Sorption and preconcentration of metal ions in ethanol solution with a silica gel surface chemically modified with benzimidazole

The adsorption isotherms of MCl(2) (M Mn, Ni, Cu, Zn and Cd) and FeCl(3) by silica gel chemically modified with benzimidazole molecules ( Si(CH(2))(3)NC(7)H(5)N) were studied in ethanol solution at 298 K. A column made of modified silica was used to adsorb and preconcentrate the above metal ions from ethanol solution. Elution was done with 0.1 M hydrochloric acid in an ethanol/water mixture having a mole fraction of water of 0.8. The material was applied in the preconcentration of metal ions from commercial ethanol normally used as engine fuel.     

Characterization and application of silylated substrates for the preconcentration of cations

Chelating functional groups immobilized on silica and controlled pore glass beads are used to preconcentrate cations from aqueous solution in the concentration region of ng ml^?1. The functional groups are chemically bonded to the substrates by silylation reagents which may be employed as received or further modified. For example, commercially available 1,2-diamines may be used or converted to the dithiocarbamate after immobilization. This report includes studies of ionic strength and sodium chloride effects on the recovery of transition metal ions. Batch extraction of transition metal ions is accomplished with silica as the substrate for solutions containing transition metal ions at μg ml^?1 concentrations. Column extraction of solutions pumped at 50 ml min^?1 is accomplished at concentrations of 25 ng ml^?1. Recovery is good in both cases. The cations were determined directly on pelletized substrates by x-ray fluorescence. However, the ions may be eluted from the substrate and determined by other methods. Examples of determinations of several cations in lake water and high-purity industrial water are given.     

Chemically modified silica gel for selective solid-phase extraction and preconcentration of heavy metal ions

This paper describes our research on the synthesis of the sorbent with chemically bonded ketoimine groups, and, furthermore, using this sorbent in the SPE technique to extract and preconcentrate trace amounts of metal ions in water samples. Surface characteristics of the sorbent were determined by elemental analysis, NMR spectra for the solid phases (²⁹Si CP MAS NMR), and analysis of pore size distribution of the sorbent and nitrogen adsorption-desorption. The newly proposed sorbent with ketoimine groups was applied for the extraction and preconcentration of trace amounts of Cu (II), Cr (III) and Zn (II) ions from the water from a lake, post-industrial water and purified water unburdened back to the lake. The determination of the transition-metal ions was performed on an emission spectroscope with inductively coupled plasma ICP-OES. For the batch method, the optimum pH range for Cu (II) and Cr (III) extraction was equal to 5, and Zn(II)–to 8. All the metal ions can be desorbed from SPE columns with 10?mL of 0.5?mol?HNO₃. The detection limits of the method were found to be 0.7?µg?L^?1 for Cu (II), 0.08?µg?L^?1 for Cr (III), and 0.2?µg?L^?1 for Zn (II), respectively.     

Quinalizarin anchored on Amberlite XAD-2. A new matrix for solid-phase extraction of metal ions for flame atomic absorption spectrometric determination

Amberlite XAD-2 has been functionalized by coupling it to quinalizarin [1,2,5,8-tetrahydroxyanthraquinone] by means of an -N = N- spacer. Elemental analysis, thermogravimetric analysis, and infrared spectra were used to characterize the resulting new polymer matrix. The matrix has been used to preconcentrate Cu(II), Cd(II), Co(II), Pb(II), Zn(II), and Mn(II) before their determination by flame atomic absorption spectrometry (FAAS). UO₂(II) has been preconcentrated for fluorimetric determination. The optimum pH values for maximum adsorption of the metals are between 5.0 and 7.0. All these metal ions are desorbed (recovery 91–99%) with 4 mol L^–1 HNO₃. The adsorptive capacity of the resin was found to be in the range 0.94–5.28 mg metal g^–1 resin and loading half-life (t_1/2) between 5.3 and 15.0 min. The effects of NaF, NaCl, NaNO₃, Na₂SO₄, Na₃PO₄, Ca(II), and Mg(II) on the adsorption of these metal ions (0.2 μg mL^–1) are reported. The lower limits of detection for these metal ions are between 1 and 15.0 μg L^–1. After enrichment on this matrix flame AAS has been used to determine these metal ions (except the uranyl ion) in river water samples (RSD ≤ 6.5%); fluorimetry was used to determine uranyl ion in well water samples (RSD ≤ 6.3%). Cobalt from pharmaceutical vitamin tablets was preconcentrated by use of this chelating resin and estimated by FAAS (RSD ～ 4%).     

