Tubular Detector of Silver Solid Amalgam for Electrochemical Measurements in Flow Systems

This paper presents the application of the tubular detector based on silver solid amalgam (TD‐AgSA) for electrochemical determinations of reducible inorganic (Cd²⁺, Zn²⁺) and organic (4‐nitrophenol) compounds under flow injection analysis conditions. The newly developed TD‐AgSA is simple, robust and inexpensive. The limits of detections of Zn²⁺, Cd²⁺ and 4‐nitrophenol are 1.4×10^?6, 7.0×10^?7, and 5.0×10^?7 mol dm^?3, respectively (i.e. 0.09, 0.08 and 0.07 ppm). The obtained results proved the long‐term stability of the detector (RSD of the determination of Zn²⁺, Cd²⁺, and 4‐nitrophenol were 0.8, 0.9 and 0.8 % (n=10; c_Zn=7.7×10^?5 mol dm^?3, c_Cd=4.5×10^?5 mol dm^?3 and c_4‐NPh=3.6×10^?5 mol dm^?3), respectively and its applicability for cathodic measurements in aqueous solutions at potentials up to ?2 V.     

Selective and efficient liquid membrane transport of gold as gold cyanide using an anion carrier

The facilitated transport of Au(III) from cyanide solutions through a bulk liquid membrane is reported. The organic phase consisted of a chloroform solution containing Victoria blue dye as the Au(CN)⁻₄ carrier. The effects of pH of source phase, potassium cyanide concentration in source phase, Victoria blue concentration in the organic phase and sodium hydroxide in the receiving phase on the efficiency of transport process were examined. Under optimum conditions the extent of Au(CN)⁻₄ transport across the liquid membrane was about 97% after 180 min. The carrier can selectively and efficiently transport Au(CN)⁻₄ ion from the aqueous solutions containing other cations such as alkali and alkaline earth, Zn²⁺, Pb²⁺, Cu²⁺, Cd²⁺, Hg²⁺, Ag⁺, Co²⁺, Fe²⁺, Pt²⁺, Pd²⁺ and Ni²⁺.     

Interfering influence of silver on the voltammetric behaviour of Cd2+ and Zn2+ ions on hmde in supporting electrolytes containing nitrates

A new kind of secondarily formed peaks was found in cyclic and stripping voltammetry in neutral sulphate, perchlorate and nitrate supporting electrolytes containing some divalent cations and a substance (for example O₂), the reduction of which gives as a by-product OH^? ions. The hydroxides deposited in the vicinity of the mercury electrode, in the course of a cathodic scan, react during the anodic scan according to the reaction Hg+Me(OH)₂=Hg(OH)₂+Me²⁺+2e forming a new, separate anodic peak.It was found that silver exerts a catalytic effect on the reduction of NO₃^? ions on the mercury electrode. In neutral nitrate supporting electrolyte containing Ag⁺ ions the hydroxides of some cations (Cd²⁺, Zn²⁺, Mn²⁺, Co²⁺ and Ni²⁺) were deposited during the cathodic scan or during the preelectrolysis. Afterwards, in the course of the anodic scan, a new peak, of the kind described above, was observed. The same effect was formerly interpreted, for Zn²⁺ and Cd²⁺, as evidence for the formation of intermetallic compounds, AgZn and AgCd.     

Synthesis and Structures of the Novel Biferrocenamine‐Based Receptor and its Voltammetric Responses to Transition Metal Ions

Reactions of formylferrocene and 1,2‐di‐(o‐aminophenoxy)ethane yield the novel bis(ferrocenyl) receptor (FcL). This compound has been characterized by IR, ¹H NMR and elemental analysis. In addition, the electrochemical behavior of FcL was investigated in detail in 0.1 M tetra‐n‐butylammonium perchlorate (TBAP) + CH₃CN by cyclic voltammetry (CV) and chronoamperometry. Its co‐ordination properties with metal ions in acetonitrile were also studied. The FcL shows a two‐wave behavior for H⁺, Cu²⁺, Zn²⁺ and Ni²⁺, but was unresponsive to Mg²⁺ and Ca²⁺. The maximum oxidation peak shift of about 250 mV was found for FcL in the presence of Cu²⁺, Zn²⁺ or Ni²⁺.     

