Cathodic adsorptive stripping voltammetric determination of uranium (VI) complexed with 2, 6-pyridinedicarboxylic acid

Uranium (VI) (U(VI)) forms a complex with dipicolinic acid (2, 6-pyridinedicarboxylic acid).This complex can be used for a highly sensitive and selective determination of uranium by adsorptive cathodic stripping voltammetry (ACSV) using a hanging mercury drop electrode (HMDE) as working electrode. Influence of effective parameters such as pH, concentration of ligand, accumulation potential and accumulation time on the sensitivity and selectivity were studied. The detection limit (3σ of the blank value) obtained under the optimal experimental conditions is 0.27 × 10⁻⁹ M after 150 s of the accumulation time. The peak current is proportional to the concentration of U(VI) in the range of 1 × 10⁻⁹ to 1.2 × 10⁻⁷ M. The relative standard deviation of 2.5% at the 3.5 × 10⁻⁸ M level was obtained. The interference of some metal ions and anions were studied. The application of this method was tested in the determination of uranium in synthetic and natural water samples.     

Experimental designs in the development of a new method for the sensitive determination of cadmium in seawater by adsorptive cathodic stripping voltammetry

A new differential pulse adsorptive cathodic stripping voltammetric (DPAdCSV) method for the direct determination of cadmium at subnanomolar levels in saline waters based on metal complexation with 2-acetylpyridine salicyloylhydrazone (APSH) and subsequent adsorptive deposition onto a hanging mercury drop electrode (HMDE) is presented. A study strategy based on experimental designs has been followed. Operating conditions were improved with exploratory (Plackett-Burman) and surface response (central composite) experimental designs, involving several chemical and instrumental parameters (pH, ligand concentration, pulse amplitude, time interval for voltage step, voltage step, deposition potential and deposition time). Analytical parameters as repeatability, linearity and accuracy were also investigated and a detection limit (DL) of 0.06 nM was achieved which could be lowered by extending the adsorption time. The interference of other metals and major salts present in seawater was also studied. The method was validated with reference water samples: NIST-SRM 1643d and BCR-CRM 505, showing good concordance with the certified values.     

Simultaneous determination of trace uranium(VI) and zinc(II) by adsorptive cathodic stripping voltammetry with aluminon ligand

Uranium(VI) complexed with aluminon (3-[bis(3-carboxy-4-hydroxy-phenyl)methylene]-6-oxo-1,4-cyclohexadiene-1-carboxylic acid triammonium salt) was determined by adsorptive cathodic stripping voltammetry (ACSV) using a hanging mercury drop electrode. Trace uranium(VI) and zinc(II) can be simultaneously determined in a single scan in the presence of aluminon and urea. Optimal conditions were found to be: accumulation time; 180–200 s, accumulation potential; 50 mV versus Ag/AgCl, scan rate; 40 mV s⁻¹, supporting electrolyte; 0.1 M sodium acetate buffer at pH 6.5–7.0, and concentration of aluminon; 1×10⁻⁶ M. The linear range of uranium(VI) and zinc(II) were observed over the concentration range 2–33 and 30–120 ng ml⁻¹, respectively. The detection limit (S/N=3) are 0.2 ng ml⁻¹ (uranium) and 30 ng ml⁻¹ (zinc). A good reproducibility shows RSDs of 2.5–4.0% (n=10). The procedure offers high selectivity, with the presence of urea masking some metal ions.     

