Catalytic activity of polymer-bound Ru(III)-EDTA complex

Chloromethylated styrene-divinylbenzene copolymer was chemically modified with ethylenediaminetetraacetic acid ligand. Catalytically active polymer containing Ru(III) moieties were synthesized from this polymeric ligand. They were characterized using FTIR, UV-vis, SEM, ESR and TGA. Other physico-chemical properties such as bulk density, surface area, moisture content and swelling behaviour in different solvents were also studied. The polymer bound complex was used to study hydrogenation of 1-hexene ton-hexane under mild conditions. Influence of [1-hexene], [catalyst], temperature and nature of the solvent on the rate of the reaction was investigated. A rate expression is proposed based on the observed initial rate data. Recycling efficiency of the catalyst has also been studied.     

An Ir(III) complex chemosensor for the detection of thiols

In this study, we report the use of a cyclometalated luminescent iridium(III) complex for the visualization of thiols. The detection of glutathione (GSH) by complex 1 is achieved through the reduction of its phendione N^N donor, which influences the metal-to-ligand charge-transfer (MLCT) of the complex. Complex 1 produced a maximum threefold luminescence enhancement at 587 nm in response to GSH. The linear detection range of 1 for GSH is between 0.2 and 2 M equivalents of GSH, with a detection limit of 1.67 μM. Complex 1 also displays good selectivity for thiols over other amino acids.     

Mossbauer evidence for Ru(IV) and Ru(II) in TiO2

The Mössbauer absorption of the 89.4 keV line of ⁹⁹Ru has been measured at 4.2 K for samples of Ru in TiO₂ and in TiO₂ doped with Ta. We deduce that Ru replaces Ti substitutionally in TiO₂ as Ru(IV) and that no delocalisation of the four Ru(IV) 4d electrons occurs. If the donor Ta is added to the system, the ion Ru(II) is formed, demonstrating that Ru behaves as an acceptor in TiO₂.     

Oligonucleotide-based fluorescence probe for sensitive and selective detection of mercury(II) in aqueous solution

In this paper we unveil a new homogeneous assayusing TOTO-3 and the polythymine oligonucleotide T 33for the highly selective and sensitive detection of Hg (2+) in aqueous solution. The fluorescence of TOTO-3 is weak in the absence or presence of randomly coiled T 33. After T 33 interacts specifically with Hg (2+) ions through T-Hg (2+)-T bonding, however, its conformation changes to form a folded structure that preferably binds to TOTO-3. As a result, the fluorescence of a mixture of T 33 and TOTO-3 increases in the presence of Hg (2+). Our data from fluorescence polarization spectroscopy, capillary electrophoresis with laser-induced fluorescence detection, circular dichroism spectroscopy, and melting temperature measurements confirm the formation of folded T 33-Hg (2+) complexes. Under optimum conditions, the TOTO-3/T 33 probe exhibited a high selectivity (>or=265-fold) toward Hg (2+) over other metal ions, with a limit of detection of 0.6 ppb. We demonstrate the practicality of this TOTO-3/T 33 probe for the rapid determination of Hg (2+) levels in pond water and in batteries. This approach offers several advantages, including rapidity (<15 min), simplicity (label-free), and low cost.     

Tris(2-aminoethyl) amine functionalized silica gel for solid-phase extraction and preconcentration of Cr(III), Cd(II) and Pb(II) from waters

A new tris(2-aminoethyl) amine (TREN) functionalized silica gel (SG-TREN) was prepared and investigated for selective solid-phase extraction (SPE) of trace Cr(III), Cd(II) and Pb(II) prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Identification of the surface modification was characterized and performed on the basis of FT-IR. The separation/preconcentration conditions of analytes were investigated, including effects of pH, the shaking time, the sample flow rate and volume, the elution condition and the interfering ions. At pH 4, the maximum adsorption capacity of Cr(III), Cd(II) and Pb(II) onto the SG-TREN were 32.72, 36.42 and 64.61 mg g(-1), respectively. The adsorbed metal ions were quantitatively eluted by 5 mL of 0.1 mol L(-1) HCl. Common coexisting ions did not interfere with the separation. According to the definition of International Union of Pure and Applied Chemistry, the detection limits (3sigma) of this method for Cr(III), Cd(II) and Pb(II) were 0.61, 0.14 and 0.55 ng mL(-1), respectively. The relative standard deviation under optimum conditions is less than 4.0% (n=11). The application of this modified silica gel to preconcentration trace Cr(III), Cd(II) and Pb(II) of two water samples gave high accurate and precise results.     