A column system for the selective extraction of U(VI) and Th(IV) using a new chelating sorbent

A new method has been developed using (bis-3,4-dihydroxy benzyl)p-phenylene diamine functionalized to XAD-16 (a polystyrene divinyl benzene copolymer) matrix, to preconcentrate mainly U(VI) and Th(IV) from synthetic and real samples. The developed method is free from matrix interference due to alkali and alkaline metal ions and preconcentrates the actinides with a high degree of selectivity, with consistent trace recoveries. The new chelating resin provides dramatic improvement in metal exchange rate, with half value saturation time (t_1/2) of less than 1.6 min. The developed method was superior in its metal loading capacity for U(VI) and Th(IV), with values of 0.666 and 0.664 mmol g⁻¹, respectively. Various physio-chemical properties like effect of solution pH, kinetic studies, resin loading capacity, sample breakthrough volume, matrix effects etc., on metal ion sorption to sorbent phase, were studied using both batch and column method. The new chelatogen was applied to extract U(VI) from near neutral real water samples. Preconcentration and separation of metal ions were possible through pH variation and also by varying the eluant concentration. A high preconcentration factor value of 350 with a lower limit of detection of 20 and 30 ng cm⁻³ was obtained for U(VI) and Th(IV), respectively. The practical applicability of the developed resin was examined using synthetic and real samples such as sea/well water samples. The method provides low relative standard deviation values of <3.5% for all analytical measurements, reflecting on the reproducibility and accuracy of the developed method. The new resin is quite durable with recycling time >35 cycles, without any major change in its quantitative metal uptake nature.     

Luminescence Method for Studying the Formation and Stability of Macromolecular Complexes of Transition Metals with Carboxyl-Containing Polymers in Organic Solvents

Quenching of the luminescence of carboxyl-containing polymer molecules containing a luminescent marker by transition metal ions (Cu²⁺, Ni²⁺) is observed not only in aqueous and aqueous-salt solutions, but also in polar organic solvents (methanol, ethanol, dimethylformamide). In dilute solutions, quenching refl ects binding of metal ions with the polymer and changes in the degree of filling of the polymer carboxyl groups with transition metal ions quenching the luminescence. The equilibrium stability constant of the formed macromolecular metal complex in organic media can be quantitatively estimated from the quenching effect using the relationships that follow from the law of mass action. The formation and stability of Cu²⁺ and Ni²⁺ complexes with polymethacrylic acid in protic (methanol, ethanol) and aprotic (dimethylformamide) solvents at low polymer concentrations (0.4–0.02 mg mL^–1) were studied using the quenching effect. In methanol, in contrast to ethanol and dimethylformamide, two mechanisms of binding of transition metal ions with different equilibrium stability constants of the complexes (\({K_{{1^{st}}}}\) > 3 × 10⁹ and \({K_{{2^{st}}}}\) ≈ 10⁶–10⁴) were revealed. The infl uence exerted on the stability of the complexes and on the complexation mechanism by the nature and acidity of the organic solvent, polymer concentration, kind of the transition metal ion quenching the luminescence, and NaOH and HCl additions was studied. The results obtained demonstrate the efficiency of the luminescence method used and prospects for its further use for studying polymer systems containing transition metal ions in organic solvents.     