Study of Complex Formation between 5,7‐Diiodo‐8‐hydroxyquinoline and Zn2+, Cd2+, Pb2+ and Tl+ Cations in Binary Non‐Aqueous Solvents Using Square Wave Polarography Technique (SWP)

The complexation reaction between Zn²⁺, Pb²⁺, Cd²⁺ and Tl⁺ cations by 5,7‐diiodo‐8‐hydroxyquinoline (IQN) was studied in the Dimethylformamide /Acetonitril (DMF‐AN) binary system using square wave polarography technique. The stoichiometry and stability of the complexes were determined by monitoring the shifts in half‐wave or peak potential of the polarographic waves of metal ions against the ligand concentration. The stoichiometry of the complexes was found to be 1:1. The results obtained show that there is an inverse relationship between the formation constant of the complexes and the donor number of solvent base on the Guttmann donocity scale. In all cases the formation constants increased with increasing amounts of AN in these binary systems. The selectivity order for IQN complexes with the cations is Zn²⁺ > Pb²⁺ > Cd²⁺ > Tl⁺.     

Anodic Stripping Voltammetry of Heavy Metals on a Metal Catalyst Free Carbon Nanotube Electrode

Anodic stripping voltammetry (ASV) determination of Pb²⁺, Cd²⁺, and Zn²⁺ was done using metal catalyst free carbon nanotube (MCFCN) electrodes. Osteryoung square wave stripping voltammetry (OSWSV) was selected for detection. The MCFCNTs are synthesized via Carbo Thermal Carbide Conversion method which leads to residual transition metal free in the CNT structure. The new material shows very good results in detecting heavy metal ions, such as Pb²⁺, Cd²⁺, and Zn²⁺. The calculated limits of detection were 13 nM, 32 nM and 50 nM for Pb²⁺, Cd²⁺ and Zn²⁺, respectively with a deposition time of 150 s.     

A voltammetric sensor for simultaneous determination of lead,cadmium and zinc on an activated carbon fiber rod

A simple, low cost and sensitive voltammetric sensor was developed for the simultaneous detection of Pb²⁺, Cd²⁺, and Zn²⁺ based on a disposable carbon fiber rod (CFR). The important factors to enhance the sensing property were creation of a clean surface by dealing with CFR at a high potential and electrochemical deposition of Bi film to improve the accumulation of heavy metal ions.     

Bemerkungen zu den Reaktionen mit Quecksilberrhodanid-Ion

Zusammenfassung Die Krystallform und die Farbe der reinen Verbindungen Zn-, Cd-, Co- und Cu[Hg(CNS)₄] werden beschrieben.Es wird gezeigt, daß die Empfindlichkeit des Zn-, Cd-, Co- und Cu-Nachweises gesteigert werden kann, wenn man statt des Behrens-Reagens reines, festes (NH₄)₂[Hg(CNS)₄] gebraucht. Die Empfindlichkeit des Nachweises der Ionen ist in Tabelle 5 (S. 69) zu finden.Bei gleichzeitiger Fällung von Zn^.. und Co^.., Zn^.. und Cu^.., Cd^.. und Co^.. und Cd^.. und Cu^.. entstehen intensiv gefärbte Substitutionsmischkrystalle, deren Löslichkeit im Wasser geringer ist, als die der reinen Komponenten. Durch diese Eigenschaften der sich bildenden Mischkrystalle kann bekanntlich die Empfindlichkeit des Nachweises der Ionen Cu^.., Co^.., Zn^.. und Cd^.. noch weiter gesteigert werden.Eine Neubestimmung der Empfindlichkeiten wurde vorgenommen (Tabelle 6, S. 70).     

