An infrared study on the chemisorption of tertiary phosphines on coinage and platinum group metal surfaces

The chemisorption of dimethylphenyl-, methyldiphenyl- and triphenylphosphine on evaporated gold, silver, copper, rhodium, iridium, palladium, platinum and nickel surfaces has been studied by means of infrared reflection–absorption spectroscopy (IRAS). Multilayers of physisorbed phosphine are formed on the surfaces of all metals studied except nickel after deposition from dilute toluene solution. The deposition rate varies for different metal surfaces and it is sometimes quite slow. The standard immersion time was 20 h in this study to secure that an equilibrium between the surface and the solution is reached. Several minutes of ultrasonic treatment are required to get rid of the physisorbed phosphine, leaving a very thin layer of chemisorbed phosphine on the metal surface. Most of the absorption bands in IRAS spectra of these thin layers show significant shifts, which are especially large for dimethylphenylphosphine. It is evident that the electron distribution in the entire phosphine molecules is changed and that the chemisorption to the coinage and platinum group metal surfaces is strong. Infrared spectra of coordination compounds of gold(I), silver(I) and copper(I) with dimethylphenyl-, methyldiphenyl- and triphenylphosphine and of the corresponding phosphine oxides have served as reference material for the chemisorbed phosphines. The spectra of the coordination compounds show similar shifts and intensity changes as the IRAS spectra of tertiary phosphines chemisorbed on the coinage and platinum group metals. This suggests that the studied phosphines are as strongly bound to the coinage and platinum group metal surfaces as to the monovalent coinage metal ions known to form very stable complexes with tertiary phosphines.     

Chemically bonded multiwalled carbon nanotubes as efficient material for solid phase extraction of some metal ions in food samples

Multiwalled carbon nanotubes chemically functionalized with 2-((3-silylpropylimino) methyl) phenol (SPIMP-MWCNT) and successfully applied for the solid phase extraction (SPE) of some metal ions in food samples. The influences of the analytical parameters including pH, amounts of solid phase, eluent conditions (type, volume and concentrations), sample volume and interference of some metal ions on the recoveries of ions Cu²⁺, Pb²⁺, Fe²⁺, Ni²⁺ and Zn²⁺ ion were investigated. The metal ions retained on SPIMP-MWCNT was eluted using 6?mL of 4?mol?L^?1 HNO₃ solution and their content was determined by flame atomic absorption spectrometry (FAAS) with recoveries more than 95% and relative standard deviations (n?=?5) between 2.4–3.4% for both reproducibility and repeatability. The detection limit of this metal ions was between 1.0–2.6?ng?mL^?1 (3S _b , n?=?10) and their preconcentration factor was 100, while their loading capacity was above 32.9?mg?g^?1 of SPIMP-MWCNT. The proposed method was successfully applied for the preconcentration and determination of analytes in different samples.     

A survey of crystal structures and biological activities of platinum group metal complexes containing N-acylthiourea ligands

Abstract

N-Acyl-thioureas are important compounds in the field of organic synthesis and medicinal chemistry. Research interest in these compounds has grown recently because coordination to metal ions enhances their application especially in view of medicinal studies. These thiourea derivatives possess rich coordination chemistry and the coordination behavior of these derivatives alters upon reaction with different metals. Such ligands generally coordinate to Pt(II) and Pd(II) ions in a bidentate S,O manner and often coordinate to Ru(II), Rh(III) and Ir(III) centers through the S donor atom. We isolated some complexes of these ligands by reaction with sodium azide which coordinates to Ru(II), Rh(III), and Ir(III) in a bidentate S,N fashion. The deprotonated thiourea nitrogen atom resulted in the formation of strained 4-membered ring structures around the metal center. Biological application of N-acyl thiourea derivatives and their platinum group metal complexes are further discussed. Studies has shown that these compounds can be used as drugs to treat several human diseases like microbial infections, tuberculosis, carcinomas, malaria, leishmaniasis, urease inhibitors and anti-inflammatory. This review intends to summarize the recent advancement in the chemistry of N-acyl-thioureas and highlight some perspectives in the synthesis, versatile coordination behavior to ruthenium, rhodium, iridium, platinum and palladium, and their metal complexes in biological applications.     

