Acceleration of laser-induced formation of gold nanoparticles in a poly(vinyl alcohol) film

Gold nanoparticles (AuNps) were fabricated in a poly(vinyl alcohol) (PVA) film using the photochemically generated benzophenone ketyl radical and PVA radical by laser irradiation as a reducing agent. The measurements of the surface plasmon band of AuNps indicated that AuNps continued growing in the PVA film for several hours or days after the laser irradiation. The formation process of AuNps in the PVA film was investigated by using laser flash photolysis and UV-vis absorption spectroscopy. Additive doping (formic acid or sodium 2-mercaptoethanesulfonate) in the PVA film dramatically accelerated or inhibited the formation rate of the AuNps, respectively. The doping of formic acid accelerated the formation rate of the AuNps by a factor of 10-20. On the contrary, doping of 2-mercaptoethanesulfonate inhibited the formation of AuNps. The mechanisms of the acceleration and inhibition were investigated by using laser flash photolysis. The effects of additives on the formation process of AuNps are discussed.     

Development of a histidine-targeted spectrophotometric sensor using Ni(II)NTA-functionalized Au and Ag nanoparticles

An antibody-free diagnostic reagent has been developed based on the aggregation-induced colorimetric change of Ni(II)NTA-functionalized colloidal gold and silver nanoparticles. This diagnostic strategy utilizes the high binding affinity of histidine-rich proteins with Ni(II)NTA to capture and cross-link the histidine-rich protein mimics with the silver and gold nanoparticles. In model studies, the aggregation behavior of the Ni(II)NTA nanoparticles was tested against synthetic targets including charged poly(amino acid)s (histidine, lysine, arginine, and aspartic acid) and mimics of Plasmodium falciparum histidine-rich protein 2 (pfHRP-II). Aggregation of the nanoparticle sensor was induced by all of the basic poly(amino acid)s including poly(l-histidine) within the pH range (5.5-9.0) tested, which is likely caused by the coordination between the multivalent polymer target and Ni(II)NTA groups on multiple particles. The peptide mimics induced aggregation of the nanoparticles only near their pK(a)'s with higher limits of detection. In addition, monomeric amino acids do not show any aggregation behavior, suggesting that multiple target binding sites are necessary for aggregation. Long-term stability studies showed that gold but not silver nanoparticles remained stable and exhibited similar aggregation behavior after 1 month of storage at room temperature and 37 °C. These results suggest that Ni(II)NTA gold nanoparticles could be further investigated for use as a sensor to detect histidine-rich proteins in biological samples.     

Synthesis of a nanocomposite containing a water‐soluble polythiophene derivative and gold nanoparticles

This paper reports on a facile method for synthesizing gold nanoparticles (AuNps) with diameter around 5 nm encapsulated with water‐soluble polythiophene sulfonate poly[2‐(3‐thienyl)ethyloxy‐4‐butylsulfonate] sodium salt (PTS) and their physical–chemical characterization. The synthesis of hybrid materials of polythiophene derivatives and gold nanoparticles is a way to improve the polymer properties, mainly in application for chemical and optical sensing platforms. The AuNps were prepared by reducing gold salt with acid aqueous sodium citrate by the Turkvich method in the presence of PTS, and both PTS and citrate helped to stabilize the AuNps. The suspensions of AuNp:PTS presented good chemical and photostability for long period of storage. The nanoparticles encapsulated with the polymer presented smaller diameters than those obtained using only sodium citrate, according to scanning electron microscopy images. The AuNps obtained were used for fabrication LbL films with commercial chitosan, which were characterized by impedance spectroscopy measurements. The results showed that the charge transfer resistance values (R_ct) decrease as the average diameter of the AuNps decreases and the proportion of PTS increases in the nanocomposite. Such increase of the nanocomposite conductivity, given by the low values of R_ct, indicates that the novel film architecture developed is promising for chemical sensing applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1245–1254     

Preparation of Polymer Nanofibers Containing Silver Nanoparticles by Using Poly(N‐vinylpyrrolidone)

Summary: Poly(N‐vinylpyrrolidone) (PVP) was used in two methods to prepare polymer nanofibers containing Ag nanoparticles. The first method involved electrospinning the PVP nanofibers containing Ag nanoparticles directly from the PVP solutions containing the Ag nanoparticles. N,N‐Dimethylformamide was used as a solvent for the PVP as well as a reducing agent for the Ag⁺ ions in the PVP solutions. In the second method, poly(vinyl alcohol) (PVA) aqueous solutions were electrospun with 5 wt.‐% of the PVP containing Ag nanoparticles. The Ag nanoparticles were evenly distributed in the PVA nanofibers. PVP containing Ag nanoparticles could be used to introduce Ag nanoparticles to other polymer nanofibers that are miscible with PVP.