Molybdenum cluster chalcogenides Mo6X8: Electrochemical intercalation of closed shell ions Zn2+, Cd2+, and Na

The intercalation ofd¹⁰ ions Zn²⁺ and Cd²⁺ by electron/ion transfer reactions into the Chevrel-type molybdenum cluster chalcogenidesMo₆X₈ (X =S, Se) demonstrates the competitive influence of electronic and steric factors upon these processes. The following rhombohedral phases have been identified: Zn₁Mo₆S₈, Zn₂Mo₆S₈, Zn₁Mo₆Se₈, Zn₂Mo₆Se₈, Cd₁Mo₆S₈, Cd₁Mo₆Se₈, and Cd₂Mo₆Se₈. Thermodynamic data and chemical diffusion coefficients are given. The intercalation of Na⁺, which has an ionic radius close to that of Cd²⁺, exhibits a strong influence of kinetics leading to the partial irreversibility of the reaction and the formation Na₁Mo₆S₈ and Na₁Mo₆Se₈, the first cubic phases among the molybdenum cluster chalcogenidesA_xMo₆X₈.     

Metal Complexes with Macrocylclic Ligands. Part XXXV. Stabilities of some bivalent metal-ion complexes with 1,4,7-triazacyclononane-1-acetie acid

The stability constants of the Mn²⁺, Zn²⁺, Ni²⁺, pb²⁺, and Cd²⁺ complexes with 1,4,7-triazacylononane-1-acetic acid (noma) were determined at 25° and 0.5M (KNO₃) by potentiometric titrations. The species [ML] and [ML(OH)] were found in al cases except for Ni²⁺, whereas [ML₂] was only detected for Cd²⁺. For the complexes [ML], the order of stability is Mn²⁺ < Cd²⁺ < pb²⁺ < Zn²⁺ < Zn²⁺ < Ni²⁺ < Cu ²⁺, which is consisten with the Irvin-Williams Series.     

Syntheses,structures of N‐(substituted)‐2‐aza‐[3]‐ferrocenophanes and their application as redox sensor for Cu2+ ion

Rigid N‐(substituted)‐2‐aza‐[3]‐ferrocenophanes L1 and L2 were easily synthesized from 1,1 ‐dicarboxyaldehydeferrocene and the corresponding amines. Ligands L1 and L2 were characterized by ¹H NMR, ¹³C NMR and single‐crystal X‐ray crystallography. The coordination abilities of L1 and L2 with metal ions such as Cu²⁺, Mg²⁺, Ni²⁺, Zn²⁺, Pb²⁺ and Cd²⁺ were evaluated by cyclic voltammetry. The electrochemical shift (ΔE_1/2) of 125 mV was observed in the presence of Cu²⁺ ion, while no significant shift of the Fc/Fc + couple was observed when Mg²⁺, Ni²⁺, Zn²⁺, Pb²⁺, Cd²⁺ metal ions were added to the solution of L1 in the mixture of MeOH and H₂O. Moreover, the extent of the anodic shift of redox potentials was approximately equal to that induced by Cu²⁺ alone when a mixture of Cu²⁺, Mg²⁺, Ni²⁺, Zn²⁺, Pb²⁺ and Cd²⁺ was added to a solution of L1. Ligand L1 was proved to selectively sense Cu²⁺ in the presence of large, excessive first‐row transition and late‐transition metal cations. The coordination model was proposed from the results of controlled experiments and quantum calculations. Copyright © 2012 John Wiley & Sons, Ltd.     

On the different coordination of Ni, Zn and Cd cations in their model Schiff base complexes - Single crystal X-ray and solid state NMR studies

Three model metal complexes: Ni(NCS)L, Zn₂(NCS)₂L₂ and Cd₂(NCS)₂L₂, consisting of the SCN⁻ anion(s) and L = 2-[(2-dimethylaminoethylimino)-methyl]-phenolate, have been studied by X-ray diffraction and solid state NMR spectroscopy. The metal cations in these complexes have different coordination modes: Ni²⁺ is almost square-planar, the Zn²⁺ cation in Zn₂(NCS)₂L₂ is pentacoordinated, whereas Cd²⁺ is penta- and hexacoordinated in [Cd₂(NCS)₂L₂]. The different coordination of the metal cations influences the chemical shifts of the metal cations and also the nitrogen atoms. These chemical shifts can be correlated with the M-N and M-O bond lengths (M = Ni²⁺, Zn²⁺, Cd²⁺).     

