8-Hydroxyquinoline anchored to silica gel via new moderate size linker: synthesis and applications as a metal ion collector for their flame atomic absorption spectrometric determination

The silica gel modified with (3-aminopropyl-triethoxysilane) was reacted with 5-formyl-8-hydroxyquinoline (FHOQ_x) to anchor 8-quinolinol ligand on the silica gel. It was characterised with cross polarisation magic angle spinning (CPMAS) NMR and diffuse reflectance infrared Fourier transformation (DRIFT) spectroscopy and used for the preconcentration of Cu(II), Pb(II), Ni(II), Fe(III), Cd(II), Zn(II) and Co(II) prior to their determination by flame atomic absorption spectrometry. The surface area of the modified silica gel has been found to be 227 m² g⁻¹ and the two pKa values as 3.8 and 8.0. The optimum pH ranges for quantitative sorption are 4.0–7.0, 4.5–7.0, 3.0–6.0, 5.0–8.0, 5.0–8.0, 5.0–8.0 and 4.0–7.0 for Cu, Pb, Fe, Zn, Co, Ni and Cd, respectively. All the metals can be desorbed with 2.5 mol l⁻¹ HCl or HNO₃. The sorption capacity for these metal ions is in range of 92–448.0 μmol g⁻¹ and follows the order Cd3, NaCl, NaBr, Na₂SO₄ and Na₃PO₄, glycine, sodium citrate, EDTA, humic acid and cations Ca(II), Mg(II), Mn(II) and Cr(III) in the sorption of all the seven metal ions are reported. The preconcentration factors are 150, 250, 200, 300, 250, 300 and 200 for Cd, Co, Zn, Cu, Pb, Fe and Ni, respectively and t_1/2 values <1 min except for Ni. The 95% extraction by batch method takes ≤25 min. The simultaneous enrichment and determination of all the metals are possible if the total load of the metal ions is less than sorption capacity. In river water samples all these metal ions were enriched with the present ligand anchored silica gel and determined with flame atomic absorption spectrometer (R.S.D.≤6.4%). Cobalt contents of pharmaceutical samples (vitamin tablet) were preconcentrated with the present chelating silica gel and estimated by flame AAS, with R.S.D.1.4%. The results are in the good agreement with the certified value, 1.99 μg g⁻¹ of the tablets. Iron and copper in certified reference materials (synthetic) SLRS-4 and SLEW-3 have been enriched with the modified silica gel and estimated with R.S.D.<5%.     

The efficacy of nitrosonaphthol functionalized XAD-16 resin for the preconcentration/sorption of Ni(II) and Cu(II) ions

Amberlite XAD-16 resin has been functionalized using nitrosonaphthol as a ligand and characterized employing elemental, thermogravimetric analysis and FT-IR spectroscopy. The sorption of Ni(II) and Cu(II) ions onto this functionalized resin is investigated and optimized with respect to the sorptive medium (pH), shaking speed and equilibration time between liquid and solid phases. The monitoring of the influence of diverse ions on the sorption of metal ions has revealed that phosphate, bicarbonate and citrate reduce the sorption up to 10–14%. The sorption data followed Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherms. The Freundlich parameters computed are 1/n = 0.56 ± 0.03 and 0.49 ± 0.05, A = 9.54 ± 1.5 and 6.0 ± 0.5 mmol g⁻¹ for Ni(II) and Cu(II) ions, respectively. D–R isotherm yields the values of X_m = 0.87 ± 0.07 and 0.35 ± 0.05 mmol g⁻¹ and of E = 9.5 ± 0.23 and 12.3 ± 0.6 kJ mol⁻¹ for Ni(II) and Cu(II) ions, respectively. Langmuir characteristic constants estimated are Q = 0.082 ± 0.005 and 0.063 ± 0.003 mmol g⁻¹, b = (4.7 ± 0.2) × 10⁴ and (7.31 ± 0.11) × 10⁴ l mol⁻¹ for Ni(II) and Cu(II) ions, respectively. The variation of sorption with temperature gives thermodynamic quantities of ΔH = −58.9 ± 0.12 and −40.38 ± 0.11 kJ mol⁻¹, ΔS = −183 ± 10 and −130 ± 8 J mol⁻¹ K⁻¹ and ΔG = −4.4 ± 0.09 and −2.06 ± 0.08 kJ mol⁻¹ at 298 K for Ni(II) and Cu(II) ions, respectively. Using kinetic equations, values of intraparticle transport and of first order rate constant have been computed for both the metal ions. The sorption procedure is utilized to preconcentrate these ions prior to their determination in tea, vegetable oil, hydrogenated oil (ghee) and palm oil by atomic absorption spectrometry using direct and standard addition methods.     

