Effect of organic colloids on ASV signals of Cd, Pb and Cu

The effect of organic colloids, such as humic and fulvic acids, on the ASV signals of Cd, Pb and Cu in acetate-buffer media has been investigated. Owing to their ability to adsorb metal ions, or form complexes (some sparingly soluble), the presence of the organic acids caused the magnitude of the signal peaks to decrease, the effect increasing with increase in organic acid: metal-ion ratio, and pH (from 5 to 8). Analysis before and after nitration through a 0.45-mum membrane indicated that most of the Cd retained was labile; in the Pb and Cu system less than half of the sorbed metal ion was labile, though a further fraction was displaced in the presence of Chelex 100 resin. The magnitude of the interference effect varied with the molarity of the medium and the presence of diverse anions (e.g. chloride, bromide) in the system. Cu displayed the most anomalous behaviour, with the stripping peak tending to broaden and split, particularly in the presence of humic acids. This behaviour was enhanced when the contact time with the preformed Hg film before the deposition/stripping cycle was increased above 5-10 min. This effect has been attributed to reduction (and subsequent oxidation) of Cu-humate species adsorbed on the mercury film.     

络合剂和添加剂对化学镀铜影响的电化学研究

以CuSO4·5H2O作主盐,乙二胺四乙酸二钠盐(Na2EDTA)作主络合剂,三乙醇胺(TEA)作辅助络合剂,2,2′＿联吡啶(dipyridine)作添加剂,组成化学镀铜液体系,研究络合剂、添加剂对该镀液电化学极化性能的影响,并结合化学沉积速率考察TEA和2,2′＿联吡啶对镀液性能的影响.     

Simultaneous determination of copper and lead in seawater using optimised thin-mercury film electrodes in situ plated in thiocyanate media

In the present work the anodic stripping voltammetric (ASV) methodology using a thin mercury film electrode in situ plated in thiocyanate media was re-assessed in order to allow the simultaneous determination of copper and lead in seawater. Under previously suggested conditions [6], i.e. using a concentration of thiocyanate of 5 mM, the ASV peaks of copper and lead overlapped due to the formation of a stable copper(I)-thiocyanate species, limiting the analytical determinations. Therefore, the best value for the thiocyanate concentration was re-evaluated: for 0.05 mM a trade-off between good resolution of the copper and lead peaks and high reproducibility of the mercury film formation/removing processes was achieved. In this media, the ASV peaks for Pb and Cu occurred, separated by 140 mV. Also, the in situ thin mercury film electrode was produced and removed with good repeatability, which was confirmed by the relative standard deviation values for the ASV determinations: 0.5% for Pb and 2.0% for Cu (10 replicate determinations in a solution with metal concentrations 1.5×10⁻⁸ M for lead and 2.2×10⁻⁸ M for copper). The optimised methodology was successfully applied to the determination of copper in the presence of lead, in certified seawater (NASS-5).     

Determination of copper in the presence of a large excess of bismuth by differential-pulse anodic-stripping voltammetry without preliminary separation

Conditions have been found which make possible the determination of copper in the presence of a large excess of bismuth by differential-pulse and anodic-stripping voltammetry without preliminary separation. The electrochemical activity of the bismuth, which usually interferes in the determination of copper, is inhibited by using tetrabutylammonium chloride (TBAC) as surfactant. In 0.2M EDTA and 0.01M ascorbic acid at pH 4.5 as supporting electrolyte without the surfactant present, trace levels of copper (1.5 x 10(-8)M) can be determined accurately if the molar ratio of bismuth to copper is not higher than 3, but if the electrolyte also contains TBAC at 0.01M concentration, bismuth can be tolerated in concentrations up to 10(-4)M, and the height of the copper peak is unaffected.     

Electrochemical study of the interaction between dsDNA and copper(I) using carbon paste and hanging mercury drop electrode

The interaction of copper(I) with double-stranded (ds) calf thymus DNA was studied in solution and at the electrode surface by means of transfer voltammetry using a carbon paste electrode (CPE) as working electrode in 0.2 M acetate buffer solution (pH 5.0). As a result of the interaction of Cu(I) between the base pairs of the dsDNA, the characteristic peaks of dsDNA, due to the oxidation of guanine and adenine, increased and after a certain concentration of Cu(I) a new peak at +1.37 V appeared, probably due to the formation of a purine-Cu(I) complex (dsDNA-Cu(I) complex). Accordingly, the interaction of copper(I) with calf thymus dsDNA was studied in solution as well as at the electrode surface using hanging mercury drop electrode (HMDE) by means of alternating current voltammetry (AC voltammetry) in 0.3 M NaCl and 50 mM sodium phosphate buffer (pH 8.5) as supporting electrolyte. Its interaction with DNA is shown to be time dependent. Significant changes in the characteristic peaks of dsDNA were observed after addition of higher concentration of Cu(I) to a solution containing dsDNA, as a result of the interaction between Cu(I) and dsDNA. All the experimental results indicate that Cu(I) can bind to DNA by electrostatic binding and form an association complex.     