Chromium(III) porphyrin as a selective ionophore in a salicylate-selective membrane electrode

The construction, potentiometric response properties, and applications of a novel ion-selective electrode with high selectivity toward salicylate are described. Chromium(III) tetraphenylporphyrin chloride was used as ion carrier into plasticized PVC membrane. This ionophore is capable of serving as both a positively charged and neutral carrier, depending on the pH of the sample solution. The influence of several variables was investigated to optimize the potentiometric response and selectivity of the electrode. The resulting electrode demonstrates a near-Nernstian response over a wide range of salicylate concentration (10(-6)-10(-1) M). This electrode has a fast response time and micromolar detection limit and could be used over a wide pH range (3-9). The proposed electrode showed very high selectivity for salicylate over a number of common inorganic and organic anions. The specific interaction of salicylate with the central metal of porphyrin is described based on UV-visible absorption spectra. The electrode was successfully applied to the determination of salicylate in pharmaceutical preparations and clinical samples.     

A Schiff base complex of Zn(II) as a neutral carrier for highly selective PVC membrane sensors for the sulfate ion

Novel polymeric membrane (PME) and coated graphite (CGE) sulfate-selective electrodes based on a recently synthesized Schiff base complex of Zn(II) were prepared. The electrodes reveal a Nernstian behavior over wide SO4(2-) ion concentration ranges (5.0 x 10(-5)-1.0 x 10(-1) M for PME and 1.0 x 10(-7)-1.0 x 10(-1) M for CGE) and very low detection limits (2.8 x 10(-5) M for PME and 8.5 x 10(-8) M for CGE). The potentiometric response is independent of the pH of the solution in the pH range 3.0-7.0. The electrodes manifest advantages of low resistance, very fast response, and, most importantly, good selectivities relative to a wide variety of other anions. In fact, the selectivity behavior of the proposed SO4(2) ion-selective electrodes shows a great improvement compared to the previously reported electrodes for sulfate ion. The electrodes can be used for at least 3 months without any appreciable divergence in potentials. The electrodes were used as an indicator electrode in the potentiometric titration of sulfate and barium ions and in the determination of iron in ferrous sulfate tablets.     

Stable tris(2,2'-bipyridine)ruthenium(III) for chemiluminescence detection

Two exceedingly stable [Ru(bipy)(3)](3+) reagents were prepared by dissolving either [Ru(bipy)(3)](ClO(4))(2) in acetonitrile (containing 0.05 M HClO(4)) or [Ru(bipy)(3)]Cl(2)·6H(2)O in 95:5 glacial acetic acid-acetic anhydride (containing 0.05 M H(2)SO(4)) followed by oxidation with PbO(2). These conveniently prepared solutions provide highly reproducible chemiluminescence detection over long periods of analysis, avoiding the need for recalibration or preparation of fresh reagent solutions and without the complications associated with online chemical or electrochemical oxidations. The reagent prepared in acetonitrile produced much greater signal intensities with a range of analytes and was deemed most suitable for high-performance liquid chromatography (HPLC) with postcolumn chemiluminescence detection.     

Economical, green synthesis of fluorescent carbon nanoparticles and their use as probes for sensitive and selective detection of mercury(II) ions

The present article reports on a simple, economical, and green preparative strategy toward water-soluble, fluorescent carbon nanoparticles (CPs) with a quantum yield of approximately 6.9% by hydrothermal process using low cost wastes of pomelo peel as a carbon source for the first time. We further explore the use of such CPs as probes for a fluorescent Hg(2+) detection application, which is based on Hg(2+)-induced fluorescence quenching of CPs. This sensing system exhibits excellent sensitivity and selectivity toward Hg(2+), and a detection limit as low as 0.23 nM is achieved. The practical use of this system for Hg(2+) determination in lake water samples is also demonstrated successfully.     