An efficient approach to designing and optimizing the analysis of Ni(II) by AdCSV in seawater

A highly sensitive voltammetric method was developed for the determination of nickel in seawater at nanomolar concentrations. The measurement is based on the differential pulse cathodic adsorptive stripping of Ni(II) complexed with pyridoxal salicyloylhydrazone at a hanging mercury drop electrode. Optimal conditions were found following a two-step study strategy based on a Plackett Burman design and subsequently a modified simplex method. They were: deposition potential −0.8 V; deposition time 120 s; differential pulse scan mode; pulse amplitude −0.07 V; pulse time 0.04 s; voltage step 0.017 V; time interval for voltage step 0.05 s; supporting electrolyte ammonium chloride/ammonia (0.08 M, pH = 8.9) and concentration of PSH 5.32 × 10⁻⁶ M. The response of the system was found to be linear in a range of Ni concentrations from 0 to 306.7 × 10⁻⁹ M. The detection limit was found to be 0.04 × 10⁻⁹ M of Ni(II). The precision of the method was 1.4% for 3.4 × 10⁻⁸ M of Ni(II) and 1.48% for the blank at a significance level of 95% (n = 9). The method was free from interferences of inorganic salts and trace metals at usual concentrations in seawater. The application to seawater was demonstrated by analysis of CRM 505 and LGC 6016 certified reference estuarine water and real seawater samples from Tangier Bay (Morocco).     

Determination of uranium in seawater by flow-injection preconcentration on dodecylamidoxime-impregnated resin and spectrophotometric detection

A flow injection method has been developed for the determination of uranium in seawater combining the on-line preconcentration with spectrophotometric detection. An aliquot (10 mL) of the seawater sample adjusted to pH 5.5 was injected into the analytical system and uranium was adsorbed on the column packed with styrene-divinylbenzene copolymer resin (Bio-Beads SM-2) modified with dodecylamidoxime which showed high selectivity to uranium. Uranium was then eluted with 0.01 M hydrochloric acid and detected spectrophotometrically after the reaction with Chlorophosphonazo III. Interference from calcium and strontium was masked with cyclohexanediaminetetraacetic acid added to the chromogenic reagent solution. The sample throughput, the detection limit (3σ), and the preconcentration factor were 23 per hour, 0.13 μg/L, and 20, respectively, when the sample injection volume was kept at 10 mL. The precision at the 2 μg/L level was less than 4% (RSD). The proposed method was applied to the determination of uranium in the seawater samples collected off the Boso peninsula, Japan and the uranium concentration was found to be ca. 3 μg/L, which is close to the literature data. The yield of the recovery test ranged from 95% to 99%.     

流动注射光度法直接测定海水中的微量苯胺

基于苯胺与亚硝酸盐的重氮化反应及反应产物与甲萘酚的显色,借助流动分析技术,实现了海水中苯胺含量的分析测定。体系以30.9g/L的NaCl做载液、人工海水配制标准样品,对各个影响因素进行了优化。苯胺浓度在0.01～1.0mg/L范围内与相对峰高呈线性关系,线性方程ΔH(mV)=200.53ρ+1.0728(n=8,ρ为苯胺浓度mg/L),相关系数R2=0.9982。方法的检出限(3σ)为0.005mg/L,相对标准偏差(RSD)为4.8%(n=11)。考察了共存离子、不同盐度样品对分析测定的影响。用于实际海水样品的分析,回收率为95.8%～106.6%。     

Determination of Ultra Trace Amounts of Uranium (VI) by Adsorptive Stripping Voltammetry Using L-3-(3, 4-dihydroxy phenyl) Alanine as a Selective Complexing Agent

Abstract

The spectrophotometric behavior of uranium (VI) with L-3-(3, 4-dihydroxy phenyl) alanine (LDOPA) reagent revealed that the uranium can form a ML₂ complex with LDOPA in solution. Thus a highly sensitive adsorptive stripping voltammetric protocol for measuring of trace uranium, in which the preconcentration was achieved by adsorption of the uranium-LDOPA complex at hanging mercury drop electrode (HMDE), is described. Optimal conditions were found to be a 0.02 M ammonium buffer (pH 9.5) containing 2.0 × 10^?5 M (LDOPA), an accumulation potential of ? 0.1 V (versus Ag/AgCl) and an accumulation time of 120 sec.