Effects of competitive binding on the amperometric determination of copper with electrodes modified with chromotrope 2B

Electrodes modified with Chromotrope 2B incorporated by ion-exchange into a polycationic film of electropolymerized [Ru(v-bpy)(3)](2+) (v-bpy = 4-vinyl-4'-methyl-2,2'-bipyridyl) have been employed in the amperometric determination of copper in solution and exhibit very high sensitivity as well as linear calibration curves in the concentration range 7 x 10(-8)-1 x 10(-4)M. The effects of competing ligands, including chloride, bromide, oxalate, ammonia, acetate, citrate, borate, humic and fulvic acids, or the presence of competing metal ions such as cobalt or nickel on the uptake of copper by the modified electrodes have also been studied. The presence of competing ligands or metal ions decreases the analytical signal due to copper incorporation. The magnitude of this effect is dependent on the relative strength of coordination of the competing ligands for copper ions or of Chromotrope 2B for the competing metals, and also on the concentration of the interferents. The relevance of this work to speciation studies is discussed.     

The effect of inorganic particulates on the ASV signals of Cd, Pb and Cu

The potential influence of inorganic particulates on the ASV response of < 100-microg/l. levels of Cd, Pb and Cu, at a thin film mercury electrode, was examined by adding various weights of the solids to the acetate background electrolyte solution. Materials added included the hydrous oxides of Mn(IV), FE(III) or Al(III), clay minerals (kaolinite, illite, montmorillonite) and some contaminated sediments. Abrasion of the mercury film was minimized by deaerating the turbid solutions before their transfer to the measuring cell. The hydrous oxides specifically sorbed all three metal ions, resulting in peak-size changes that varied in magnitude with pH. With the clays, only sorption of Pb by illite or montmorillonite was detected. The presence of the solids had little effect on the peak position or half-peak breadth of the Cd or Pb signals, but the Cu peak parameters changed, indicating some hydroxy-species formation at higher pH. Some contaminated sediment samples released a significant fraction of their total metal content into acetate buffer solutions. Shielding the mercury film with a semipermeable membrane had a similar effect to filtering the suspension before analysis, but diffusion equilibrium was only slowly achieved (> 12 hr).     

Copper Sensing in Alkaline Electrolyte Using Anodic Stripping Voltammetry by Means of a Lead Mediator

Anodic stripping voltammetry (ASV) is an analysis technique that permits the selective and quantitative analysis of metal ion species in solution. It is most commonly applied in neutral to acidic electrolyte largely due to inherent metal ion solubility. Bismuth (Bi) is a common film used for ASV due to its good sensitivity, overall stability and insensitivity to O₂. ASV, utilizing a Bi film, along with cadmium (Cd) and lead (Pb) as the plating mediators, has recently been adapted to determine zinc (Zn) concentrations in highly alkaline environments (30 % NaOH or 35 % M KOH). Successful analysis of Zn in alkaline relies on the ability of the hydroxide to form soluble metal anion species, such as Bi(OH)₄⁻ and Zn(OH)₄²⁻. Here, we look to extend this technique to detect and quantify copper (Cu) ions in these highly basic electrolytes. However, in general, the use of ASV to detect and quantify Cu ion concentrations is notoriously difficult as the Cu stripping peak potential overlays with that of Bi from the common Bi film electrode. Here, an ASV method for determining Cu concentration in alkaline solutions is developed utilizing Pb as a deposition mediator. As such, it was found that when analyzing Cu solutions in the presence of Pb, the stripping voltammetry curves present separate and defined Cu stripping peaks. Different analyzes were made to find the best stripping voltammetry performance conditions. As such, an accumulation time of 5 minutes, an accumulation potential of≤−1.45 V vs. Hg/HgO, and a concentration of 35 wt% KOH were determined to be the conditions that presented the best ASV results. Utilizing these conditions, calibration curves in the presence of 5.0 ppm Pb showed the best linear stripping signal correlation with an r‐squared value of 0.991 and a limit of detection (LOD) of 0.67 ppm. These results give way to evaluating Cu concentrations using ASV in aqueous alkaline solutions.     