Vortex-assisted magnetic solid phase extraction of Cd(II), Cu(II) and Pb(II) on the Nitroso–R salt impregnated magnetic Ambersorb 563 for their separation,preconcentration and determination by FAAS

A novel vortex-assisted magnetic solid phase extraction method followed by flame atomic absorption spectrometry was improved to separate, preconcentrate and determine the lead, copper and cadmium ions by using 1-Nitro-2-naphthol-3, 6-disulfonic acid disodium salt (Nitroso-R salt) impregnated magnetic Ambersorb-563 resin. The adsorbent was characterised by Fourier transform infrared spectra, BET surface analyser and scanning electron microscopy. The influences of various analytical parameters, such as pH value, type and volume of the eluent, sample volume, were optimised and the effects of potentially interfering ions were investigated. The analyte ions were quantitatively recovered at pH 7.0 on magnetic adsorbent and desorbed with a 2.0 M HNO₃ in 10% acetone as eluent. The detection limits were 1.4, 5.8 and 1.5 ng mL^?1 for Cd(II), Cu(II) and Pb(II), respectively. The method has been validated with analytically by the analysis certified reference materials and standard additions prior to application to determine metal ions in water samples.     

On-line sorption preconcentration of metals based on mixed micelle cloud point extraction prior to their determination with micellar chemiluminescence: Application to the determination of chromium at ng l levels

The on-line incorporation of cloud point extraction (CPE) to flow injection analysis (FIA) is modified to extract and preconcentrate metal species rapidly, avoiding the formation of hydrophobic complexes, using a mixed micellar medium. Coupling the procedure with chemiluminescence (CL) detection based on the catalytic activity of metal species on the luminol-hydrogen peroxide reaction and enhancing the signal with the presence of a micellar carrier containing bromide ions produces a powerful tool for the preconcentration and determination of metal species at ng l⁻¹ levels. As an analytical demonstration ultratrace concentrations of chromium were conveniently detected and quantified in samples with a complex matrix such as seawater and wastewater. The figures of merit for the determination of chromium were: 0.9-1.6% R.S.D. (n=5) with detection and quantification limits 0.5 and 2.0 ng l⁻¹, respectively. The calibration graph was rectilinear from 2 to 200 ng l⁻¹ (r=0.9996, n=6). Several other metal ions were determined in ideal situations, with analogous results.     

Galvanic Replacement Reactions of Active‐Metal Nanoparticles

We present a systemic investigation of a galvanic replacement technique in which active‐metal nanoparticles are used as sacrificial seeds. We found that different nanostructures can be controllably synthesized by varying the type of more noble‐metal ions and liquid medium. Specifically, nano‐heterostructures of noble metal (Ag, Au) or Cu nanocrystals on active‐metal (Mg, Zn) cores were obtained by the reaction of active‐metal nanoparticles with more noble‐metal ions in ethanol; Ag nanocrystal arrays were produced by the reaction of active‐metal nanoparticles with Ag⁺ ions in water; spongy Au nanospheres were generated by the reaction of active‐metal nanoparticles with AuCl₄^? ions in water; and SnO₂ nanoparticles were prepared when Sn²⁺ were used as the oxidant ions. The key factors determining the product morphology are shown to be the reactivity of the liquid medium and the nature of the oxidant–reductant couple, whereas Mg and Zn nanoparticles played similar roles in achieving various nanostructures. When microsized Mg and Zn particles were used as seeds in similar reactions, the products were mainly noble‐metal dendrites. The new approach proposed in this study expands the capability of the conventional nanoscale galvanic replacement method and provides new avenues to various structures, which are expected to have many potential applications in catalysis, optoelectronics, and biomedicine.     

The mechanisms of removal of heavy metals from water by ionizing radiation

The removal of heavy metal ions from water using electron beam and gamma irradiation has been investigated for the cases of Pb²⁺ and Hg²⁺ ions. These metal ions are reduced by hydrated electrons and hydrogen atoms to lower or zero valence state and eventually precipitate out of solution. Ethanol is applied as a relatively non-toxic additive to scavenge ^·OH radicals, to enhance reduction and inhibit oxidation. Mercury can be completely (>99.9%) removed from aqueous solution of 1×10⁻³ mol L⁻¹ mercury (II) chloride by using a 3 kGy dose. However, a 40 kGy dose is required to remove 96% of lead ions from a 1×10⁻³ mol L⁻¹ of PbCl₂ solution. The effect of dissolved oxygen and carbonate were also investigated. E-beam irradiation of 1×10⁻³ mol L⁻¹ lead ions complexed with ethylenediamine tetraacetic acid (EDTA) in deoxygenated as well as air-saturated solutions in the absence of ethanol resulted in removal of about 97% of the lead.     