TEM image of a PVA nanofiber electrospun with 5 wt.‐% of the PVP containing Ag nanoparticles.     

Grafting a monolayer of superparamagnetic cyanide-bridged coordination nanoparticles on Si(100)

The grafting of a monolayer of 6 nm superparamagnetic cyanide-bridged CsNiCr nanoparticles was achieved on a Ni(II)-functionalized Si(100) substrate; magnetic studies reveals that the grafted nanoparticles are nearly magnetically isolated within the monolayer.     

Ni(II)‐NTA Modified Poly(ethylene imine) Glycopolymers: Physicochemical Properties and First In Vitro Study of Polyplexes Formed with HIV‐Derived Peptides

Alternative delivery entities are desirable in immunotherapies in which polyplexes are widely formed by electrostatic interactions to induce cellular uptake processes for bioactive molecules. In our study, biocompatible Ni(II)‐nitrilo(triacetic acid)‐modified poly(ethylene imine)‐maltose ( Ni‐NTA‐DG ) is realized and evaluated as complexation agent against His‐tagged peptides using fluorescence polarization and dynamic light scattering. The polyplexes are stable until a pH of 6.5–6.0, and also up to 50 mM of imidazole. A first uptake approach shows that polyplexes lead to an increase in peptide uptake in monocyte‐derived immature dendritic cells. In summary, Ni‐NTA‐DG represents a promising (delivery) platform for forthcoming in vitro applications.

     

Synthesis, spectral and electrochemical studies of Cu(II) and Ni(II) complexes with new N2O2 ligands: a new precursor capable of depositing copper nanoparticles using thermal reduction

Cu(II) and Ni(II) complexes of the general type [M(N2O2)] are described. The N2O2 ligands used are [N,N'-bis(2-hydroxy-6-methoxybenzylidene)propane-1,3-diamine] (HOMeSalpn) and [N,N'-bis(2-hydroxy-6-methoxybenzylidene)propane-1,2-diamine (HOMeSalpr). These complexes have been characterized by IR, UV-vis, CV, TG-DTA and 1H NMR spectroscopy. The electrochemical behavior of these complexes at a glassy carbon electrode in acetonitrile solution indicates that the first reduction process corresponding to Cu(II)-Cu(I) and Ni(II)-Ni(I) is electrochemically irreversible. The new copper complexes have been applied for the preparation of copper nanoparticles using non-ionic surfactant (Triton X-100) by thermal reduction. The copper nanoparticles with average size of 48nm were formed by thermal reduction of [N,N'-bis(2-hydroxy-6-methoxybenzylidene)propane-1,3-diamine]copper(II) in the presence of triphenylphosphine thus releasing the reduced copper and affording the high-purity copper nanoparticles.     

Acireductone dioxygenase- (ARD-) type reactivity of a nickel(II) complex having monoanionic coordination of a model substrate: product identification and comparisons to unreactive analogues

A mononuclear Ni(II) complex ([(6-Ph2TPA)Ni(PhC(O)C(OH)C(O)Ph)]ClO4 (1)), supported by the 6-Ph2TPA chelate ligand (6-Ph2TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine) and containing a cis-beta-keto-enolate ligand having a C2 hydroxyl substituent, undergoes reaction with O2 to produce a Ni(II) monobenzoate complex ([(6-Ph2TPA)Ni(O2CPh)]ClO4 (3)), CO, benzil (PhC(O)C(O)Ph), benzoic acid, and other minor unidentified phenyl-containing products. Complex 3 has been identified through independent synthesis and was characterized by X-ray crystallography, 1H NMR, FAB-MS, FTIR, and elemental analysis. A series of cis-beta-keto-enolate Ni(II) complexes supported by the 6-Ph2TPA ligand ([(6-Ph2TPA)Ni(PhC(O)CHC(O)Ph)]ClO4 (4), [(6-Ph2TPA)Ni(CH3C(O)CHC(O)CH3)]ClO4 (5), and [(6-Ph2TPA)Ni(PhC(O)CHC(O)C(O)Ph) (6)) have been prepared and characterized. While these complexes exhibit structural and/or spectroscopic similarity to 1, all are unreactive with O2. The results of this study are discussed in terms of relevance to Ni(II)-containing acireductone dioxygenase enzymes, as well as in the context of recently reported cofactor-free, quercetin, and beta-diketone dioxygenases.     