Transport and separation of Ag(+) and Zn(2+) by donnan dialysis through a monovalent cation selective membrane

Donnan Dialysis of Ag⁺ and Zn²⁺ was investigated through a cation exchange membrane (CMS Neosepta) when a proton concentration difference was maintained between the two sides of the membrane. Developed for the production of brine from sea water, CMS Neosepta showed a higher permeability to monovalent than to bivalent cations. Several physico-chemical parameters have been determined (electrical resistance, membrane potential, sorption of electrolytes, Zn²⁺ and Ag⁺ diffusion coefficients). The flux of Ag⁺ and the diffusion potential in the membrane increase with HNO₃ concentrations. Ag⁺ and Zn²⁺ can be separated because of the preferential membrane transfer for Ag⁺.     

Determination of cadmium by flame atomic absorption spectrometry after preconcentration on naphthalene-methyltrioctylammonium chloride adsorbent as tetraiodocadmate (II) ions

A sensitive and simple solid-phase preconcentration procedure for enrichment of cadmium prior to analysis by flame atomic absorption spectrometry (FAAS) is described. The method is based on the adsorption of cadmium as CdI₄²⁻ on naphthalene-methyltrioctylammonium chloride adsorbent, elution by nitric acid and subsequent determination by FAAS. The effect of pH, iodide concentration, sample flow rate, volume of the sample and diverse ions on the recovery of the analyte was investigated and optimum conditions were established. A preconcentration factor of 40 was achieved using the optimum conditions. The calibration graph was linear in the range 1-100 ng ml⁻¹ cadmium in the initial solution. The detection limit based on the 3S_b criterion was 0.6 ng ml⁻¹ and the relative standard deviations (RSD) were 3.9 and 1.05% for 5 and 40 ng ml⁻¹, respectively (n=8). The method was successfully applied to the determination of cadmium added to river, tap and Persian Gulf water samples.     

Chemically-modified activated carbon with ethylenediamine for selective solid-phase extraction and preconcentration of metal ions

A new method that utilizes ethylenediamine-modified activated carbon (AC-EDA) as a solid-phase extractant has been developed for simultaneous preconcentration of trace Cr(III), Fe(III), Hg(II) and Pb(II) prior to the measurement by inductively coupled plasma optical emission spectrometry (ICP-OES). The new sorbent was prepared by oxidative surface modification. Experimental conditions for effective adsorption of trace levels of Cr(III), Fe(III), Hg(II) and Pb(II) were optimized with respect to different experimental parameters using batch and column procedures in detail. The optimum pH value for the separation of metal ions simultaneously on the new sorbent was 4.0. Complete elution of absorbed metal ions from the sorbent surface was carried out using 3.0 mL of 2% (%w/w) thiourea and 0.5 mol L⁻¹ HCl solution. Common coexisting ions did not interfere with the separation and determination of target metal ions. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 39.4, 28.9, 60.5 and 49.9 mg g⁻¹ for Cr(III), Fe(III), Hg(II) and Pb(II), respectively. The time for 94% adsorption of target metal ions was less than 2 min. The detection limits of the method was found to be 0.28, 0.22, 0.09 and 0.17 ng mL⁻¹ for Cr(III), Fe(III), Hg(II) and Pb(II), respectively. The precision (R.S.D.) of the method was lower 4.0% (n = 8). The prepared sorbent as solid-phase extractant was successfully applied for the preconcentration of trace Cr(III), Fe(III), Hg(II) and Pb(II) in natural and certified samples with satisfactory results.     