Quinalizarin anchored on Amberlite XAD-2. A new matrix for solid-phase extraction of metal ions for flame atomic absorption spectrometric determination

Amberlite XAD-2 has been functionalized by coupling it to quinalizarin [1,2,5,8-tetrahydroxyanthraquinone] by means of an -N = N- spacer. Elemental analysis, thermogravimetric analysis, and infrared spectra were used to characterize the resulting new polymer matrix. The matrix has been used to preconcentrate Cu(II), Cd(II), Co(II), Pb(II), Zn(II), and Mn(II) before their determination by flame atomic absorption spectrometry (FAAS). UO2(II) has been preconcentrated for fluorimetric determination. The optimum pH values for maximum adsorption of the metals are between 5.0 and 7.0. All these metal ions are desorbed (recovery 91-99%) with 4 mol L(-1) HNO3. The adsorptive capacity of the resin was found to be in the range 0.94-5.28 mg metal g(-1) resin and loading half-life (t1/2) between 5.3 and 15.0 min. The effects of NaF, NaCl, NaNO3, Na2SO4, Na3PO4, Ca(II), and Mg(II) on the adsorption of these metal ions (0.2 microg mL(-1)) are reported. The lower limits of detection for these metal ions are between 1 and 15.0 microg L(-1). After enrichment on this matrix flame AAS has been used to determine these metal ions (except the uranyl ion) in river water samples (RSD < or = 6.5%); fluorimetry was used to determine uranyl ion in well water samples (RSD < or = 6.3%). Cobalt from pharmaceutical vitamin tablets was preconcentrated by use of this chelating resin and estimated by FAAS (RSD approximately 4%).     

Preconcentration of Metal Ions with Anion-Exchange Resin

A method to preconcentrate metal ions employed an anion-exchange resin was studied. Metal ions were first chelated with ethylenediaminetetraacetic acid (EDTA), then trapped on an enrichment column packed with anion-exchange resin. The major interfering ions, e.g. calcium and magnesium were excluded from enrichment by appropriate adjustment of pH. Desorption of the trapped metals was effected by elution with HCl (0.1 M). Recoveries of Cu²⁺, Ni²⁺, Co²⁺, Pb²⁺, Zn²⁺ reached 99%. By comparison with preconcentration methods using cation-exchange resin, this method has the advantages of selectivity, quantitative recovery, small cost of operation, and simple procedure.     

Spectrophotometric Determination of Trace Amounts of Titanium in Geochemical and Metallurgical Samples

Abstract

The reaction between cyclohexan-1,2-dione bissalicyloylhydrazone and titanium(IV) has been studied spectrophotometrically. An orange complex (λ = 470 nm, ? = 1.49 × 10⁴ 1.mol^?1.cm^?1) is quickly formed at pH 1–2.5 in a 3+2 V/V ethanol/water medium. Interferences (more than 65 species) have been investigated. In presence of some masking agents most of metal ions do not interfere. The orange complex has been satisfactorily used for the determination of titanium in amphibolites, granites, suspended matter, Portland cement, bauxite, cast iron and duraluminium alloy. The results are compared with those obtained using AAS and ICP methods.     