Sequential potentiometric complexometric redox determination of iron(III) and cobalt(II) with application to alloys

A simple potentiometric method is presented for successive determination of iron(III) and cobalt(II) by complexometric titration of the iron(III) with EDTA at pH 2 and 40 degrees , followed by redox titration of the cobalt(II) complex with 1,10-phenanthroline or 2,2'-bipyridyl at pH 4-5 and 40 degrees , with gold(III). There is no interference in either determination from common metal ions other than copper(II), which severely affects the cobalt determination but can be removed by electrolysis. The method has been successfully applied to determination of iron and cobalt in Kovar and Alnico magnet alloys.     

Synthesis, physico-chemical and DNA interaction studies of homo- and hetero-trinuclear complexes

Synthesis and characterization of three new trinuclear metal complexes of type Cu3, Cu2Zn and Cu2Ni have been achieved by assembling simple mononuclear complexes, namely 2,2'-bipyridyl 3,4-dihydroxo benzaldehyde copper(II) complex and diethylenetriamine complexes of copper(II), nickel(II) and zinc(II) ions, through the reaction of coordinated ligands. The FAB mass spectra for the complexes show fragmentation pattern in accordance with the molecular formula. The frozen electron paramagnetic resonance (EPR) spectrum of tricopper complex shows two sets of parallel lines with approximately 2:1 ratio. The simulation has been carried out by considering dipolar interaction between the two types of copper ions present in the complex. The trimetallic complexes, Cu3, Cu2Ni and Cu2Zn show strong intercalation type of interaction with Calf thymus DNA in 0.02 mol L(-1) of phosphate buffer containing 60 mmol sodium chloride at pH 7.0 at room temperature. The binding constant is found to be in the order Cu3相似文献   

Enantioselective Friedel-Crafts alkylation reactions catalyzed by a chiral nonracemic C2-symmetric 2,2'-bipyridyl copper(II) complex

Enantioselective Friedel-Crafts alkylation reactions of a series of substituted indoles with methyl trifluoropyruvate, catalyzed by a chiral nonracemic C(2)-symmetric 2,2'-bipyridyl copper(II) triflate complex, are described. The corresponding 3,3,3-trifluoro-2-hydroxy-2-indole-3-yl-propionic acid methyl esters were formed in good yield and in high enantiomeric excess (up to 90%). This is the first report of the use of a chiral nonracemic 2,2'-bipyridyl ligand in catalytic and enantioselective Friedel-Crafts alkylation reactions. The structural characterization of a copper(II) chloride complex of the chiral 2,2'-bipyridyl ligand by X-ray crystallography is also presented. [reaction: see text]     

胆红素、铜离子与2,2′-联吡啶作用的光谱研究

基于2,2′-联吡啶芳杂环羟基化法,采用荧光光谱研究了胆红素与Cu2 的相互作用。探讨了胆红素与Cu2 反应生成羟自由基(.OH),2,2′-联吡啶发生芳杂环羟基化反应的过程和反应机理,产生的羟自由基导致无荧光的2,2′-联吡啶发生芳杂环羟基化,生成强荧光物质;加入自由基猝灭剂后,荧光强度的增强明显减弱。考察了试剂加入顺序、反应时间、酸度、Cu2 浓度、胆红素浓度,以及2,2′-联吡啶浓度等的影响。     

Copper speciation by competing ligand exchange method using differential pulse anodic stripping voltammetry with ethylenediaminetetraacetic acid (EDTA) as competing ligand

A technique has been developed to study chemical speciation of copper in freshwaters by competing ligand exchange (CLE) method using anodic stripping voltammetry (ASV) in the differential pulse (DP) mode with ethylenediaminetetraacetic acid (EDTA) as a competing ligand. The voltammetric behavior of Cu(II)-EDTA complex has been investigated using DPASV. When DPASV is used at an appropriate deposition potential, the inert Cu(II)-EDTA complex becomes electroactive, and is reduced directly. Furthermore, at the same deposition potential, Cu(II)-fuvic acid and Cu(II)-humic acid complexes do not contribute significantly to the analytical signal, which makes EDTA a suitable competing ligand in the determination of copper speciation using CLE-ASV. This method has been applied to freshwater samples from Rideau Canal (Ottawa, ON, Canada). The analysis of the copper titration data of these freshwater samples has indicated the presence of a very strong copper-binding ligand with a conditional stability constant of approximately 10²⁰ and a corresponding very high concentration (above 100 nM) of the ligand.     