Solid-phase extraction using multiwalled carbon nanotubes and quinalizarin for preconcentration and determination of trace amounts of some heavy metals in food,water and environmental samples

A solid phase extraction procedure has been developed using multiwalled carbon nanotubes (MWCNTs) as a solid sorbent and quinalizarin [1,2,5,8-tetrahydroxyanthracene-9,10-dione] as a chelating agent for separation and preconcentration of trace amounts of some heavy metal ions, Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II) before their determination by flame atomic absorption spectroscopy (FAAS). The influences of the analytical parameters, including pH, amounts of quinalizarin and adsorbent, sample volume, elution conditions such as volume and concentration of eluent, flow rates of solution and matrix ions, were investigated for the optimum recoveries of the analyte ions. No interference effects were observed from the foreign metal ions. The preconcentration factor was 100. The detection limit (LOD) for the investigated metals at the optimal conditions were observed in the range of 0.30–0.65 μg L^?1. The relative standard deviation (RSDs), and the recoveries of standard addition for this method were lower than 5.0% and 96–102%, respectively. The new procedure was successfully applied to the determination of analytes in food, water and environmental samples with satisfactory results.     

1-(2-Formamidoethyl)-3-phenylurea functionalized activated carbon for selective solid-phase extraction and preconcentration of metal ions

A novel method that utilizes 1-(2-formamidoethyl)-3-phenylurea-modified activated carbon (AC-1-(2-formamidoethyl)-3-phenylurea) as a solid-phase extractant has been developed for simultaneous preconcentration of trace Cr(III), Cu(II), Fe(III) and Pb(II) prior to the measurement by inductively coupled plasma atomic emission spectrometry (ICP-AES). Experimental conditions for effective adsorption of trace levels of Cr(III), Cu(II), Fe(III) and Pb(II) were optimized using batch and column procedures in detail. The optimum pH value for the separation of metal ions simultaneously on the new sorbent was 4. And the adsorbed metal ions could be completely eluted by using 2.0 mL 2.0 mol L⁻¹ HCl solution. Common coexisting ions did not interfere with the separation and determination of target metal ions. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 39.8, 39.9, 77.8 and 17.3 mg g⁻¹ for Cr(III), Cu(II), Fe(III) and Pb(II), respectively. The detection limits of the method were found to be 0.15, 0.41, 0.27 and 0.36 ng mL⁻¹ for Cr(III), Cu(II), Fe(III) and Pb(II), respectively. The relative standard deviation (RSD) of the method was lower than 4.0% (n = 8). The method was successfully applied for the preconcentration of trace Cr(III), Cu(II), Fe(III) and Pb(II) in natural and certified samples with satisfactory results.     

Application of Doehlert designs for optimisation of an on-line preconcentration system for copper determination by flame atomic absorption spectrometry

In the present paper, a system for on-line preconcentration and determination of copper by flame atomic absorption spectrometry (FAAS) was developed. It was based on solid phase extraction of copper(II) ions on a minicolumn of Amberlite XAD-2 loaded with 2-(2-thiazolylazo)-5-dimethylaminophenol (TAM). The optimisation process was carried out using Doehlert designs. Four variables (sampling flow rate, SR; elution flow rate, buffer concentration, BC; and pH) were regarded as factors in the optimisation. The parameter “sensitivity efficiency (SE)” proposed in this paper, and defined as the analytical signal obtained for an on-line enrichment system for a preconcentration time of 1 min was used as analytical response in the optimisation process. Using the established experimental conditions, the proposed on-line system allowed determination of copper with detection limit (3σ/S) of 0.23 μg l⁻¹, and a precision (repeatability), calculated as relative standard deviation (R.S.D.) of 3.9 and 3.7% for copper concentration of 5.00 and 20.00 μg l⁻¹, respectively. The preconcentration factor obtained is 62. The recovery achieved for copper determination in presence of several cations demonstrated that this has enough selectivity for analysis of food samples. The robustness of the proposed system was also evaluated. The accuracy was confirmed by analysis of the following certified reference materials (CRMs): Rice flour NIES 10a, Spinach leaves NIST 1570a, Apples leaves NIST 1515 and Orchard leaves NBS 1571. This procedure was applied for copper determination in natural food samples.     