The peak current and concentration of uranium accorded with linear relationship in the range of 0.5–300 ng ml^?1. The relative standard deviation (at 10 ng ml^?1) is 3.6% and the detection limit is 0.27 ng ml^?1. The interference of some common ions was studied. Applicability to different real samples is illustrated. The attractive behavior of this reagent holds great promise for routine environmental and industrial monitoring of uranium.     

Analytical applications of a differential technique in laser-induced fluorimetry: accurate and precise determination of uranium in concentrates and for designing microchemielectronic devices for on-line determination in processing industries

A novel instrumental technique for the direct, fast, accurate, and precise determination of uranium in concentrates and other U-rich materials (as well as to mineralized rocks) is presented. The proposed technique is an absolute methodology, based on the comparison of the fluorescence of the accurately known standard with a sample of similar but unknown concentration in the low operational range of the instrument (on same sample-dilution basis), by the use of H₃PO₄-NH₄H₂PO₄ as a fluorescence-enhancing reagent. The relative standard deviation of the proposed technique was 0.5-0.9% (n=9) at 18.1, 36.2, 61.2, and 99.6% U₃O₈. The proposed technique is suitable for the determination of uranium in samples arising from exploration projects, ores from mining operations, mill process samples, uranium ore concentrates leading to fuel fabrication as well as samples from environmental monitoring containing up to 100% uranium. The results are in good agreement with those obtained by titrimetric, gravimetric, and TBP extraction-H₂O₂ spectrophotometric methods. The precision of the technique is within the acceptable ‘pure geochemistry’ type of analysis (R.S.D. ∼ 1.0%) and is comparable even those obtained with titrimetric and gravimetric assay. The proposed differential technique coupled with flow injection may open up new advancement in instrumentation leading to design and development of microchemielectronic devices for direct on-line determination, more compatible with the tools of computer age as also to help in handling of radioactive solutions in chemical laboratories in uranium processing industries.     

Direct determination of bromide ions in seawater by capillary zone electrophoresis using polyethyleneimine-coated capillaries

A rapid and simple capillary electrophoretic method was developed for the direct determination of bromide ion in seawater. We have found an effective method, based on the use of polyethyleneimine-coated capillaries and the addition of sodium chloride to the background electrolyte. The use of coated capillaries with a cationic polymer changes the direction of the electroosmotic flow in the capillary, which favors the migration speed of the bromide ion and enables the use of low salt concentrations in the separation electrolyte. Bromide ion in seawater can be determined within 2 min using this system and 20 mmol L^-1 NaCl-containing separation electrolyte. The detection limit for the bromide ion was 0.45 g ml^-1. The method was applied to the determination of bromide ion in seawater samples collected from the Bosphorus and the Black Sea. Bromide contents in samples from 0 to 72 m depths varied between 33.2 and 72.8 mg L^-1 with a mean 3.0% RSD.     

Direct Simultaneous Determination of Cu,Ni and V in Seawater Using Adsorptive Cathodic Stripping Voltammetry with Mixed Ligands

An analytical procedure is proposed for the direct simultaneous determination in a single scan of Cu, Ni and V in seawater by means of adsorptive cathodic stripping voltammetry (ACSV) with mixed ligands (DMG and catechol). Optimum conditions for the determination of these three elements were studied. Detection limits of the technique depended upon the reproducibility of the procedura blank, and were found to be 0.5 nM for Cu, 0.4 nM for Ni and 0.3 nM for V. The method is suitable for the analysis of estuarine, coastal and open‐ocean waters, and especially to study the metal contamination in areas subject to oil spill events.     

连续流动分析法(CFA)快速测量废水中微量铀

应用FS-Ⅳ流动分析仪,以TBP-二甲苯作萃取剂,偶氮胂Ⅲ为反萃剂,NaNO3为盐析剂,EDTA为掩蔽剂,建立了废水中微量铀连续流动分析法.该方法的检出限(MDL)15.7 μg/L,加标回收率97%～104.5%.方法已应用于实际废水样的分析.     