Speciation of Cr(III) and Cr(VI) in water after preconcentration of its 1,5-diphenylcarbazone complex on amberlite XAD-16 resin and determination by FAAS

A simple and sensitive method for the speciation, separation and preconcentration of Cr(VI) and Cr(III) in tap water was developed. Cr(VI) has been separated from Cr(III) and preconcentrated as its 1,5-diphenylcarbazone complex by using a column containing Amberlite XAD-16 resin and determined by FAAS. Total chromium has also been determined by FAAS after conversion of Cr(III) to Cr(VI) by oxidation with KMnO₄. Then, Cr(III) has been calculated by subtracting Cr(VI) from the total. The effect of acidity, amount of adsorbent, eluent type and flow rate of the sample solution on to the preconcentration procedure has been investigated. The retained Cr(VI) complex was eluated with 10 ml of 0.05 mol l⁻¹ H₂SO₄ solution in methanol. The recovery of Cr(VI) was 99.7±0.7 at 95% confidence level. The highest preconcentration factor was 25 for a 250 ml sample volume. The detection limit of Cr(VI) was found as 45 μg l⁻¹. The adsorption capacity of the resin was found as 0.4 mg g⁻¹ for Cr (VI). The effect of interfering ions has also been studied. The proposed method was applied to tap water samples and chromium species have been determined with the relative error <3%.     

Polymer supported catalysts for oxidation of phenol and cyclohexene using hydrogen peroxide as oxidant

Polymer supported transition metal complexes of N,N′-bis (o-hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by anchoring its amino derivative Schiff base (AHPHZ) on cross-linked (6 wt%) polymer beads and then loading iron(III), copper(II) and zinc(II) ions in methanol. The loading of HPHZ Schiff base on polymer beads was 3.436 mmol g⁻¹ and efficiency of complexation of polymer anchored HPHZ Schiff base for iron(III), copper(II) and zinc(II) ions was 83.21, 83.40 and 83.17%, respectively. The efficiency of complexation of unsupported HPHZ Schiff base for these metal ions was lower than polymer supported HPHZ Schiff base. The structural information obtained by spectral, magnetic and elemental analysis has suggested octahedral and square planar geometry for iron(III) and copper(II) ions complexes, respectively, with paramagnetic behavior, but zinc(II) ions complexes were tetrahedral in shape with diamagnetic behavior. The complexation with metal ions has increased thermal stability of polymer anchored HPHZ Schiff base. The catalytic activity of unsupported and polymer supported HPHZ Schiff base complexes of metal ions was evaluated by studying the oxidation of phenol (Ph) and epoxidation of cyclohexene (CH). The polymer supported metal complexes showed better catalytic activity than unsupported metal complexes. The catalytic activity of metal complexes was optimum at a molar ratio of 1:1:1 of substrate to oxidant and catalyst. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) in oxidation of phenol and epoxidation of cyclohexene was better with polymer supported metal complexes in comparison to unsupported metal complexes. The energy of activation for oxidation of phenol (22.8 kJ mol⁻¹) and epoxidation of cyclohexene (8.9 kJ mol⁻¹) was lowest with polymer supported complexes of iron(III) ions than polymer supported Schiff base complexes of copper(II) and zinc(II) ions.     