Optical metal-organic framework sensor for selective discrimination of some toxic metal ions in water

This paper reports the development of a facile and effective approach, based on the use of Zr-based metal-organic frameworks (UiO-66) sensor with micropores geometry, shape and particle morphology for the visual detection and removal of ultra-traces of some toxic metal ions such as Bi(III), Zn(II), Pb(II), Hg(II) and Cd(II). UiO-66 was used as selective carriers for accommodating hydrophobic chromophore probes such as dithizone (DZ) without coupling agent for sensitive and selective discrimination of trace level of toxic analytes. The developed UiO-66 sensor was utilized for the detection of ultra-traces of some toxic metal ions with the naked eye. The new sensor displays high sensitivity and selectivity of a wide range of detectable metals analytes up to 10⁻¹⁰ mol dm⁻³ in solution, in a rapid analyte uptake response (seconds). The developed sensor is stable, cost effective, easy to prepare, and would be useful for rapid detection and removal of ultra-traces of toxic metal ions in water samples.     

Primary reactions in the photochemistry of hexahalide complexes of platinum group metals: A minireview

We review the results obtained for Pt^IVCl₆²⁻, Pt^IVBr₆²⁻, Ir^IVCl₆²⁻, Ir^IVBr₆²⁻, and Os^IVBr₆²⁻ complexes in aqueous and alcoholic solutions using ultrafast pump–probe spectroscopy, laser flash photolysis, ESR, and photoelectron spectroscopy. We discuss the correlations between the photophysics and the photochemistry of these complexes. The key reaction for Pt^IVCl₆²⁻ is the inner-sphere electron transfer, which results in an Adamson radical pair that lives for several picoseconds, and the subsequent photoaquation in aqueous solutions and photoreduction in alcohols. The chlorine atom formed as the primary product escapes the solvent cage in aqueous solutions or oxidizes a solvent alcohol molecule via secondary electron transfer, producing secondary intermediates that react on the microsecond time scale. The photoexcitation of Pt^IVBr₆²⁻ results in the formation of pentacoordinated Pt^IV intermediates, i.e. ³Pt^IVBr₅⁻ and ¹Pt^IVBr₅⁻, with characteristic lifetimes of approximately 1 and 10 ps, respectively. Subsequent reactions of these intermediates result in the complexation of a solvent molecule. Photoreduction is also possible in alcohols. Similar reactions occur with rather low quantum yields for Ir^IVCl₆²⁻, therefore, only the ground-state recovery could be monitored in ultrafast experiments, which occur on the 10-ps time scale. The photochemical behaviours of the Ir^IVBr₆²⁻ and Os^IVBr₆²⁻ complexes are similar to those of Ir^IVCl₆²⁻ and Pt^IVBr₆²⁻, respectively.     

Determination of trace metal ions via on-line separation and preconcentration by means of chelating Sepharose beads in a sequential injection lab-on-valve (SI-LOV) system coupled to electrothermal atomic absorption spectrometric detection

The analytical performance of an on-line sequential injection lab-on-valve (SI-LOV) system using chelating Sepharose beads as sorbent material for the determination of ultra-trace levels of Cd(II), Pb(II) and Ni(II) by electrothermal atomic absorption spectrometry (ETAAS) is described and discussed. The samples are adjusted to pH 5.0 on-line in the system for optimum operation. The target ions are adsorbed by chelation on the surface of the beads, contained in a 20 μl microcolumn within the LOV, and following elution by 50 μl 2 M nitric acid, the eluate is, as sandwiched by air segments, introduced into the ETAAS. Based on the consumption of 1.8 ml sample solution, retention efficiencies of 95, 75 and 90%, enrichment factors of 34, 27 and 32, and determination limits of 0.001, 0.07 and 0.02 μg l⁻¹ were obtained for Cd(II), Pb(II) and Ni(II), respectively. The beads can be used repeatedly for at least 20 times without decrease of performance, yet can be replaced at will if the circumstances should so dictate. The optimized procedural parameters showed that 12 samples per hour could be prepared and successfully analyzed. The results obtained for three standard reference materials agreed very well with the certified values.     

Solvent impregnated hollow fibre for a selective preconcentration of Pb(II) in an on-line determination by flame atomic absorption spectrometry

A solvent impregnated hollow fibre (SIHF) module has been developed for the preconcentration of lead by using bis(2-ethylhexyl) phosphoric acid (DEHPA) dissolved in kerosene as extractant. The module has been designed for an on-line determination of trace amounts of lead(II) at mg l⁻¹ (ppm) level by flame atomic absorption spectrometry (FAAS).