Synthesis and evaluation of new chiral nonracemic C2-symmetric and unsymmetric 2,2'-bipyridyl ligands

The synthesis of a series of chiral nonracemic and C2-symmetric 2,2'-bipyridyl ligands (R = Me, i-Pr and Ph) as well as the syntheses of the corresponding unsymmetric 2,2'-bipyridyl ligands (R = Me and Ph) is described. These bipyridyl ligands were prepared, in a notably direct and modular fashion, from the readily available and corresponding 2-chloropyridine acetals (R = Me, i-Pr and Ph). The bipyridyl ligands were evaluated in copper(I)-catalyzed cyclopropanation reactions of styrene with the ethyl and t-butyl esters of diazoacetic acid. The stereoselectivities, as well as the yields of the cyclopropanation reactions, were dependant on the ratio of the bipyridyl ligands and copper triflate that was employed. The best result was obtained in the asymmetric cyclopropanation reaction of styrene and tert-butyl diazoacetate with the C2-symmetric bipyridyl ligand (R = i-Pr). This afforded the corresponding trans-cyclopropane in good diastereoselectivity (4 : 1) and in moderate enantioselectivity (44% ee). The X-ray structure determination of a complex formed between the C2-symmetric 2,2'-bipyridyl ligand (R = Ph) and copper(I) chloride showed that two bipyridyl ligands had coordinated to the copper(I) ion. This information, along with the results of a series of cyclopropanation reactions and NMR data, led to the conclusion that the 2,2'-bipyridyl ligands had the propensity to form catalytically inactive bis-ligated copper(I) species in solution that were in equilibrium with catalytically active copper(i) triflate and the desired mono-ligated copper(I) species. Moreover, it was observed that the complex of the bipyridyl ligand (R = Ph) and copper(I) chloride had a particularly large optical rotation (sodium D-line). The maximum positive optical rotation was subsequently found to be +1.1 x 10(4) at 304 nm and the maximum negative optical rotation was -1.3 x 10(4) at 329 nm.     

The Study of Various Rhenium Compounds by Capillary Electrophoresis

The conditions for the synthesis of rhenium compounds (pH, reaction time, concentration of reducing agent) have been determined previously by thin-layer chromatography. A Britton-Robinson buffer solution has been selected as a carrier electrolyte due to its possible use in a wide interval of pH, mainly at optimal pH for the formation of the complexes studied. The same electrolyte has been previously applied also in case of the study of rhenium and technetium complexes by polarography. The electrophoretic experiments have been carried out under both standard and reverse polarities with direct UV detection at the wavelength 214 nm and 20 °C. The signal of perrhenate has been observed at the reverse polarity (outlet+, inlet–), of reduced rhenium [probably Re(IV)] under normal polarity. The formation of rhenium complexes with EDTA has been shown by lowering of the cationic rhenium signal due to the addition of the ligand. The rhenium complexes with EDTA are observable at reverse mode of CE. The formation of rhenium complexes with HEDP (hydroxyethylidenediphosphonic acid) has been studied in two different carrier electrolytes — 40 mM Britton-Robinson buffer solution and 50 mM phosphate buffer with 20 mM HEDP. The mechanism of perrhenate reduction by stannous chloride and of the formation of rhenium complexes with EDTA has been determined. The necessity of the presence of ascorbic acid as an antioxidant in the reaction mixture at different pH values has been described as well.     