Epidermal cellular response to poly(vinyl alcohol) nanofibers containing silver nanoparticles

A heat-treated PVA nanofibrous matrix containing silver (Ag) was prepared by electrospinning an aqueous 10 wt% PVA solution and followed by heat treatment at 150 °C for 10 min. The average diameter of the as-spun and heat-treated PVA nanofibers was 330 nm. The heat-treated PVA nanofibrous matrix containing Ag was irradiated with UV light to transform the Ag ions in the nanofibrous matrix into Ag nanoparticles. The in vitro cytotoxicity of the Ag ions and/or nanoparticles on normal human epidermal keratinocytes (NHEK) and fibroblasts (NHEF) cultures was examined. The PVA nanofibrous matrix containing Ag showed slightly higher level of attachment and spreading in the early stage culture (1 h) than the PVA nanofibers without Ag (control). However, compared with the PVA nanofibers without Ag, the heat-treated and UV-irradiated PVA nanofibers, containing mainly Ag ions and nanoparticles, respectively, showed reduced cell attachment and spreading. This shows that both Ag ions and Ag nanoparticles are cytotoxic to NHEK and NHEF. There was no significant difference in cytotoxicity to NHEK and NHEF between Ag ions and Ag nanoparticles. NHEF appeared to be more sensitive to Ag ions or particles than NHEK. In addition, the residual nitrate ions (NO₃⁻) in the PVA nanofibers had an adverse effect on the culture of both cells.     

Tridentate facial ligation of tris(pyridine-2-aldoximato)nickel(II) and tris(imidazole-2-aldoximato)nickel(II) To generate NiIIFeIIINiII, MnIIINiII, NiIINiII, and ZnIINiII and the electrooxidized MnIVNiII, NiIINiIII, and ZnIINiIII species: a magnetostructural, electrochemical, and EPR spectroscopic study

Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) with three facially disposed pendent oxime O atoms has been utilized to generate the said complexes. Complex 1 contains metal centers in a linear arrangement, as is revealed by X-ray diffraction. Complexes were characterized by various physical methods including cyclic voltammetry (CV), variable-temperature (2-290 K) magnetic susceptibility, electron paramagnetic resonance (EPR) measurements, and X-ray diffraction methods. Binuclear complexes 2-6 are isostructural in the sense that they all contain a metal ion in a distorted octahedral environment MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) geometry. Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural Ni(II)2 complexes, 3a-c, and 4, demonstrates the effects of the remote substituents on the spin coupling. The electrochemical measurements CV and square wave voltammograms (SQW) reveal two reversible metal-centered oxidations, which have been assigned to the Ni center ligated to the oxime N atoms, unless a Mn ion is present. Complex 2, Mn(III)Ni(II), exhibits a reduction of Mn(III) to Mn(II) and two subsequent oxidations of Mn(III) and Ni(II) to the corresponding higher states. These assignments of the redox processes have been complemented by the X-band EPR measurements. That the electrooxidized species [3a]+, [3b]+, [3c]+, and [4]+ contain the localized mixed-valent NiIINiIII system resulting from the spin coupling, a spin quartet ground state, S(t) = 3/2, has been confirmed by the X-band EPR measurements.     

镍, 锌, 钴(II)-N-(间甲苯基)亚氨基二乙酸-氮三乙酸的量热研究

使用改进的RD-1型热导式量热计测量了镍(II), 锌(II),钴(II)-N-(间甲苯基)亚氨基二乙酸-氮三乙酸三元配合物的生成焓, 发现其大小按金属离子来说符合Irving-William序列。利用配体的多环水化结构等讨论了该三元配合物的生成焓和相应的二元配合物的生成焓, 同时求得了上述三元体系的热力学参数, 指出上述三元体系的生成熵是导致这些三元体系具有较大稳定性的根本原因。     