Cellulose based macromolecular chelator having pyrocatechol as an anchored ligand: synthesis and applications as metal extractant prior to their determination by flame atomic absorption spectrometry

Pyrocatechol is immobilized on cellulose via ---NH---CH₂---CH₂---NH---SO₂---C₆H₄---N=N--- linker and the resulting macromolecular chelator characterized by IR, TGA, CPMAS ¹³C NMR and elemental analyses. It has been used for enrichment of Cu(II), Zn(II), Fe(III), Ni(II), Co(II), Cd(II) and Pb(II) prior to their determination by flame atomic absorption spectrometry (FAAS). The pH ranges for quantitative sorption (98.0–99.4%) are 4.0–7.0, 5.0–6.0, 3.0–4.0, 5.0–7.0, 5.0–8.0, 7.0–8.0 and 4.0–5.0, respectively. The desorption was found quantitative with 0.5 mol dm⁻³ HCl/HNO₃ (for Pb). The sorption capacity of the matrix for the seven metal ions has been found in the range 85.3–186.2 μmol g⁻¹. The optimum flow rate of metal ion solution for quantitative sorption of metal onto pyrocatechol functionalized cellulose as determined by column method, is 2–6 cm³ min⁻¹, whereas for desorption it is 2–4 cm³ min⁻¹. The tolerance limits for NaCl, NaBr, NaI, NaNO₃, Na₂SO₄, Na₃PO_4, humic acid, EDTA, ascorbic acid, citric acid, sodium tartrate, Ca(II) and Mg(II) in the sorption of all the seven metal ions are reported. Ascorbic acid is tolerable up to 0.8 mmol dm⁻³ with Cu and Pb where as sodium tartrate does not interfere up to 0.6 mmol dm⁻³ with Pb. There is no interference of NaBr, NaCl and NaNO₃ up to a concentration of 0.5 mol dm⁻³, in the sorption of Cu(II), Cd(II) and Fe(III) on to the chelating cellulose matrix The preconcentration factors are between 75 and 300 and t_1/2 values ≤5 min for all the metal ions. Simultaneous sorption of Cu, Zn, Ni and Co is possible at pH 5.0 if their total concentration does not exceed lowest sorption capacity. The present matrix coupled with FAAS has been used to enrich and determine the seven metal ions in river and tap water samples (relative standard deviation (R.S.D.) 1.05–7.20%) and synthetic certified water sample SLRS-4 (NRC, Canada) with R.S.D. 2.03%. The cobalt present in pharmaceutical vitamin tablets was also preconcentrated on the modified cellulose and determined by FAAS (R.S.D. 1.87%).     

Preparation of novel ion exchange polyurethane foam and its application for separation and determination of palladium in environmental samples

The new strong anion exchanger (PUFIX) from polyurethane foam was prepared by coupling of the primary amine of the foam matrix with ethyl iodide. PUFIX was characterized using different tools (IR spectra, elemental analysis, density and thermal analysis). The sorption properties of the new anion exchanger (PUFIX) and chromatographic behaviour for separation and determination of palladium(II) ions at low concentrations from aqueous iodide or thiocyanate media were investigated by a batch and dynamic processes. The maximum sorption of Pd(II) was in the pH range of 0.3–2. The kinetics of sorption of the Pd(II) by the PUFIX was found to be fast with average values of half-life of sorption (t_1/2) of 3.32 min. The variation of the sorption of Pd(II) with temperature gives average values of ΔH, ΔS, ΔG and ΔE to be −38.3 kJ mol⁻¹, −100.7 J K⁻¹ mol⁻¹, −8.3 and 11.8 kJ mol⁻¹, respectively. The sorption capacity of PUFIX was 1.69 mmol g⁻¹ for Pd(II), preconcentration factors of values ≈250 and the recovery 99–100% were achieved (R.S.D. ≈ 1.24%). The lower detection limit, 1.28 ng mL⁻¹ was evaluated using spectrophotometric method (R.S.D. ≈ 2.46%).     

Determination of soluble phosphates in water samples using ytterbium(III) and dynamic measurements of light scattering intensity at long wavelength

