldimethyltetradecylammonium-naphthalene adsorbent

Lead is quantitatively adsorbed as the lead N-methylethylxanthocarbamate (MEXC)-benzyldimethyltetradecylammonium (BDTA) ion pair complex on microcrystalline naphthalene in the pH range 4.0-11.0. The metal is desorbed with HCI and determined by differential pulse polarography. Alternatively lead can be quantitatively adsorbed on the adsorbent (MEXC-BDTA-naphthalene) packed in a column at a flow rate of 1-2 mL/min and determined similarly. Dissolved oxygen is removed by adding a few milliliters of 4% NaBH4 solution. The detection limit is 0.12 microg/mL at the minimum instrumental settings (signal-to-noise ratio, 2). Linearity was obtained over the concentration range 0.3-20.0 microg/mL with a correlation factor of 0.9998 and a relative standard deviation of +/- 0.98%. Various parameters, such as the effect of pH, volume of aqueous phase, flow rate, and the interference of a large number of metal ions and anions, were studied in detail to optimize the conditions for the trace determination of lead in various standard alloys, standard biological materials, and environmental samples.     

Differential pulse polarographic determination of tin in alloys and environmental samples after preconcentration with the ion pair of 2-nitroso-1-naphthol-4-sulfonic acid and tetradecyldimethylbenzylammonium chloride onto microcrystalline naphthalene or by column method

A highly selective, sensitive, rapid and economical differential pulse polarographic method has been developed for the determination of trace amount of tin in various standard alloys and environmental samples after adsorption of its 2-nitroso-1-naphthol-4-sulfonic acid-tetradecyldimethylbenzylammonium chloride on microcrystalline naphthalene in the pH range of 8.7-10.6. After filtration, the solid mass is shaken with 8-10 ml of 3.5 M hydrochloric acid and tin is determined by differential pulse polarography (DPP). Tin can alternatively be quantitatively adsorbed on 2-nitroso-1-naphthol-4-sulfonic acid-tetradecyldimethylbenzylammonium-naphthalene adsorbent packed in a column and determined similarly. The detection limit is 0.15 mug ml(-1) (signal to noise ratio=2) and the linearity is maintained in the concentration range 0.5-220 mug ml(-1) with a correlation coefficient of 0.9995 and relative standard deviation of +/-0.88%. Characterization of the electroactive process included an examination of the degree of reversibility. Various parameters such as the effect of pH, volume of aqueous phase and interference of a number of metal ions on the determination of tin has been studied in detail to optimize the conditions for determination in standard alloys and environmental samples.     

Simultaneous determination of the isomers of nitrophthalic acid by differential pulse polarography

A differential pulse polarographic method has been developed for simulataneous determination of isomers of nitrophthalic acid. In ammonia buffer (1.0 M), the peak potentials for the reduction of 4-and 3-nitrophthalic acids are ?0.54 and 0.67 V vs. SCE, respectively. Response of peak current vs. concentration of each isomer is linear over three orders of magnitude change in concentration. The detection limit for both 4-and 3-nitrophthalic acid is 0.2 mg l^?1. A typical sample can be analyzed for both isomers of nitrophthalic acid in less than 15 min.     

Differential pulse polarography determination of indium after column preconcentration with [1-(2-pyridylazo)-2-naphthol]-naphthalene adsorbent or its complex on microcrystalline naphthalene

A highly selective, sensitive and economical differential pulse polarographic method has been developed for the determination of trace amount of indium in various samples after adsorption of its 1-(2-pyridylazo)-2-naphthol on naphthalene in the pH range of 6.5-11.5. After filtration, the solid mass is shaken with 8 ml of 1 M hydrochloric acid and indium is determined by differential pulse polarography (DDP). Indium can alternatively be quantitatively adsorbed on [1-(2-pyridylazo)-2-naphthol]-naphthalene adsorbent packed in a column and determined similarly. The detection limit is 0.2 ppm (signal to noise ratio=2) and the linearity is maintained in the concentration range 0.8-125 ppm with a correlation coefficient of 0.9994 and relative standard deviation of +/-0.96%. Characterization of the electroactive process included an examination of the degree of reversibility. Various parameters such as the effect of pH, volume of aqueous phase and interference of a number of metal ions on the determination of indium have been studied in detail to optimize the conditions for determination in various samples.     

The determination of a carbamate insecticide in soil samples by differential pulse polarography

Differential pulse polarography is shown to be a simple and potentially useful method for monitoring the degradation of a carbamate insecticide (Bendiocarb; 2,3-isopropyli-denedioxyphenyl-N-methylcarbamate) in soil samples. Only extraction from the soil sample with dichloromethane and evaporation of the extract is needed prior to polarography. Calibration plots were linear over the range 10–50 mg l^?1 at ?0.94 V vs. Ag/AgCl in an acetate buffer of pH 5.0. There is no apparent interference from hydrolysis products or soil components.     