How to Determine Uranium Faster and Cheaper by Adsorptive Stripping Voltammetry in Water Samples Containing Surface Active Compounds

A modification of the voltammetric procedure for the determination of uranium in the presence of cupferron using hanging mercury drop electrode is presented. The pulsed potential accumulation was proposed for the minimization of interferences of surface active substances. The calibration plot for U(VI) in the presence of 2 ppm Tritonu X‐100 was linear from 1.7×10^?10 to 2.0×10^?8 mol L^?1 for an accumulation time of 60 s, with correlation coefficient of 0.996. The application of this method was tested in the determination of uranium in certified reference material NASS‐5 and river water samples.     

Spectrophotometric determination of uranium in natural waters

A method for the spectrophotometric determination of uranium in samples of natural water is described. Ion exchange with Amberlite IR-120 (H⁺) to concentrate the metal was used. The absorption properties of the complex formed between uranium and the chromogenic reagent Arsenazo III, its stability over several hours, the effect of the pH on the ability of the resin to retain uranium, the reproducibility of the method and the effects of ionic interferences were considered. The sensitivity was 0.67 and 0.05 μg l^?1 of uranium for the direct and the addition methods, respectively. Uranium concentrations for the samples analysed were between 0.10 and 0.50 μg l^?1.     

Determination of uranium at ultratrace levels by time-resolved laser fluorimetry

Uranium at ultratrace levels in the pelleted cake from a NaF/Na₂CO₃/K₂CO₃ (10:45:45) fusion is determined by laser fluorimetry. Light scattering and fluorescence from impurities are greatly reduced by time-resolved fluorimetry. The optimum excitation wavelength is shown to be 360 nm from the signal-to-background ratio spectrum; emission is measured at 555 nm. The detection limit is 9 ng kg^?1 for a standard uranium sample. Relative standard deviations in the determination of ca. 50 ng kg^?1 uranium in silica samples are about 10%.     

Indirect determination of cyanide ion and hydrogen cyanide by adsorptive stripping voltammetry at a mercury electrode

An indirect voltammetric method is described for determination of cyanide ions and hydrogen cyanide, using the effect of cyanide on cathodic adsorptive stripping peak height of Cu-adenine. The method is based on competitive Cu complex formation reaction between adenine at the electrode surface and CN⁻ ions in solution. Under the optimum experimental conditions (pH=6.42 Britton-Robinson buffer, 1×10⁻⁴ M copper and 8×10⁻⁷ M adenine), the linear decrease of the peak current of Cu-adenine was observed, when the cyanide concentration was increased from 5×10⁻⁸ to 8×10⁻⁷ M. The detection limit was obtained as 1×10⁻⁸ M for 60 s accumulation time. The relative standard deviations for six measurements were 4 and 2% for the cyanide concentrations of 5×10⁻⁸ and 2×10⁻⁷ M, respectively. The method was applied to the determination of cyanide in various industrial waste waters such as electroplating waste water and also for determination of hydrogen cyanide in air samples.     

Simultaneous determination of uranium carbide dissolution products by capillary zone electrophoresis

Separation and simultaneous determination of a number of organic acid anions (oxalate, mellitate, trimellitate and benzoate) and U(VI) with direct UV detection is developed for analysis of uranium carbide (UC) dissolution products by capillary zone electrophoresis (CZE). Reverse polarity mode is used. It is found that complex formation of U(VI) with carbonate, used as a carrier electrolyte, allows U(VI) to be determined, as negatively charged species, in a single run with organic acid anions. Some parameters such as pH value, composition of electrolyte and detection wavelength are optimized. Under the chosen conditions (carbonate buffer (ionic strength of 100 mM), pH 9.8, 0.15 mM tetradecyltrimethylammonium bromide (TTAB)) a complete separation is achieved. Calibration plots are linear in two ranges of concentration for U(VI) (∼1 × 10⁻⁵ to 1 × 10⁻³), mellitate and trimellitate (∼5 × 10⁻⁶ to 5 × 10⁻⁴), and about one range (∼1 × 10⁻⁴ to 5 × 10⁻³) for oxalate and benzoate. Accuracy of the procedure is checked by the “added-found” method in standard mixture solutions. Relative standard deviation is within the range of 2–10% and the recovery is in the range of 90–110%. This method is applied for the analysis of real UC dissolution samples.     