A selective and fast method has been developed for the determination of phosphates by measuring the formation of ytterbium(III) phosphate through the variation of the light scattering intensity with time. The low solubility of this compound causes an efficient dispersion of the radiation at 490 nm, which is measured at 980 nm using the second-order grating effect. This approach minimizes potential background signals from the sample matrix. The initial rate of the system is automatically obtained in only 0.5 s by stopped-flow mixing technique. The variable optimization study has been carried out using univariate and multivariate methods. The dynamic range of the calibration graph is 0.09–7.9 mmol L⁻¹ (Pearson's correlation coefficient = 0.9999) and the detection limit is 0.03 mmol L⁻¹. The precision of the method, expressed as relative standard deviation, is 2.3%. The study of the potential interference of different inorganic anions showed that arsenate is the main interferent, although it is tolerated in a molar ratio of 5.5. The method has been satisfactorily applied to the determination of soluble phosphates in tap, ground and river water using a previous preconcentration step with a Dowex 1 (1 × 4–400) anionic resin. A 500-fold concentration has been achieved, which has allowed to decrease the detection limit up to 60 mmol L⁻¹. The recovery range is 97.5–102.5%. The results obtained are consistent with those obtained with the standard molybdenum blue method.     

Extraction of Pb(II), Cd(II), and Hg(II) from aqueous solution by nitrogen and thiol functionality grafted to silica gel measured by calorimetry

The reaction of ethylene sulfide with 3-aminopropyltrimethoxysilane gave a new silylating agent, which was anchored onto a silica surface via the sol–gel procedure. This surface displayed a chelating moiety containing nitrogen and two sulfur basic centers potentially capable of extracting cations from aqueous solutions. The process of metal extraction was followed by a batch method, and fitted to a modified Langmuir equation. The maximum adsorption capacities found were: 2.06 ± 0.01, 3.72 ± 0.02, and 5.14 ± 0.02 mmol g⁻¹ for Pb(II), Cd(II), and Hg(II), respectively. The enthalpies of bending are: −1.16 ± 0.04, −3.60 ± 0.10, and −8.94 ± 0.03 kJ mol⁻¹ for Cd(II), Pb(II), and Hg(II), respectively. The Gibbs free energies of binding agree with the spontaneity of the proposed reactions between cations and basic centers.     

A new chelating sorbent for metal ion extraction under high saline conditions

A new chelating polymeric sorbent was developed by functionalizing Amberlite XAD-16 with 1,3-dimethyl-3-aminopropan-1-ol via a simple condensation mechanism. The newly developed chelating matrix offered a high resin capacity and faster sorption kinetics for the metal ions such as Mn(II), Pb(II), Ni(II), Co(II), Cu(II), Cd(II) and Zn(II). Various physio-chemical parameters like pH-effect, kinetics, eluant volume and flow rate, sample breakthrough volume, matrix interference effect on the metal ion sorption have been studied. The optimum pH range for the sorption of the above mentioned metal ions were 6.0–7.5, 6.0–7.0, 8.0–8.5, 7.0–7.5, 6.5–7.5, 7.5–8.5 and 6.5–7.0, respectively. The resin capacities for Mn(II), Pb(II), Ni(II), Co(II), Cu(II), Cd(II) and Zn(II) were found to be 0.62, 0.23, 0.55, 0.27, 0.46, 0.21 and 0.25 mmol g⁻¹ of the resin, respectively. The lower limit of detection was 10 ng ml⁻¹ for Cd(II), 40 ng ml⁻¹ for Mn(II) and Zn(II), 32 ng ml⁻¹ for Ni(II), 25 ng ml⁻¹ for Cu(II) and Co(II) and 20 ng ml⁻¹ for Pb(II). A high preconcentration value of 300 in the case of Mn(II), Co(II), Ni(II), Cu(II),Cd(II) and a value of 500 and 250 for Pb(II) and Zn(II), respectively, were achieved. A recovery of >98% was obtained for all the metal ions with 4 M HCl as eluting agent except in the case of Cu(II) where in 6 M HCl was necessary. The chelating polymer showed low sorption behavior to alkali and alkaline earth metals and also to various inorganic anionic species present in saline matrix. The method was applied for metal ion determination from water samples like seawater, well water and tap water and also from green leafy vegetable, from certified multivitamin tablets and steel samples.     