The SIHF system is based on the metal liquid–liquid distribution between aqueous solutions of different acidity and the mentioned organic solution. The highest enrichment factor of Pb(II) was determined at pH=4.0 using a formic acid/formiate buffer solution.

Preconcentration experiments were carried out at low lead(II) concentration (mg l⁻¹ level) by using the SIHF module. This study includes the influence of hydrodynamic and chemical conditions on the loading and elution of Pb(II) on the SIHF, i.e., flow rate through the fibres, acidity of the eluent (as nitric acid concentration) and the chemical nature of the acid used in the elution. Breakthrough curves were determined for different sampling flow rates, 0.54 ml min⁻¹ was selected to minimise the loading volume of Pb(II) sample. 0.1 M nitric acid was chosen as eluent solution, and perchloric acid also shows appropriate elution characteristics. The degree of concentration obtained for Pb(II) are of 10 fold the original concentration. The quantification limit for Pb(II) achieved with this preconcentration system is 0.17 mg l⁻¹.

The results obtained indicate that the SIHF system can be applied for on-line determination of trace amounts of lead(II) by FAAS.     

Application of full factorial design for the preconcentration of chromium by solid phase extraction with Amberlyst 36 resin

The preconcentration of chromium(III) by solid phase extraction and its determination from aqueous solutions by flame atomic absorption spectrometry (FAAS) is investigated by applying an experimental design. The optimization of the preconcentration variables such as pH of the sample solution, flow rate of the sample solution and concentration of elution solution was carried out using 2³ full factorial design. The most important parameter affecting the preconcentration of chromium is the concentration of eluent. In the established experimental conditions, chromium can be determined with a relative standard deviation of 2.0% (N = 7) for a chromium concentration of 100 μg L⁻¹. The detection limit for chromium was 1 μg L⁻¹ (N = 20). The adsorption capacity of Amberlyst 36 is found to be 90.9 mg g⁻¹ for chromium. Effect of other ions on the procedure was also evaluated. The method was validated by the analysis of certified reference materials (tea leaves GBW 07605 and fish tissue IAEA-407). The method was applied to the determination of chromium in waste water, dam water, carrot, parsley and lettuce. Correspondence: Ali Rehber Türker, Department of Chemistry, Faculty of Science and Arts, Gazi University, TR-06500 Ankara, Turkey     

Solid phase selective separation and preconcentration of Cu(II) by Cu(II)-imprinted polymethacrylic microbeads

Ion-imprinted polymer (IIP) particles are prepared by copolymerization of methacrylic acid as monomer, trimethylolpropane trimethacrylate as crosslinking agent and 2,2′-azo-bis-isobutyronitrile as initiator in the presence of Cu(II), a Cu(II)-4-(2-pyridylazo)resorcinol (Cu(II)-PAR) complex, and PAR only. A batch procedure is used for the determination of the characteristics of the Cu(II) solid phase extraction from the IIP produced. The results obtained show that the Cu(II)-PAR IIP has the greatest adsorption capacity (37.4 μmol g⁻¹ of dry copolymer) among the IIPs investigated. The optimal pH value for the quantitative preconcentration is 7, and full desorption is achieved by 1 M HNO₃. The selectivity coefficients (S_Cu/Me) for Me = Ni(II), Co(II) are 45.0 and 38.5, respectively. It is established that Cu(II)-PAR IIPs can be used repeatedly without a considerable adsorption capacity loss. The determination of Cu(II) ions in seawater shows that the interfering matrix does not influence the preconcentration and selectivity values of the Cu(II)-PAR IIPs. The detection and quantification limits are 0.001 μmol L⁻¹ (3σ) and 0.003 μmol L⁻¹ (6σ), respectively.     

Use of 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel for automated preconcentration and selective determination of antimony(III) by flow-injection electrothermal atomic absorption spectrometry

Selective sorption of Sb(III) on a microcolumn packed with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel (DPTH-gel) has been used for determination of Sb(III). A flow-injection system comprising a microcolumn connected to the tip of the autosampler was used for preconcentration. The sorbed antimony was eluted with nitric acid directly into the graphite furnace and determined by AAS. The detection limit for antimony under the optimum conditions was 0.3 ng mL^–1. This procedure was used for determination of antimony in natural water, soil, vegetation, and a certified sample of a city waste incineration ash (BCR 176).     