Genosensor based on a platinum(II) complex as electrocatalytic label

Voltammetric genosensors on streptavidin-modified screen-printed carbon electrodes (SPCEs) for the detection of virulence nucleic acid determinants of pneumolysin (ply) and autolysin (lytA) genes, exclusively present on the genome of the human pathogen Streptococcus pneumoniae, were described. The oligonucleotide probes were immobilized on electrochemically pretreated SPCEs through the streptavidin/biotin reaction. After that, the hybridization reaction was carried out with labeled complementary targets on the electrode surface. The ply and lytA targets were labeled using the universal linkage system, which consists of the use of a platinum(II) complex that acts as coupling agent between targets and a, usually fluorescent, molecule label. In this case, the platinum(II) complex acts as a label itself because the analytical signal is achieved by measuring chronoamperometrically the current generated by the hydrogen evolution catalyzed by platinum. In nonstringent experimental conditions, these genosensors can detect 24.5 fmol of 20-mer oligonucleotide target and discriminate between a complementary oligo and an oligo with a three-base mismatch. In presence of 25% formamide in the hybridization buffer, a single-base mismatch on the oligonucleotide target can be detected.     

Chromatographic detection using tris(2,2'-bipyridyl)ruthenium(III) as a fluorogenic electron-transfer reagent

Tris(2,2'-bipyridyl)ruthenium can be excited to fluorescence by visible light (lambda abs 454 nm, lambda em 607 nm) when in the M(II) oxidation state, but not in the M(III) state. A novel chromatographic detection method using the non-fluorescent M(III) form of the complex as a postcolumn fluorogenic reagent is demonstrated. The M(III) form is a powerful oxidizing agent (E degree = 1.27 V vs NHE, 1.05 V vs Ag/AgCl). The M(III) reagent is generated on-line from the M(II) form of the complex by a highly efficient porous carbon electrode and then reacted briefly with chromatographic effluent; the M(II) created by electron transfer from oxidation-susceptible analytes is then detected by fluorescence. The fluorescence detector can be calibrated for number of electrons transferred by injection of either M(II) or an oxidative standard such as ferrocyanide. It is hoped that this redox-based detection scheme will provide an alternative to electrochemical detection. Among the advantages are freedom from surface fouling and the potential for extremely low detection limits. The scheme was applied to detection of the peptide dynorphin A and several of its fragments. Dynorphin A contains tyrosine at the N-terminus (position 1) and tryptophan in position 15; these amino acid residues are susceptible to oxidation and peptides containing them can be detected on that basis. Flow injection testing of the model compounds Tyr-Gly-Gly-Phe-Leu and Gly-Gly-Trp-Gly indicated that tyrosine transferred approximately 1 electron to the M(III) reagent and that tryptophan transferred approximately 4 electrons. Similar results were obtained from the chromatographic runs. Dynorphin A and six dynorphin A fragments containing the N-terminal tyrosine were detected easily at 100 nM concentration (14 pmol) using laser-induced fluorescence. As expected, one fragment that did not contain tryptophan or tyrosine was not detected. A mass detection limit of 80 fmol was estimated for the tyrosine-containing fragments.     

A new ion-selective electrode based on aluminium tungstate for Fe(III) determination in rock sample, pharmaceutical sample and water sample

An inorganic cation exchanger, aluminum tungstate (AT), has been synthesized by adding 0·1 M sodium tungstate gradually into 0·1 M aluminium nitrate at pH 1·2 with continuous stirring. The ion exchange capacity for Na⁺ ion and distribution coefficients of various metal ions was determined on the column of aluminium tungstate. The distribution studies of various metal ions showed the selectivity of Fe(III) ions by this cation exchange material. So, a Fe(III) ion-selective membrane electrode was prepared by using this cation exchange material as an electroactive material. The effect of plasticizers viz. dibutyl phthalate (DBP), dioctylphthalate (DOP), di-(butyl) butyl phosphate (DBBP) and tris-(2-ethylhexylphosphate) (TEHP), has also been studied on the performance of membrane sensor. It was observed that the membrane containing the composition AT: PVC: DBP in the ratio 2: 20: 15 displayed a useful analytical response with excellent reproducibility, low detection limit, wide working pH range (1–3·5), quick response time (15 s) and applicability over a wide concentration range of Fe(III) ions from 1 × 10⁻⁷ M to 1 × 10⁻¹ M with a slope of 20 ± 1 mV per decade. The selectivity coefficients were determined by the mixed solution method and revealed that the electrode was selective for Fe(III) ions in the presence of interfering ions. The electrode was used for atleast 5 months without any considerable divergence in response characteristics. The constructed sensor was used as indicator electrode in the potentiometric titration of Fe(III) ions against EDTA and Fe(III) determination in rock sample, pharmaceutical sample and water sample. The results are found to be in good agreement with those obtained by using conventional methods.     