Pd(II)-mediated assembly of porphyrin channels in bilayer membranes

A membrane-spanning bis(meso-3-pyridyl) porphyrin 1 has been synthesized, embedded in EYPC vesicles, and upon Pd(II) addition has been shown to form ionophores that allow the passage of anionic 5/6-carboxyfluorescein through membranes. The geometric matching of bis(meso-3-pyridyl) porphyrin 1 and trans-Pd(II) was designed to give a cyclic porphyrin trimer [PdCl(2)(1)](3). However, solution-phase studies showed that PdCl(2)(PhCN)(2) cross linked 1 into linear oligomers at porphyrin concentrations above 10 mM, although the formation of cyclic species was inferred from studies at concentrations below 2 μM. Fluorescence titrations showed that embedding porphyrin 1 in bilayers greatly reduced its affinity for Pd(II), but the combination of porphyrin 1 and Pd(II) gave an ionophoric species that increased the rate of 5/6-carboxyfluorescein (5/6-CF) transit through the phospholipid bilayer 12-fold. A maximum in the 5/6-CF release rate was observed at a Pd(II) concentration of 4 μM, and the application of a solution-phase binding model to the membrane phase showed that this peak in ionophoric activity corresponded to the greatest extent of porphyrin oligomerization. Further studies suggested these Pd(II)/porphyrin oligomers transported 5/6-CF via a channel mechanism.     

Fast Simultaneous Adsorptive Stripping Voltammetric Determination of Ni(II) and Co(II) at Lead Film Electrode Plated on Gold Substrate

A fast adsorptive stripping voltammetric procedure for simultaneous determination of Ni(II) and Co(II) in the presence of nioxime as a complexing agent at an in situ plated lead film electrode was described. The time of determination of these ions was shortened due to the application of gold as a substrate for lead film. At gold substrate lead film formation and accumulation of Ni(II) and Co(II) complexes with nioxime proceeds simultaneously. To obtain a stable signals for both ions a simple procedure of activation of the electrode was proposed. Calibration graphs for an accumulation time of 20 s were linear from 5×10^?9 to 1×10^?7 mol L^?1 and from 5×10^?10 to 1×10^?8 mol L^?1 for Ni(II) and Co(II), respectively. The procedure with the application of a lead film electrode on a gold substrate was validated in the course of Ni(II) and Co(II) determination in certified reference materials.     

Radiation synthesis of copper sulphide/poly(vinyl alcohol) nanocomposites films: an efficient and reusable catalyst for p-nitrophenol reduction

ABSTRACT

Copper sulphide nanoparticles (CuS NPs) were in situ synthesised via irradiation process, using Poly (vinyl alcohol) (PVA) as host polymeric matrices. The as-prepared CuS/PVA nanocomposite films were characterised by X-ray diffraction (XRD) spectroscopy, ultraviolet-visible (UV-VIS) spectroscopy, Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Both UV-VIS spectra and X-ray diffraction patterns confirmed the formation of CuS nanoparticles. The FTIR spectrum indicates the coordination between CuS nanoparticles and the OH groups of the PVA chains. The TEM image showed that the obtained CuS nanoparticles have spherical shape, monodispersed and uniform particle size distribution. The CuS/PVA nanocomposite film was successfully applied in the reduction of p-nitrophenol into p-aminophenol as a catalyst using NaBH₄ as reducing agent. The catalytic test indicates that CuS/PVA nanocomposite film has high activity for the conversion of P-NP into P-AP and effectively recycled and reused for several times.     

Application of lead film electrode for simultaneous adsorptive stripping voltammetric determination of Ni(II) and Co(II) as their nioxime complexes

An adsorptive stripping voltammetric (AdSV) procedure for simultaneous determination of Ni(II) and Co(II) in the presence of nioxime as a complexing agent at an in situ plated lead film electrode was described. The Co(II) signal was enhanced by exploitation of the catalytic process in the presence of nitrite. Ni(II) and Co(II) signals are better separated than in the case of bismuth film electrodes. Calibration graphs for an accumulation time of 120 s are linear from 1 × 10⁻⁹ to 1 × 10⁻⁷ mol L⁻¹ and from 1 × 10⁻¹⁰ to 5 × 10⁻⁹ mol L⁻¹ for Ni(II) and Co(II), respectively. The proposed procedure was applied for Ni(II) and Co(II) determination in water certified reference materials.     