Acid extraction and cloud point preconcentration as sample preparation strategies for cobalt determination in biological materials by thermospray flame furnace atomic absorption spectrometry

A thermospray flame furnace atomic absorption spectrometer (TS-FF-AAS) was employed for Co determination in biological materials. Cobalt presents a high atomization temperature and consequently poor sensitivity is obtained without changing its thermochemical behavior. The effect of different complexing agents on sensitivity was evaluated based on the formation of Co volatile compounds. A cloud point procedure was optimized for Co preconcentration for further improvement of sensitivity. Samples were treated with 1 mol l^− 1 hydrochloric acid solution for quantitative extraction of Co without simultaneous extraction of Fe, since it is a strong interferent. After the extraction and preconcentration steps, a sample volume of 150 μl was introduced into the hot Ni tube using air as carrier at a flow-rate of 0.4 ml min^− 1. The best sensitivity was attained using ammonium pyrrolidinedithiocarbamate (APDC) and Triton X-114 was employed for implementation of the cloud point procedure. The detection limit obtained for Co was 2.1 μg l^− 1 and the standard deviation was 5.8% for a solution containing 100 μg l^− 1 (n = 10). Accuracy was checked using two certified reference materials (tomato leaves and bovine liver) and results were in agreement with certified values at a 95% confidence level. Employing the developed procedure, Co were quantified in different biological materials (plant and animal tissues). The proposed method presents suitable sensitivity for cobalt determination in the quality control of foods.     

石墨炉原子吸收光谱测硼时基体改进剂的选择

研究各种基体改进剂的增感效果,和它们对灰化、原子化温度的影响。结果表明,Ca、Sr、Ca-Mg、Ca-La、Sr-Mg均可作为硼的基体改进剂,且Ca-Mg、Ca-La、Sr-Mg较之Ca、Sr性能优越。并分别以Ca、Ca-Mg、Sr-Mg作基体改进剂,直接分析饮用水中痕量硼,所得结果基本一致,相对标准偏差均在10%以内。     

Determination of trace elements in seawater by electrothermal atomic absorption spectrometry with and without a preconcentration step

The determination of the trace metals Cd, Pb and Cu in seawater by electrothermal atomic absorption spectrometry (ETA-AAS) has been investigated. A combination of the platform with mixed palladium nitrate-magnesium nitrate as matrix modifier and Zeeman background correction allows Cd an Pb to be determined by aqueous standard calibration in appropriately diluted seawater samples. Copper can be determined in undiluted seawater samples without chemical modification using a standard additions method. Detection limits (3) of 2.97,5.27 and 1.1 gl^–1 are obtained for Cd, Pb and Cu respectively. A Kelex-100 impregnated silica C18 material (Kelex 100-C18) has been tried and has proved to be effective as a column packing for extraction/preconcentration of these metals from seawater. Using the column extraction method, the sensitivity of the graphite furnace technique is enhanced 50-fold using a 10 l injection volume. Thus, the determination of the studied three metals in seawater at the ng.l^–1 level could be achieved.     

Simplified cloud point extraction for the preconcentration of ultra-trace amounts of gold prior to determination by electrothermal atomic absorption spectrometry

A simple and sensitive cloud point extraction method has been developed for the preconcentration of ultra-trace amounts of gold as a prior step to its determination by electrothermal atomic absorption spectrometry. It is based on the extraction of gold in hydrochloric acid medium using the non-ionic surfactant polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5) without adding a chelating agent. The preconcentration of a 50 mL sample solution was thus enhanced by a factor of 200. The resulting calibration graph was linear in the range of 10–200 ng L⁻¹ with a correlation coefficient of 0.9993. The limit of detection (3s) obtained under optimal conditions was 2.0 ng L⁻¹. The relative standard deviation for 10 replicate determinations at a 100 ng L⁻¹ Au level was 3.6%. The method was applied to the ultra-trace determination of gold in water and copper samples.