Silica gel ethyleneimine and its adsorption capacity for divalent Pb, Cd, and Hg

Activated silica gel was directly modified with a cyclic molecule, ethyleneimine, yielding a surface with various nitrogen basic centers, ≡Sil–O(CH₂CH₂NH)_nCH₂CH₂NH₂. Infrared spectroscopy, ¹³C NMR, thermal, and elemental analyses confirmed the covalent attachment of the organic species onto the silica matrix. The purpose of this paper is to describe the interaction involving the grafted species on silica surface with the divalent heavy cations, Pb(II), Cd(II), and Hg(II), from aqueous solutions at room temperature. The process of metal extraction was followed by the batch method and the order of the maximum extraction capacities found was: 1.27 ± 0.04, 1.02 ± 0.02, and 0.98 ± 0.01 mmol g⁻¹ for Pb(II), Cd(II), and Hg(II) chlorides, respectively. These interactions were followed by calorimetric titration. The enthalpies of these processes are: −3.05 ± 0.02, −1.09 ± 0.01, and −9.88 ± 0.03 kJ mol⁻¹ for Pb(II), Cd(II), and Hg(II), respectively. The standard molar Gibbs free energies are in agreement with the spontaneity of the proposed reactions between cation and basic center.     

Organically modified silica gel and flame atomic absorption spectrometry: employment for separation and preconcentration of nine trace heavy metals for their determination in natural aqueous systems

A 5-formyl-3-(1′-carboxyphenylazo) salicylic acid-bonded silica gel (FCPASASG) chelating adsorbent was synthesized according to a very simple and rapid one step reaction between aminopropyl silica gel (APSG) and 5-formyl-3-(1′-carboxyphenylazo) salicylic acid (FCPASA) and its adsorption characteristics were studied in details. Nine trace metals viz.: Cd(II), Zn(II), Fe(III), Cu(II), Pb(II), Mn(II), Cr(III), Co(II) and Ni(II) can be quantitatively adsorbed by the adsorbent from natural aqueous systems at pH 7.0–8.0. The adsorbed metal ions can be readily desorbed with 1 M HNO₃ or 0.05 M Na₂EDTA. The distribution coefficient, K_d and the percentage concentration of the investigated metal ions on the adsorbent at equilibrium, C_M,_eqm % (Recovery, R%) were studied as a function of experimental parameters. The logarithmic values of the distribution coefficient, logK_d, are 3.7–6.4. Some foreign ions caused little interference in the preconcentration and determination of the investigated nine metals by flame atomic absorption spectrometry (AAS).The adsorption capacity of FCPASASG was 0.32–0.43 meq g⁻¹. C and N elemental analyses of the adsorbent (FCPASASG) allowed us to calculate a surface converge of 0.82 mmol g⁻¹. This value compares well with the best values reported for the azo compounds. The adsorbent and its formed metal chelates were characterized by IR (absorbance and/or reflectance) and UV spectrometry, potentiometric titrations and thermogravimetric analysis (TGA and DTG). The mode of chelation between the FCPASASG adsorbent and the investigated metal ions is proposed to be due to reaction of those metal ions with the salicylic and/or the carboxyphenylazo chelation centers of the FCPASASG adsorbent. Nanogram concentrations (0.07–0.14 ng ml⁻¹) of Cd(II), Zn(II), Fe(III), Pb(II), Cr(III), Mn(II), Cu(II), Co(II) and Ni(II) can be determined reliably with a preconcentration factor of 100.     

Nickel determination in saline matrices by ICP-AES after sorption on Amberlite XAD-2 loaded with PAN

In the present paper, a solid phase extraction system for separation and preconcentration of nickel (ng g⁻¹) in saline matrices is proposed. It is based on the adsorption of nickel(II) ions onto an Amberlite XAD-2 resin loaded with 1-(2-pyridylazo)-2-naphthol (PAN) reagent. Parameters such as the pH effect on the nickel extraction, the effect of flow rate and sample volume on the extraction, the sorption capacity of the loaded resin, the nickel desorption from the resin and the analytical characteristics of the procedure were studied. The results demonstrate that nickel(II) ions, in the concentration range 0.10–275 μg l⁻¹, and pH 6.0–11.5, contained in a sample volume of 25–250 ml, can be extracted by using 1 g Amberlite XAD-2 resin loaded with PAN reagent. The adsorbed nickel was eluted from the resin by using 5 ml 1 M hydrochloric acid solution. The extractor system has a sorption capacity of 1.87 μmol nickel per g of Amberlite XAD-2 resin loaded with PAN. The precision of the method, evaluated as the R.S.D. obtained after analyzing a series of seven replicates, was 3.9% for nickel in a concentration of 0.20 μg ml⁻¹. The proposed procedure was used for nickel determination in alkaline salts of analytical grade and table salt, using an inductively coupled plasma atomic emission spectroscopy technique (ICP-AES). The standard addition technique was used and the recoveries obtained revealed that the proposed procedure shows good accuracy.     