Study of the thermal decomposition of MSO4 (M = Zn(II), Cd(II), Hg(II)) in a sodium nitrate—potassium nitrate melt

MSO₄ (M = Zn²⁺, Cd²⁺, Hg²⁺) dissolves in the molten NaNO₃—KNO₃ eutectic and is decomposed on further heating. The kinetics of decomposition have been studied at different temperatures. The decomposition of CdSO₄ and HgSO₄ in the eutectic melt obey first-order kinetics whereas the decomposition of ZnSO₄ at 420–460°C obeys second-order kinetics. However, at 480°C the decomposition of ZnSO₄ obeys first-order kinetics. The mechanism of decomposition has been given as M²⁺ +SO^2?₄ +Na⁺ +K⁺ +2NO^?₃ ? (Na,K)SO₄ + M²⁺ +2NO^?₃ M²⁺ +NO^?₃ → MO+NO⁺₂ NO^?₃ +NO⁺₂ → NO₂ + $\text{1}\text{2}$O₂ Some of the end products have been analysed by X-ray diffraction.     

Calculation of the equilibrium constants and binding cooperativity parameters of ammonia with Group II metal cations in solution

The matrix model was used to analyze the distribution diagrams and formation functions of ammonia complexes [M(NH₃) _n ]²⁺ (n = 0−4) of Group II metal ions (Mg²⁺, Ca²⁺, Zn²⁺, Cd²⁺, and Hg²⁺) in solution. Intrinsic binding constants of the ligand (K _in) and mutual influence corrections (ω) for complex formation with aqua ions in solution were calculated. The equilibrium constants were calculated by the matrix method. The coordination sphere of Mg²⁺, Ca²⁺, and Zn²⁺ by ammonia in a cooperative manner; with Cd²⁺ and Hg²⁺, both cooperative and anticooperative binding occur concurrently. Possibilities for differentiation between tetrahedral and square planar coordination polyhedra on the basis of the characteristic features of ligand binding, determined by the matrix model, are discussed.     

Potentiometric titration of trace amounts of mercury with dithiooxamide

Titration with dithiooxamide in potassium hydrogenphthalate medium (pH 5–6) is suitable for the determination of mercury in concentrations above 0.05 ppm. The precision in the range 0.05–1.0 ppm Hg is ? 4%. Significant amounts of sulphate, nitrate, Zn²⁺, Cd²⁺ and Pb²⁺ and small amounts of Ni²⁺, Co²⁺ and Al³⁺ can be tolerated, but Fe³⁺, Cu²⁺ and Ag⁺ interfere.     

Study of some metallic silicates as ion-exchangers

The extraction of ammine complexes of Cu²⁺, Cd²⁺, Ni²⁺, Co²⁺ and Zn²⁺ by synthesised manganese, nickel and zinc silicates has been studied at different pH and ionic concentrations in the external solution. It has been found that the uptake of the metal ion Co²⁺, Cu²⁺ and Zn²⁺ increases with increase in pH of the external solution, attains a maximum and then decreases. However, the uptake for Cd²⁺ and Ni²⁺ increases continuously. The q_A values of all the silicates increases with the increase in the concentration of the exchanging ion and its order for the investigated metal ions is Ni²⁺ < Co²⁺ < Cd²⁺ < Zn²⁺ < Cu²⁺.     

Study on the Liquid‐Solid Flotation Separation of Cadmium by Ammonium Sulfate‐Potassium Iodide‐Cetylpyridine Chloride‐Water System

The liquid‐solid flotation separation behaviors of Cd²⁺ in ammonium sulfate‐potassium iodide‐cetylpyridine chloride‐water system and the conditions for the separation of Cd²⁺ from other metal ions were studied. The results showed that in the presence of 1.0 g (NH₄)₂SO₄ and when the dosage of 0.1 M potassium iodide was 2.0 mL and 0.01 M cetylpyridine chloride (CPC) solution was 1.0 mL respectively, the formed water‐insoluble ternary association complex of KI‐CPC‐Cd floated above water phase and liquid‐solid phases were formed with clear interface. In this condition, Zn²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺ and Al³⁺ could not be floated and Cd²⁺ was floated quantitatively at pH 5.0. Therefore, the quantitative separation of Cd²⁺ from the above metal ions could be achieved. The quantitative flotation separation determination of Cd²⁺ in the sample of synthetic water and industrial waster water was performed, and the results agreed well with those by AAS method. The recoveries were 97.2%～102.4%, and the RSD was 1.8%.     