Synthesis of Some Polymer‐Metal Complexes and Elucidation of their Structures

In this study, the nine coordination polymers of Fe(III), Co(II) and Ni(II) salts have been synthesized using polyacrylamide (PAA), polt(ethylene glycol) (PEG) and poly(vinyl alcohol) (PVA) and their structures were characterized by magnetic and conductivity measurements, ultraviolet‐visible (UV‐VIS), FTIR spectroscopy and thermogravimetric analysis (TGA). The structures of Fe(III) complexes in the all coordination polymers were found as tetrahedral. The structures of PAA‐Co(II) coordination polymer was determined as octahedral geometry whereas PEG‐Co(II) and PVA‐Co(II) complexes showed as tetrahedral structure. PAA‐Ni(II) and PEG‐Ni(II) complexes have octahedral geometry, whereas PVA‐Ni(II) has a square planar structure. Besides, the stress‐strain experiments of PVA‐metal coordination polymers obtained rubber‐like structure were carried out and the value of breaking‐strain of PVA‐Ni(II) complex was found to be about 17% of vulcanized natural rubber. The conductivities of the resulting polymer‐metal complexes were measured by four‐probe technique and were found in the range 10^?5?10^?6 Scm^?1. Thus, it was suggested that they can be used in the field potential application of conducting polymers. TGA results revealed that among the complexes PEG‐Fe(III) and PVA‐Fe(III) complexes have the highest thermally stable.     

Crystal environments probed by EPR spectroscopy. Variations in the EPR spectra of Co(II)(octaethylporphyrin) doped in crystalline diamagnetic hosts and a reassessment of the electronic structure of four-coordinate cobalt(II)

The powder and single-crystal EPR spectra of Co(II)(OEP) (OEP is the dianion of octaethylporphyrin) doped into a range of diamagnetic crystals including simple four-coordinate hosts, H(2)(OEP), the triclinic B form of Ni(II)(OEP), the tetragonal form of Ni(II)(OEP) and Zn(II)(OEP); five-coordinate hosts, micro-dioxane)[Zn(II)(OEP)](2) and (py)Zn(II)(OEP); six-coordinate hosts, (py)(2)Zn(II)(OEP) and (py)(2)Mg(II)(OEP); and hosts containing fullerenes, C(60).2Zn(II)(OEP).CHCl(3), C(70).Ni(II)(OEP).C(6)H(6).CHCl(3), and C(60).Ni(II)(OEP).2C(6)H(6) have been obtained and analyzed. Spectra were simulated using a program that employed the exact diagonalization of the 16 x 16 complex spin Hamiltonian matrix. The EPR spectra of these doped samples are very sensitive to the environment within each crystal with the crystallographic site symmetry determining whether axial or rhombic resonance patterns are observed. For Co(II)(OEP) doped into tetragonal Ni(II)(OEP) (which displays a very large g( perpendicular ) of 3.405 and a very small g( parallel ) of 1.544) and several other crystals containing four-coordinate metal sites, the g components could not be fit using existing theory with the assumption of the usual z(2) ground state. However, reasonable agreement of the observed EPR parameters could be obtained by assuming that the unpaired electron resides in an xy orbital in the four-coordinate complexes.     

Synthesis, structure, and magnetic properties of (6-9)-nuclear Ni(II) trimethylacetates and their heterospin complexes with nitroxides