Selective adsorption, pre-concentration and matrix elimination for the determination of Pb(II), Cd(II), Hg(II) and Cr(III) using 1,5,9,13-tetrathiacyclohexadecane-3,11-diol anchored poly (p-chloromethylstyrene-ethyleneglycoldimethacrylate) microbeads

Poly(p-chloromethylstyrene-ethyleneglycoldimethacrylate) polymeric microbeads, poly(p-CMS-EGDMA), were synthesized and 1,5,9,13-tetrathiacyclohexadecane-3,11-diol (S4HD) was attached chemically onto the polymeric microbeads. Characterization of all microbeads was done by Fourier transform-infrared spectrometry (FT-IR) and elemental analyzer. The amount of attached 1,5,9,13-tetrathiacyclohexadecane-3,11-diol to the polymer was found to be 2.23 mmol g⁻¹ polymers. The ligand attached microbeads, poly(p-CMS-EGDMA-S4HD), were used to examine the adsorption capacity of Pb(II), Cd(II), Hg(II) and Cr(II) ions for recovery, pre-concentration and the matrix elimination by changing the pH and the initial metal ion concentrations and also adsorption kinetics of the studied metal ions was determined. Pre-concentration factors for the studied toxic metal ions were found to be more than 500-fold and recovery was between 92 and 106%. In the drinking, lake, tap and sea-water samples from water lands, ultra-trace toxic metal ion concentrations were determined easily by using ligand modified microbeads after pre-concentration because of the high pre-concentration factor and easily matrix elimination using ligand modified microbeads. Reference sea-water material was used for the validation of the method and it was found that recovery, pre-concentration and the matrix elimination were performed perfectly. For the desorption of the toxic metal ions, 3 M HCl containing 0.8 M thiourea was used and desorption ratio was obtained more than 96%.     

Pyrocatechol Violet immobilized Amberlite XAD-2: synthesis and metal-ion uptake properties suitable for analytical applications

Amberlite XAD-2 has been functionalized by coupling it, through the ---N=N--- group, with Pyrocatechol Violet (PV), and the resulting resin has been characterized by elemental analysis, thermogravimetric analysis (TGA) and IR spectra. The resin has been used for preconcentrating Zn(II), Cd(II), Pb(II) and Ni(II) ions prior to their determination by flame atomic absorption spectrometry. The optimum pH values for quantitative sorption are 5, 5–7, 4, and 3 for Zn, Cd, Pb and Ni, respectively. The four metals can be desorbed (recovery ˜98%) with 4 M HNO₃; also, 4 M HCl is equally suitable except for Zn. The sorption capacity of the resin is 1410, 1270, 620 and 1360 μg g⁻¹ resin for Zn, Cd, Ni and Pb, respectively. The effect of F⁻, Cl⁻, NO₃⁻, SO₄²⁻ and PO₄³⁻ on the sorption of these four metal ions has been investigated. They are tolerable in the range 0.01–0.20 M, for Pb. In the sorption of Zn(II) and Ni(II), the tolerance limits of all these ions are upto 0.01 M, whereas for Cd(II), F⁻, NO₃⁻, and PO₄³⁻ have been found to be tolerable upto 0.50, 0.10 and 0.10 M, respectively. The preconcentration factors are 60, 50, 23 and 18 for Zn, Cd, Pb and Ni, respectively. Simultaneous collection and determination of the four metals are possible. Cations commonly present in drinking water do not affect the sorption of either metal ion if present at a concentration level similar to that of water. The method has been applied to determine Zn, Ni and Pb content of well-water samples (RSD ≤9%).     

Silica gel modified with N-(3-propyl)-O-phenylenediamine: functionalization, metal sorption equilibrium studies and application to metal enrichment prior to determination by flame atomic absorption spectrometry.