Quaternary thiospinel CuCrTiS4 as an electroactive material for copper(II)-sensitive and selective electrode

CuCrTiS₄ was obtained by solid-state synthesis methods. The crystal structure of the quaternary phase was investigated by X-ray powder method and is described in the thiospinel structure (space group Fd¯3m) with the lattice parameter а = 0,99388(1) nm. Atomic parameters were refined in the isotropic approximation (R_I = 0.0465, R_P = 0.1060). The possibility of the use of this compound as an electroactive substance in graphite-paste electrodes for the measurement of Сu²⁺ ions was investigated. The electrodes exhibit a Nernstian response towards copper (II) ions with a cationic slope. The optimal electrode composition, detection limit (6 · 10^− 7 M), selectivity coefficient for major interfering elements, рН range and practical applicability of such electrodes were established.     

Electrical transport as a function of temperature in urea and cobalt (III)-urea complex

The temperature dependence of the electrical conductivity, and the voltage–current dependence of urea and its cobalt solid complex were determined. The values of the thermal activation energies indicate that the two compounds behave like semiconductors. The semiconducting properties of the ligand urea are due to the electron delocalization via -bond formation (C=NH,C=₂ ⁺) as well as the lone pair of electrons on the oxygen atoms of urea molecules. The high conductivity values of urea compared with those of its cobalt solid complex was suggested to be due to the ease of releasing the lone pair electrons on the oxygen atom as well as the hydrogen transfer during enol formation of urea molecules. The infrared, ultraviolet and visible absorption measurements were carried out to rationalize the mechanism of the conduction process in the investigated compounds.     

EDTA excess Zn(II) back-titration in the presence of 4-(2-pyridylazo)-resorcinol indicator and naphthol green beta as inert dye for determining Cr(III) as Cr(III)/EDTA complex: application of the method to a leather industry wastewater

The colour changes of 4-(2-pyridylazo)-resorcinol and naphthol green beta as new screening metallochromic indicator in back-titration of EDTA excess with Zn(II) to determine Cr(III)/EDTA complex was investigated with the help of tristimulus colorimetry. Specific colour discrimination (SCD) and L*, a*, b* 1976 parameters were successfully applied to evaluate the quality of colour transition at the end-point in non-alkaline media and in the presence of Zn(II) and Ca(II) which resulted in non-interfering species at 1x10(-3) M and 2x10(-3) M, respectively. The above concentrations are comparable with those used for Cr(III). Validation of the fast and accurate reported method was performed by atomic absorption spectroscopy. Moreover, the method was applied for determining Cr as Cr(III) in a wastewater effluent deriving from a leather industry.     

Zinc oxide-decorated multiwalled carbon nanotubes: a selective electrochemical sensor for the detection of Pb(II) ion in aqueous media

Journal of Materials Science: Materials in Electronics - Multiwalled carbon nanotubes, due to high conductivity, stability, and large specific surface area, have a potential ability to promote...     

Fabrication of an iron(III) PVC-membrane sensor based on bis-benzilthiocarbohydrazide as a selective sensing material

The construction, performance characteristics, and application of a novel iron(III) membrane sensor based on a new bis-benzilthiocarbohydrazide (BBTC) are reported in this paper. The sensor is prepared by incorporating of BBTC, nitrobenzene (NB), and sodium tetraphenyl borate (NaTPB) into a plasticized poly(vinyl chloride) membrane. The electrode reveals a Nernstian behavior over a wide iron ion concentration range (1.0 × 10^? 2–1.0 × 10^? 7 mol L^? 1), and relatively low detection limit (8.6 × 10^? 8 mol L^? 1). The potentiometric response is independent on the pH of the solution in the range of 1.6–4.3. The electrode shows a very short response time (< 10 s). The proposed electrode can be used for at least nine weeks without any considerable divergence in potentials. It exhibits very good selectivity relative to a wide variety of alkali, alkaline earth, transition and heavy metal ions. In fact, the selectivity of the proposed sensor shows great improvements compared to the previously reported electrodes for the iron ion. Also, the sensors accuracy was investigated in two ways: (i) with the potentiometric titration of a Fe(III) solution with EDTA and (ii) with the Fe(III) monitoring in river and wastewater samples.     