Wide linear range nanomaterial/ionophore-based electrode used for determination of lead in environmental and biological samples with differential pulse voltammetry

A new chemically modified carbon paste electrode is fabricated to determine lead ion concentration in its trace level in aqueous media with differential pulse voltammetry (DPV). The best performance is obtained by the carbon paste electrode composition including 20% of dithiodibezoic acid (DDA), 80% of high purity graphite powder and 60?µL of colloidal gold nanoparticle (AuNP) solution. The proposed electrode has a wide linear calibration response from 1?×?10^?9 to 6?×?10^?5 M with a detection limit of 6.6?×?10^?10?M, at pH 3.5. Seven replicate determination of 5?×?10^?8?M of lead ion concentration gives a relative standard deviation of 3.33%. The modified sensor is applied to determine lead contents in some environmental and biological Samples with satisfactory results.     

Simultaneous determination of lead and nickel in uranium by square-wave polarography

A sensitive method for the simultaneous determination of trace lead and nickel in uranium is described. These elements are separated from uranium by anion exchange and then determined by square-wave polarography using the alkaline cyanide solution as supporting electrolyte. The procedure is applicable to uranium metal and its compounds containing as little as 1 p.p.m. of lead and nickel.     

Study on the determination of trace rhenium (VII) by the adsorption differential pulse polarography

The determination of trace rhenium (VII) by differential pulse polarography in the system of H₂SO₄-(NH_sOH)₂ · H₂SO₄-TeO^2?₄ is markedly improved by the addition of Nitron, which is adsorbed on the surface of mercury electrode. The limit of detection is down to 2 × 10¹⁰ M. The adsorptive peak potential is ?0.80 V (vs. SCE). In the ranges of 5 × 10¹⁰—10^?8, 1 × 10^?5—10^?7 and 1 × 10^?7—10^?6M, there are good linear relationships between the peak current increment and the concentration, of which the relative standard deviations are 9.5, 6.6, 1.8% respectively with the correlation coefficients of linear regression of 0.995–0.999. The results relating to this polarographic wave show that it is an adsorption-catalytic wave. The mechanism of the electrode reaction is discussed.     

Simultaneous flow injection analysis of cadmium and lead with differential pulse voltammetric detection

A flow injection (FI) method using multiple differential pulse voltammetric detection for the simultaneous determination of two metal ions was developed and applied to the resolution of Cd(II)-Pb(II) mixtures. The metals are detected by applying two sequential pulses to a three-electrode voltammetric system that uses a flow-through cell accommodating a static mercury-drop working electrode. The influence of the electrode area, flow-rate, pulse frequency, pulse width and sampling time was investigated. Under the experimental conditions used, the two metals were found to interfere with each other. The use of a neural network allows the simultaneous determination of both, in mixtures, with good accuracy. The proposed method is applicable to other complex systems involving different working electrodes and more than two electroactive species.     

Trace determination of chromium in various water types by adsorption differential pulse voltammetry

Summary A new sensitive voltammetric method is presented for the determination of trace amounts of total chromium [Cr(III) and Cr(VI)] in natural waters. The method is based on the preconcentration of the Cr(III)-DTPA complex by adsorption at the HMDE at the potential of –1.0 V. The adsorbed complex is then reduced producing a response with a peak potential of –1.22 V and the peak height of the Cr(III) reduction is measured. The catalytic action of nitrate and bromate ions on the Cr(III)-DTPA reduction has been elucidated using cyclic voltammetry. The adsorption of chromium complexes at the HMDE was investigated using out-of-phase a. c. voltammetry and the potential range of adsorption was determined. Based on these investigations optimal conditions for the determination of the total chromium concentration in the range 20–2,000 ng/l have been established. The determination limit is 20 ng/l and the RSD is 5% for chromium concentrations 200 ng/l.The usefulness and wide scope of this new voltammetric method for reliable and highly sensitive chromium analysis down to the natural ultra trace levels existing in various types of natural waters is demonstrated by determinations of the total dissolved chromium content in river, lake, sea and rain water.

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Spurenbestimmung von Chrom in verschiedenen Wassertypen durch Adsorptions-Differentialpuls-Voltammetrie

Zusammenfassung Eine neue voltammetrische Methode zur Spurenbestimmung von Chrom [als Summe von Cr(III) und Cr(VI)] in natürlichen Gewässern wurde entwickelt. Die Methode beruht auf einer Anreicherung des Cr(III)-DTPA-Komplexes durch Adsorption an der hängenden Queck-silbertropfenelektrode beim Potential –1.0 V. Der adsorbierte Komplex wird anschließend im differentiellen Pulsmodus reduziert und die Peakhöhe beim Peakpotential –1.22 V gemessen. Die katalytische Wirkung von Nitrat- und Bromationen auf die Cr(III)-DTPA-Reduktion wurde mit der cyclischen Voltammetrie geklärt. Die Adsorption der Cr-Komplexe wurde zusätzlich mit der a.c.-Voltammetrie (kapazitive Komponente) untersucht und der Potentialbereich der Adsorption ermittelt. Aufgrund der Untersuchungen wurden die optimalen Bedingungen zur Chrombestimmung im Konzentrationsbereich 20–2000 ng/l festgelegt. Die Bestimmungsgrenze liegt bei 20 ng/l und die relative Standardabweichung beträgt 5% für Konzentrationen 200 ng/l. Die weite Anwendbarkeit der Methode für die zuverlässige und hochempfindliche Analyse von Chromspuren bis zu den natürlichen Ultraspurengehalten in verschiedenen Typen natürlicher Wässer wird an Beispielen der Analyse des gelösten Gesamtgehaltes von Chrom in Flußwasser, Seewasser, Meerwasser und Regenwasser aufgezeigt.