Kinetics of Iodous Acid Disproportionation

The iodous acid disproportionation is autocatalytic, and it is not easy to measure the rate constant of the step 2IO₂H → IO₃^? + IOH + H⁺ separately. Hg(II) was used previously to suppress the autocatalytic pathway, but this method presents difficulties discussed in this work. A more effective method is the use of crotonic acid, an effective IOH scavenger. It suppresses side reactions, and a purely second‐order rate law is obtained. The rate constant decreases from 5 to 0.2 M^?1 s^?1 when the sulfuric acid concentration increases from 0.08 to 0.60 M. The observed decrease could be explained if IO₂^? reacts faster than IO₂H. This may have consequences for the mechanism of the oscillating Bray–Liebhafsky reaction.     

Simultaneous,Selective and Highly Sensitive Voltammetric Determination of Lead,Cadmium, and Zinc via Modified Pencil Graphite Electrodes

Pencil graphite electrode (PGE) modified with MWCNT and Bi³⁺ (MWCNT/Bi/PGE) was utilized in simultaneous analysis of Pb²⁺, Cd²⁺, and Zn²⁺. Surface and electrochemical characteristics of MWCNT/Bi/PGE were investigated via SEM, cyclic voltammetry, electrochemical impedance spectroscopy, and FTIR measurements. Even though modification with MWCNT did not improve the electroactive surface area, it significantly decreased the charge transfer resistance. Furthermore, modification with Bi³⁺ significantly increased the sensitivity. Finally, MWCNT/Bi/PGE exhibited the highest sensitivity and reproducibility compared to PGE and PGE modified with only MWCNT. MWCNT/Bi/PGE provided LOD values of 0.27, 0.43, and 1.63 μg L⁻¹, and linear ranges of 1–80, 5–80, and 10–80 μg L⁻¹ for Pb²⁺, Cd²⁺, and Zn²⁺, respectively. Proposed modification method offers effective electroanalytical performance with low time consumption and cost for the analyst.     

Metallchelate ungesättigter geminaler Dichalcogenoliganden mit gemischten S,Se-Ligatoren Kristall- und Molekülstruktur von Tetra-n-butylammonium-bis(1,1-dicyanoethylen-2,2-thioselenolato)nickelat(II), [(n-C4H9)4N]2[Ni(SSeC?C(CN)2)2]

Metal Chelates of Unsaturated Geminal Dichalcogeno Ligands Containing S as well as Se Ligators. Crystal and Molecular Structure of Tetra-n-butylammonium-bis(1,1-dicyanoethylene-2,2-thioselenolato)nickelate(II), [(n-C₄H₉)₄N]₂[Ni(SSeC? C(CN)₂)₂] Synthesis and properties of chelates of the thioseleno ligands 1,1-dicyanoethylene-2,2-thioselenolate (bis-chelates with Ni²⁺, Pd²⁺, Pt²⁺, Cu²⁺, Au³⁺, Zn²⁺, Cd²⁺, Se²⁺, Te²⁺, UO₂²⁺; tris-chelate mit Cr³⁺, Fe³⁺, Co³⁺, Rh³⁺, In³⁺; 1:1-chelate mit Cu⁺, Au⁺), cyanthioselenocarbimate (bis-chelates with Ni²⁺, Pd²⁺) and 0-β-methoxyethyl-thioselenocarbonate (bis-chelates with Ni²⁺, Pd²⁺, Pt²⁺, Zn²⁺; tris-chelate mit Cr³⁺, Co³⁺, Rh³⁺) are reported. The X-ray crystal structure of [(n-C₄H₉)₄N]₂[Ni(SSeC? C(CN)₂)₂] shows a planar NiS₂Se₂ arrangement. From the space group P2₁/c (a = 14,043(1) Å, b = 8.704(1) Å, c = 20.647(2) Å, β = 108.56(1)°) and Z = 2 follows a trans position of the thioseleno ligands. The same magnitude of the C–S and C–Se distance refers to a hindrance of the equalization of the bonding in the chelate. The structure is compared with those of similar compounds.