The use of the chemically modified silica gel N-(3-propyl)-O-phenylenediamine (SiG-NPPDA) adsorbent, for the preconcentration and separation of trace heavy metals, was described. SiG-NPPDA sorbs quantitatively (90-100% recovery) trace amounts of nine heavy metals, viz., Cd(II), Zn(II), Fe(III), Cu(II), Pb(II), Mn(II), Cr(III), Co(II) and Ni(II) at pH 7-8. The sorption capacity varies from 350 to 450 micromol g(-1). Desorption was found to be quantitative with 1-2 M HNO3 or 0.05 M Na2EDTA. The distribution coefficient, Kd and the percentage concentration of the investigated metal ions on the adsorbent at equilibrium, C(M,eqm)% (Recovery, R%), were studied as a function of experimental parameters. The logarithmic values of the distribution coefficient, log Kd, ranges between 4.0 and 6.4. Some foreign ions caused little interference in the preconcentration and determination of the investigated nine metals by flame atomic absorption spectrometry (AAS). The adsorbent and its formed metal chelates were characterized by IR (absorbance and/or reflectance), potentiometric titrations and thermogravimetric analysis (TGA and DTG). The mode of chelation between the SiG-NPPDA adsorbent and the investigated metal ions is proposed to be due to the reaction of the investigated metal ions with the two nitrogen atoms of the SiG-NPPDA adsorbent. The present adsorbent coupled with flame AAS has been used to enrich and determine the nine metal ions in natural aqueous systems and in certified reference materials (RSD < or = 5%). The copper, iron, manganese and zinc present in some pharmaceutical vitamin samples were also preconcentrated on SiG-NPPDA adsorbent and determined by flame AAS (RSD < or = 4.2%). Nanogram concentrations (0.07-0.14 ng ml(-1)) of Cd(II), Zn(II), Fe(III), Pb(II), Cr(III), Mn(II), Cu(II), Co(II) and Ni(II) can be determined reliably with a preconcentration factor of 100.     

Nanometer-size titanium dioxide microcolumn on-line preconcentration of trace metals and their determination by inductively coupled plasma atomic emission spectrometry in water

A new method using a microcolumn packed with nanometer TiO₂ as solid-phase extractant has been developed for the simultaneous preconcentration of trace amounts of Cu, Mn, Cr and Ni prior to their measurements by inductively coupled plasma atomic emission spectrometry (ICP-AES). Effects of pH, sample flow rate and volume, elution solution and interfering ions on the recovery of the analytes have been investigated. The adsorption capacity of nanometer TiO₂ was found as 0.108, 0.149, 0.039 and 0.034 mmol g⁻¹ for Cu, Cr, Mn and Ni, respectively. The separation of analytes can be achieved from water samples with a concentration factor of 50 times. The method has been applied for the determination of trace elements in biological sample and lake water with satisfactory results.     

Atomic absorption spectrophotometric determination of trace copper in waters, aluminium foil and tea samples after preconcentration with 1-nitroso-2-naphthol-3,6-disulfonic acid on Ambersorb 572

An atomic absorption spectrophotometric method for the determination of trace copper after adsorption of its 1-nitroso-2-naphthol-3,6-disulfonic acid chelate on Ambersorb 572 has been developed. This chelate is adsorbed on the adsorbent in the pH range 1–8. The copper chelate is eluted with 5 ml of 0.1 mol l⁻¹ potassium cyanide and determined by flame atomic absorption spectrometry (FAAS). The selectivity of the proposed procedure was also evaluated. Results show that iron(III), zinc(II), manganese(II) and cobalt(II) at the 50 μg l⁻¹ level and sodium(I), potassium(I), magnesium(II), calcium(II) and aluminium(III) at the 1000 μg l⁻¹ level did not interfere. A high enrichment factor, 200, was obtained. The detection limit (3σ) of copper was 0.34 μg l⁻¹. The precision of the method, evaluated by seven replicate analyses of solutions containing 5 μg of copper was satisfactory and the relative standard deviation was 1.7%. The adsorption of copper onto Ambersorb 572 can formally be described by a Langmuir equation with a maximum adsorption capacity of 14.3 mg g⁻¹ and a binding constant of 0.00444 l mg⁻¹. The accuracy of the method is confirmed by analysing tomatoes leaves (NIST 1573a) and lead base alloy (NBS 53e). The results demonstrated good agreement with the certified values. This procedure was applied to the determination of copper in waters (tap, river and thermal waters), aluminium foil and tea samples.     