Carbazole-based Schiff base: A sensitive fluorescent ‘turn-on’ chemosensor for recognition of Al(III) ions in aqueous-alcohol media

Carbazole-based Schiff base chemosensor was synthesized in one-pot synthesis using 2-hydroxy-1-naphtaldehyde for fluorescent sensing of Al³⁺ ions. Characterization of the ligand (L) was revealed through spectroscopic and physicochemical techniques. The fluorescence emission responses of L to various metal ions and anions were investigated. The chelation was studied by UV–vis, ¹H NMR, LC-MS/MS, fluorescence titration and Job’s plot analysis. Bathochromic shift resulted from charge transfer from L to electrophilic Al³⁺ ion was observed in the chelation of L with Al³⁺. The potentiality of L to be a distinguished probe to detect Al³⁺ ions was due to a chelation enhanced fluorescence (CHEF) effect, concomitant with noticeable fluorescent enhancement. A significant fluorescence enhancement at 533 nm was observed in ethanol–water (1:1, v/v) solution upon addition of Al³⁺ along with a distinct color change from yellow to white. Non-fluorescent ligand exposed highly sensitive turn-on fluorescent sensor behavior for selectively sensing Al³⁺ ions via 1:1 (ligand:metal) stoichiometry. The ligand’s specificity in the existence of other tested metal ions and anions indicated no observation in color change. The ligand-Al³⁺ complex formation was reversible upon addition of chelating agent EDTA. The ligand interacted with Al³⁺ ions with an association constant of K_a = 5 × 10⁴ M^?1. The limit of detection (LOD) was found to be 2.59 × 10^-7 M. The synthesized Schiff base could efficiently detect Al³⁺ ions as a fluorescent sensor.     

Trace Analysis of Heavy Metals with Two New Disodium Bisdithiocarbamates

Two chelating reagents, disodium N,N′-dibenzylethylenebisdithiocarbamate 1 and disodium piperazinebisdithiocarbamate 2, were synthesized and used to preconcentrate trace metals in aqueous samples. For analysis of Cu(II) using a UV-vis spectrometer, Beer's law was obeyed from 5.0 μg L^?1 to 6.0 mg L^?1 for reagent 1, and from 0.2 mg L^?1 to 6.0mg L^?1 for reagent. 2. The chelation ratio for reagent 1 to Cu(II) was determined to be 1:1, with a formation constant 1.0 × 10⁹ M^?l. The dependence of extraction and extraction efficiency of reagent 1 on pH was also studied with an atomic absorption spectrometer for nine heavy-metal ions-Cu(II), Fe(III), Pb(II), Co(II), Cr(VI), Ni(II), Zn(II), Mn(II) and Cd(II). Except Cr(VI) and Mn(II), the recovery yields of the other seven metal ions were almost quantitative at pH = 4 ? 6. The recovery was 82% for Cr(VI) at pH = 4 ? 5, and 52% for Mn(II) at pH = 6 ? 7.     

Polyamine-substituted epoxy-grafted silica for aqueous metal recovery

Glycidoxypropyltriethoxysilane (GPS) was used as a reactive silane to graft metal- complexing ligands onto silica gel in aqueous media under mild conditions. The synthesis entailed the reaction of GPS with silica gel, followed by grafting polyamine onto the epoxy functional group. GPS was added to silica gel in ethanol with 5 vol. % water and the mixture was air-dried for 24 h. Subsequently, excess amounts of polyamines: triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine were individually added to the silanised silica, followed by solvent evaporation and ovendrying at 60°C. The ligand-grafted silica gel particles showed a rapid heavy metal uptake in batch or flow-through experiments with capacities reaching 0.1 mmol g⁻¹ for copper, zinc, cadmium, or lead ions. Columns packed with the modified particles could be readily regenerated by acid-washing with only a small decrease in activity. The particles could be used for the colourimetric detection of heavy metal pollution or for pre-concentration for analytical purposes. Competition between Cu²⁺, Zn²⁺, Pb²⁺, and Cd²⁺ ions for the three synthesised silica showed that Cu²⁺ ions were adsorbed more strongly than the other metal ions. The general method developed can be applied to graft other molecules with terminal amino groups for other purposes.     