Gadolinium(III) ion selective sensor using a new synthesized Schiff's base as a sensing material

According to a solution study which showed a selective complexation between N,N′-bis(methylsalicylidene)-2-aminobenzylamine (MSAB) and gadolinium ions, MSAB was used as a sensing element in construction of a gadolinium(III) ion selective electrode. Acetophenon (AP) was used as solvent mediator and sodium tetraphenyl borate (NaTPB) as an anion excluder. The electrode showed a good selectivity towards Gd(III) ions over a wide variety of cations tested. The constructed sensor displayed a Nernstian behavior (19.7 ± 0.3 mV/decade) in the concentration range of 1.0 × 10^? 6 to 1.0 × 10^? 2 mol L^? 1 with detection limit of 5.0 × 10^? 7 mol L^? 1 and a short response time (< 10 s). The working pH range of the electrode was 3.5–10.1 and lifetime of the sensor was at least 10 weeks. Analysis of certified reference materials confirmed the accuracy of the proposed sensor. The electrode was successfully applied as an indicator electrode in gadolinium titration with EDTA.     

Recovery of EDTA from complex solution using Cu(II) as precipitant and Cu(II) subsequent removal by electrolysis

Ethylendiaminetetraacetate (EDTA) is a chelating agent widely used in industry and agriculture. Resistant to chemical and biological degradation EDTA represents a serious ecological problem. In order to avoid the outlet into the environment a new method of EDTA recycling has been proposed. The method involves substituting of the metal ions in EDTA complexes by Cu(II) and formation of an insoluble Cu2EDTA.4H2O compound at the excess of Cu(II) ions in weakly acidic solutions. Cu(II) ions substitute such metal ions as Ni(II), Zn(II), Co(II), Cd(II), Ca(II) and Mg(II). After treatment of the precipitate with water only, acidic or alkaline solutions the copper from the suspension formed can be removed by electrolysis. The highest current efficiency under galvanostatic conditions is in alkaline solutions, however, the highest yield of EDTA recovery is in acidic solutions. FT-IR investigations and chemical analysis of the precipitate formed have shown that in acidic and in alkaline solutions, H4EDTA and Na2H2EDTA.2H2O were formed, respectively. Electrolysis in acidic solutions gives the best results, i.e. the formed H4EDTA contains the highest amount of EDTA (95%) and the lowest amount of copper (0.01%).     

Tartrazine modified activated carbon for the removal of Pb(II), Cd(II) and Cr(III)

A two in one attempt for the removal of tartrazine and metal ions on activated carbon has been developed. The method was based on the modification of activated carbon with tartrazine then its application for the removal of Pb(II), Cd(II) and Cr(III) ions at different pH values. Tartrazine adsorption data were modelled using both Langmuir and Freundlich classical adsorption isotherms. The adsorption capacities qm were 121.3, 67 and 56.7mgg(-1) at initial pH values of 1.0, 6.0 and 10, respectively. The adsorption of tartrazine onto activated carbon followed second-order kinetic model. The equilibrium time was found to be 240min at pH 1.0 and 120min at pH 10 for 500mgL(-1) tartrazine concentration. A maximum removal of 85% was obtained after 1h of contact time. The presence of tartrazine as modifier enhances attractive electrostatic interactions between metal ions and carbon surface. The adsorption capacity for Pb(II), Cd(II) and Cr(III) ions has been improved with respect to non-modified carbon reaching a maximum of 140%. The adsorption capacity was found to be a pH dependent for both modified and non-modified carbon with a greater adsorption at higher pH values except for Cr(III). The enhancement percent of Pb(II), Cd(II) and Cr(III) at different pH values was varied from 28% to 140% with respect to non-modified carbon. The amount of metal ions adsorbed using static regime was 11-40% higher than that with dynamic mode. The difference between adsorption capacities could be attributed to the applied flow rate.