Electrochemical masking of large amounts of copper in dpasv and the determination of thallium in the presence of a large excess of copper

The influence of the following surfactants on the peak of copper in 0.2M EDTA at pH 4.5 was investigated: polyoxyethylated alkylphenols having an average of 3 and 9.5 ethylene oxide units; polyoxyethylene alcohols having 4 and 7 ethylene oxide units; poly(ethylene glycols) having M.W. 4000, 9000 and 20000; hexadecyltributylphosphonium bromide (HDTBPB), tetraphenylphosphonium bromide (TPPB),N,N,N,N,N',N',N-examethylhexamethylenediammonium bromide (HMB), benzyl(di-isobutylphenoxyethoxy) dimethylammonium chloride (Hyamine 1622), hexadecyltrimethylammonium bromide (HDTMAB), hexadecyldimethylbenzylammonium chloride (HDDMBAC) and tetrabutylammonium chloride (TBAC). HDDMBAC, as well as all the substances examined which contained an ethylene oxide chain, completely suppressed the copper peak. HDTBPB and TPPB partially suppressed the peak, whereas HDTMAB, HMB and Hyamine 1622 enhanced it. TBAC was without effect. In 0.2M EDTA at pH 4.5 containing TBAC at 0.01M concentration and 10 ppm of Rokafenol N-3, Cu(II), Pb(II) and Bi(III) can be tolerated at concentrations of up to 0.05M, the height of the thallium peak being unaffected. The precision of the determination (3–10%) and the recovery are satisfactory. A 10³-fold ratio of Fe(III) to Tl(I) does not interfere with the determination.     

Determination of iron(II) with chemically-modified carbon-paste electrodes

The utility of carbon-paste electrodes modified with 2,2'-bipyridyl and Nafion for the differential pulse voltammetric determination of iron(II) in aqueous medium is demonstrated. The method is based on formation of the 2,2'-bipyridyl complex of iron(II) and its accumulation by the Nafion. The differential pulse voltammetric response of the accumulated complex is used as the analytical signal. The response was evaluated with respect to carbon-paste composition, preconcentration time, pH, iron(II) concentration and other variables. A 3-min accumulation period permits measurement of iron(II) down to 10(-8)M, and a relative standard deviation of 3.8% for 2 x 10(-6)M iron(II). Rapid and convenient chemical renewal allows use of a single modified carbon-paste electrode in multiple analytical measurements over several days. The proposed procedure was applied to the determination of iron in certified standard reference materials and trace iron in natural waters.     

Emissive Mononuclear Cu(I) Triphenylphosphine Complexes with Functionalized 6-tert-Butoxycarbonyl-2,2'-bipyridine

Two new emissive mononuclear copper(I) triphenylphosphine complexes with functionalized 6-tert- butoxycarbonyl-2,2'-bipyridine chelating ligands were prepared and characterized. Each Cu(I) cation has a markedly distorted P₂N₂ tetrahedral array with two different Cu—N bond distances, due to the addition of the bulky tert-butoxycarbonyl group at the 6-position of the 2,2'-bipyridyl ring. A weak low-energy broad absorption band appears at 330—500 nm in their CH₂Cl₂ solutions, which is influenced by the methylation of the 2,2'-bipyridyl ring. At room temperature, the photoluminescence can be clearly observed both in degassed CH₂Cl₂ solution and in the solid state, because of the introduction of the bulky tert-butoxycarbonyl substituent, and the emission properties are remarkably affected by both the methylation and the alkoxycarbonyl variation of the 2,2'-bipyridyl ring. It is shown that the introduction of the bulky tert-butoxycarbonyl group is favorable for improving the emission properties of the 6-alkoxycarbonyl-2,2'-bipyridine-based cuprous complexes.     

Spectrophotometric study of the beryllium-thorin complex and its application to the determination of beryllium in alloys

A spectrophotornetric study of the beryllium complex with purified thorin shows the formation of a I : I complex at pH 12. The dissociation constant obtained after successive corrections for reagent absorbance is 1.38·10^-7. Beryllium in concentrations of 0.05% to 2.0% in copper base, zinc base, aluminiuin base and ferrous alloys can be determined by the formation of the thorin complex after its preliminary separation as accetylacetonate in presence of EDTA.     

Analysis of rain water by differential-pulse stripping voltammetry in nitric acid medium

Differential-pulse anodic stripping voltammetry is applied to determine cadmium, lead and copper in rain water acidified with nitric acid to pH 1.5, and zinc after partial neutralization to pH 4.5. Subsequently, cobalt and nickel are measured in the adsorptive mode after formation of their dimethylglyoximates. The effects of pH on the stripping peaks for Zn, Cd, Pb and Cu and of chloride on the stripping peak of copper are reported. Good agreement is found with d.p.s.v. determinations in hydrochloric acid medium and with a.a.s. measurements in most cases. Excellent accuracy is demonstrated; the average relative standard deviation per measurement appears to be between 12 and 22% for the overall analytical procedure for concentrations of 0.15–50 μgl^?1 of the various metals in the samples.