Determination of trace levels of metal ions in water samples by inductively coupled plasma mass spectrometry after on-line preconcentration on SO3-oxine CM-cellulose

Summary A method utilizing a miniature chelated ion-exchanger column of SO₃-oxine CM-cellulose has been developed to increase the sensitivity for multielement measurements by inductively coupled plasma mass spectrometry (ICP-MS). This matrix/analyte separation and preconcentration technique has been used to preconcentrate Mn, Co, Ni, Cu, Cd, and Pb from natural water samples. The multielement detection limits are in the low ppt (pg/mL) range. This FIA-ICP-MS method has been applied to the determination of various trace levels of metal ions in riverine reference material SLRS-2 and open ocean seawater reference material NASS-3.     

A novel method of the separation/preconcentration and determination of trace molybdenum(VI) in water samples using microcrystalline triphenylmethane loaded with salicyl fluorone

It is the first time that triphenylmethane was used as an adsorbent to preconcentrate and separate trace amount of molybdenum in water samples. The effects of different parameters, such as acidity, stirring time and various metal ions, the amounts of triphenylmethane and salicyl fluorine, etc. on the enrichment yield of molybdenum have been studied to optimize the experimental conditions. Under the optimum conditions, molybdenum can be adsorbed on the surface of microcrystalline triphenylmethane loaded with salicyl fluorone by the intermolecular action strength. The possible reaction mechanism for the enrichment of molybdenum was discussed in detail in this paper. Mo(VI) can be completely separated from Pb(II), Co(II), Cu(II), Cr(III), Ni(II), Hg(II), Zn(II), Cd(II), Fe(III) and Al(III) in the solution. The proposed method was successfully applied to the determination of trace amount of molybdenum in various water samples by spectrophotometry after preconcentration using microcrystalline triphenylmethane. The preconcentration factor is from 83 (500 ml water sample was enriched to 6.0 ml) to 166 (1000 ml water sample was enriched to 6.0 ml). The detection limit is 1.3 × 10⁻⁵ mg l⁻¹ and the linearity is maintained in the concentration range 3.8 × 10⁻³ to 0.36 mg l⁻¹ with a correlation coefficient of 0.9998. The recoveries are in the range of 93.5-104%. The relative standard deviation is 1.8-2.9%. Analytical results obtained with this novel method are very satisfactory.     

Total reflection X-ray fluorescence determination of rare earth elements in mineral water

A method is proposed for determination of lanthanum, cerium, praseodymium, neodymium, and samarium in mineral water by means of total-reflection X-ray fluorescence analysis. In this work, the combined technique of preconcentration of rare earth ions is used. This technique consists of coprecipitation of metal hydroxides on the collector (iron (III) hydroxide) and dispersive liquid–liquid microextraction of their complexes with 1-(2-pyridylazo)-2-naphthol by chloroform in the presence of ethanol. The use of the developed hybrid approach allows simultaneous determination of the mentioned metals in mineral water in the range n(10^–2–10¹) μg/L. The results of analysis of Arkhyz and Rychal-Su mineral waters by the proposed extraction–X-ray fluorescent method are confirmed by the literature data, obtained by inductively coupled plasma mass spectrometry.     

Anodic stripping voltammetry with mercury electrodes in extracts of cadmium,lead, thallium and indium diethyldithiocarbamate complexes and analysis of mixtures

The selectivity of the determination of traces of cadmium, lead, thallium and indium is improved by direct coupling of liquid/liquid extraction and anodic stripping voltammetry. Metals are extracted from aqueous solution to benzene or chloroform after the addition of sodium or zinc diethyldithiocarbamate. Stripping voltammetry of Cd, Tl and Pb at a hanging mercury drop electrode or mercury film electrode is done in benzene/methanol medium (1:1) with 0.1 M NaClO₄ as supporting electrolyte. For indium, the medium is chloroform/ethanol/water (1:4:1) with 0.005 M sodium acetate/0.06 M KBr/0.06 M HCl as supporting electrolyte. The complexes in acidic solution can be decomposed by mercury (II) ions, which provides useful shifts of deposition potentials. Calibration graphs are linear at concentrations of about 10^?7 M with a detection limit of 1×10^?8 M. The method is applied to determine a single metal in the presence of a large amount (1000-fold) of interfering metal.