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Dedicated to Prof. Dr. H. Monien on the occasion of his 60th birthday

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Attached from Department of Chemistry of Warsaw University, Poland, within the scope of the joint research project on Eco-toxic Metals in the Environment     

Simultaneous determination of plutonium and americium in biological and environmental samples

A radiochemical method is given to determine the specific activity of²³⁸Pu, and²⁴¹Am from the global fallout in environmental and biological samples. The radiochemical recovery was for human livers Pu: 60–70%, Am: 40–60%; Bran: Pu: 50–70%, Am: 30–40%; Soil: Pu: 50–80%, Am: 30–50%. The resolution of the alpha-spectrum was for soils 30–40 keV and for livers and brans 40–60 KeV. To facilitate the wet ashing of large amounts of bran (15 kg), which are necessary to determine the presently very small activity concentrations of the transuranic elements in these types of samples, a fermentation process was employed. The procedure was tested by using NBS standard reference material and subsequently applied for the determination of Pu and Am from the global fallout in livers, plant tissues (bran), and soils.     

The determination of phenobarbital and diphenylhydantoin in blood by differential pulse polarography

A sensitive differential pulse polarographic assay was developed for the determination of phenobarbital or diphenylhydantoin in blood. The assay involves the selective extraction of the compound into chloroform from whole blood buffered to pH 7.0. After suitable “clean-up” of the sample, each compound is nitrated in 10% potassium nitrate in sulfuric acid at 25° for 1 h. The nitro-derivatives are extracted into ethyl acetate, and the residues are dissolved in 1 M phosphate buffer (pH 7.0) or 0.1 M sodium hydroxide for phenobarbital and diphenylhydantoin, respectively; the solutions are deoxygenated, and analyzed by differential pulse polarography. The overall recovery of phenobarbital and diphenylhydantoin from blood was 72.3% ±6.5 (s_r) and 76.7 ±2.3 (s_r) respectively. The sensitivity limit is 1–2 μg ml^-1 of blood for both compounds. A modified assay for the determination of both compounds in blood with t.l.c. separation was also developed.     

Determination of cadmium and lead in biological samples by Zeeman ETAAS using various chemical modifiers

The electrothermal atomic absorption spectrometric determination of cadmium and lead in biological certified reference materials (CRMs) has been carried out by using NH(4)H(2)PO(4), Ni, Pd, Ni+NH(4)H(2)PO(4), Pd+NH(4)H(2)PO(4) and Ni+Pd+NH(4)H(2)PO(4) as chemical modifiers. A comprehensive comparison was made among the modifiers in 1% Triton X-100 plus 0.2% nitric acid as diluent and without modifier. Zeeman background correction and graphite tubes inserted with platforms were used. Comparison was made in terms of pyrolysis and atomization temperatures, atomization and background absorption profiles. Ni+Pd+NH(4)H(2)PO(4) modifier mixture was found to be preferable for the determination of Cd and Pb. Pyrolysis temperatures of analytes were increased up to 900 degrees C for Cd and 1250 degrees C for Pb by using Ni+Pd+NH(4)H(2)PO(4) in 1% Triton X-100 plus 0.2% nitric acid diluent solution. Biological CRMs were analyzed to verify the accuracy and precision of this method. Depending on the biological sample type, the percent recoveries were increased from 62 to 102% for Cd and from 58 to 106% for Pb by using the proposed modifier mixture. The detection limits of Cd and Pb were found to be 0.04, 0.92 mug l(-1), respectively.     

The determination of cadmium,lead and copper in urine by differential pulse anodic stripping voltammetry

Differential pulse anodic stripping voltammetry is used for the simultaneous determination of cadmium, lead and copper in different types of urine samples. Unlike most biological samples, urine can be analyzed directly for cadmium and lead without pretreatment of the sample; a significant increase in sensitivity is obtained if the analysis is carried out at an elevated temperature. The complete decomposition of urine with a mixture of nitric, perchloric and sulphuric acids is also described; this procedure makes it possible to determine copper simultaneously. Good agreement was obtained between the two procedures, and the recovery of metals from spiked samples was satisfactory for both methods. The relative merits of the two approaches are discussed.