浓缩—阳极溶出交换底液法测定饮用水中铅

通过浓缩－阳极溶出交换底液的方法测定饮用水的中铅含量，方法改善了伏安图形基线，降低了其了杂质影响，使测定结果更准确。     

Indirect determination of hexavalent chromium ion in complex matrices by adsorptive stripping voltammetry at a mercury electrode

A sensitive method for the determination of chromium ion(VI) in complex matrices such as crude oil and sludge is presented based on the decreasing effect of Cr(VI) on cathodic adsorptive stripping peak height of Cu-adenine complex. Under the optimum experimental conditions (pH 7.5 Britton-Robinson buffer, 5 × 10⁻⁵ M copper, 8 × 10⁻⁶ M adenine and accumulation potential −250 mV versus Ag/AgCl), a linear decrease of the peak current of Cu-adenine was observed, when the chromium(VI) concentration was increased from 5 μg L⁻¹ to 120 μg L⁻¹. Detection limit of 2 μg L⁻¹ was achieved for 120 s accumulation time. The relative standard deviations (R.S.D., %) were 1.8% and 4% for chromium(VI) concentrations of 18 μg L⁻¹ and 100 μg L⁻¹, respectively. The method was applied to the determination of chromium(VI) in the presence of high levels of chromium(III), in various real samples such as crude oil, crude oil tank button sludge, waste water and tap water samples. Effects of foreign ions and surfactants on the voltammetric peak and the influences of instrumental and analytical parameters were investigated in detail. The accuracy of the results was checked by ICP and/or AA.     

Stripping voltammetry for the determination of trace metal speciation and in-situ measurements of trace metal distributions in marine waters

Progress in marine chemistry has been driven by improved sampling and sample handling techniques, and developments in analytical chemistry. Consequently, during the last 20 years our understanding of marine trace metal biogeochemistry has improved a great deal. Stripping voltammetric techniques (anodic stripping voltammetry and adsorptive cathodic stripping voltammetry) have made an important contribution to this understanding. The selectivity and extremely low detection limits have made stripping voltammetry a widely used technique for trace metal speciation and trace metal distribution measurements in seawater. Stripping voltammetry is very suitable for ship-board and in-situ applications because of the portability, low cost and capability for automation of the voltammetric instrumentation. Future developments in stripping voltammetry can be expected in the field of stand-alone submersible voltammetric analysers, capable of continuous trace metal measurements. Future applications of stripping voltammetry can be found in the interactions between trace metal speciation and growth and the functioning of organisms in pristine and metal polluted marine waters.     

Estimation of uranium in bioassay samples of occupational workers by laser fluorimetry

A newly established uranium processing facility has been commissioned at BARC, Trombay. Monitoring of occupational workers is essential to assess intake of uranium in this facility. A group of 21 workers was selected for bioassay monitoring to assess the existing urinary excretion levels of uranium before the commencement of actual work. Bioassay samples collected from these workers were analyzed by ion-exchange technique followed by laser fluorimetry. Standard addition method was followed for estimation of uranium concentration in the samples. The minimum detectable activity by this technique is about 0.2 ng. The range of uranium observed in these samples varies from 19 to 132 ng/L. Few of these samples were also analyzed by fission track analysis technique and the results were found to be comparable to those obtained by laser fluorimetry. The urinary excretion rate observed for the individual can be regarded as a ‘personal baseline’ and will be treated as the existing level of uranium in urine for these workers at the facility.