Synthesis and efficiency of an epoxy-tannin chelating resin for preconcentrating and separating various rare elements

A new epoxy-tannin chelating resin was synthesized from epoxy resin and used for the preconcentration and separation of rare elements. The acidity, rate, reuse, capacity and interference on the adsorption of ions on the resin as well as the conditions of desorption of these ions from the resin were investigated by means of inductively coupled plasma atomic emission spectrometry (ICP-AES). The composition of the resin and mechanism of enrichment for some ions were discussed. The results show that the relative standard deviations for the determination of 50 ng ml⁻¹ Ga(III), In(III), Bi(III) and Sn(IV), 10 ng ml⁻¹ La(III), Y(III), Cr(III), Ti(IV) and V(V) and 1.0 ng ml⁻¹ Be(II) were in the range of 0.5–4.5%. The contents of these elements in a sample solution from a smelter determined by the new method were in agreement with those values obtained by Zeeman atomic absorption spectrometry with an average error <3.4%.     

Removal and preconcentration of lead(II), cadmium(II) and chromium(III) ions from wastewater samples using surface functionalized magnetite nanoparticles

The potential removal and preconcentration of lead(II), cadmium(II), and chromium(III) ions from wastewaters were investigated and explored. Magnetite nanoparticles were chemically modified with p-nitro aniline. The aniline-coated magnetite nanoparticles (ANMNPs) were fully characterized by FT-IR, XRD, SEM, and TEM measurements. Batch studies were performed to address various experimental parameters for the removal and determination of these ions. ANMNPs showed high tendency to investigated metal ions, in this order: Cr(III) > Cd(II) > Pb(II), owing to the strong contribution of surface loaded aniline. The potential applications of ANMNPs adsorbent for removal and preconcentration of Pb(II), Cr(III), and Cd(II) from wastewaters as well as drinking tap water samples were successfully accomplished giving recovery values of (98–101 %), without any noticeable interference of the wastewater or drinking tap water matrices.     

Amberlite XAD-2 functionalized with o-aminophenol: synthesis and applications as extractant for copper(II), cobalt(II), cadmium(II), nickel(II), zinc(II) and lead(II)

A stable chelating resin matrix was synthesized by covalently linking o-aminophenol (o-AP) with the benzene ring of the polystyrene–divinylbenzene resin, Amberlite XAD-2, through a –N=N– group. Elemental analyses, thermogravimetric analysis (TGA) and infrared spectra have characterized the resulting chelating resin. It has been used to preconcentrate Cu²⁺, Cd²⁺, Co²⁺, Ni²⁺, Zn²⁺ and Pb²⁺, prior to their determination by flame atomic absorption spectrometry. The optimum pH values for quantitative sorption of Cu, Cd, Co, Ni, Zn and Pb are 6.2–7.4, 5.6–7.2, 5.6–9.0, 6.0–9.0, 5.7–7.0 and 5.0–6.0, respectively. These metals are desorbed (recovery 91–98%) with 4 mol dm⁻³ HNO₃. The sorption capacity of the resin is 3.37, 3.42, 3.29, 3.24, 2.94 and 3.32 mg of metal g⁻¹ of resin, respectively, for Cu, Cd, Co, Ni, Zn and Pb. The effect of NaF, NaCl, NaNO₃, Na₂SO₄, and Na₃PO₄ on the sorption of these metal ions has been investigated. These electrolytes are tolerable up to 0.01 mol dm⁻³ in case of all the metal ions, except Cl⁻ which is tolerable even up to 0.1 mol dm⁻³ for Zn and 1.0 mol dm⁻³ for Pb. The preconcentration factor for Cu, Cd, Co, Ni, Zn and Pb are 50, 50, 100, 65, 40 and 40 (concentration level 10–25 μg dm⁻³) respectively. Simultaneous enrichment of the six metals is possible. The method has been applied to determine Cu, Cd, Co, Ni, Zn and Pb content in well water samples (RSD≤8%).