New polynuclear nickel trimethylacetates [Ni6(OH)4(C5H9O2)8(C5H10O2)4] (6), [Ni7(OH)7(C5H9O2)7(C5H10O2)6(H2O)] x 0.5 C6H14 x 0.5 H2O (7), [Ni8(OH)4(H2O)2(C5H9O2)12] (8), and [Ni9(OH)6(C5H9O2)12(C5H10O2)4] x C5H10O2 x 3 H2O (9), where C5H9O2 is trimethylacetate and C5H10O2 is trimethylacetic acid, have been found. Their structures were determined by X-ray crystallography. Because of their high solubility in low-polarity organic solvents, compounds 6-9 reacted with stable organic radicals to form the first heterospin compounds based on polynuclear Ni(II) trimethylacetate and nitronyl nitroxides containing pyrazole (L(1)-L(3)), methyl (L(4)), or imidazole (L(5)) substituent groups, respectively, in side chain [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L(1))2(H2O)] x 0.5 C6H14 x H2O (6+1a), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L2)2(H2O)] x H2O (6+1b), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L(3))2(H2O)] x H2O (6+1c), [Ni6(OH)3(C5H9O2)9(C5H10O2)4(L(4))] x 1.5 C6H14 (6'), and [Ni4OH)3(C5H9O2)5(C5H10O2)4(L(5))] x 1.5 C7H8 (4). Their structures were also determined by X-ray crystallography. Although Ni(II) trimethylacetates may have varying nuclearity and can change their nuclearity during recrystallization or interactions with nitroxides, this family of compounds is easy to study because of its topological relationship. For any of these complexes, the polynuclear framework may be derived from the [Ni6] polynuclear fragment {Ni6(mu4-OH)2(mu3-OH)2(mu2-C5H9O2-O,O')6(mu2-C5H9O2-O,O)(mu4-C5H9O2-O,O,O',O')(C5H10O2)4}, which is shaped like an open book. On the basis of this fragment, the structure of 7-nuclear compounds (7 and 6+1a-c) is conveniently represented as the result of symmetric addition of other mononuclear fragments to the four Ni(II) ions lying at the vertexes of the [Ni6] open book. The 9-nuclear complex is formed by the addition of trinuclear fragments to two Ni(II) ions lying on one of the lateral edges of the [Ni6] open book. This wing of the 9-nuclear complex preserves its structure in another type of 6-nuclear complex (6') with the boat configuration. If, however, two edge-sharing Ni(II) ions are removed from [Ni6] (one of these lies at a vertex of the open book and the other, on the book-cover line), we obtain a 4-nuclear fragment recorded in the molecular structure of 4. Twinning of this 4-nuclear fragment forms highly symmetric molecule 8, which is a new chemical version of cubane.     

Utilization of olive pomace in nano MgO modification for sorption of Ni(II) and Cu(II) metal ions from aqueous solutions

Magnesium oxide nanoparticles were synthesized and modified by olive pomace (NMOOP700) as a novel sorbent and characterized using Fourier Transform Infrared Spectra, Scanning Electron Microscope, Transmission Electron Microscope, X-ray Diffraction, Differential Thermal Analysis and Thermal Gravimetric Analysis. Sorption of Cu (II) or Ni (II) ions were achieved taking into account important parameters including initial pH of the medium, contact time, initial metal ion concentration and temperature. A comparative study between Magnesium oxide nanoparticles and NMOOP700 material for the sorption of Cu (II) or Ni (II) ions was implemented. The obtained data revealed that the sorption process is significantly improved using NMOOP700. The monolayer capacity of Ni (II) and Cu (II) metal ions on NMOOP700 at pH 5 were found to be 149.93 ± 4.4 and 186.219 ± 6.3 mg/g, respectively. Findings of the present work highlight the potential use of NMOOP700 as a novel and effective sorbent material for the removal of Cu (II) or Ni (II) ions from the liquid phase.     

Selective determination of Ni(II) and Co(II) by flow injection analysis and adsorptive cathodic stripping voltammetry on a wall jet mercury film electrode

Ni(II) and Co(II) have been determined simultaneously by means of adsorptive cathodic stripping voltammetry (AdCSV) in a computerised flow injection system. The working electrode was a glassy carbon disk that was fitted in a wall-jet flow cell. The electrode was initially electrochemically coated with a mercury film at -1.0 V by injecting a Hg(II) solution in the flow stream. Then, the sample, containing Ni(II) and Co(II), was mixed on-line with a solution containing dimethylgyoxime (DMG) at pH 9 in order to selectively complex the metal ions and was injected in the flow system. After a number of successive injections during which accumulation took place under controlled potentiostatic conditions, the surface-bound complexes were reduced in ammonia buffer at pH 9 by a cathodic scan of the potential of the working electrode in the square wave mode and the current-potential response was recorded. Finally, the electrode surface was regenerated by a potentiostatic polarisation at -1.4 V in the same buffer. The apparatus could be easily converted for continuous flow accumulation in order to increase the sensitivity; in this mode of operation, instead of performing discrete injections, the sample was continuously pumped through the cell. Various parameters associated with the preconcentration, stripping and regeneration steps were optimised for the determination of Ni(II) and Co(II). The selectivity of the method was demonstrated for the analysis of high purity iron; the accuracy for the determination of Ni(II) and Co(II) was 11 and 3%, respectively while the coefficient of variation was 10 and 8%, respectively.