Solid phase extraction of Pb(II) in water samples using a new hybrid inorganic-organic mesoporous silica prior to its determination by FAAS

A mesoporous silica has been chemically modified with 5-mercapto-1-methyltetrazole. The newly synthesized material was characterized by powder X-ray diffraction, N₂ adsorption, FT-IR, ¹³C-NMR spectroscopy and elemental analysis, and used to preconcentrate Pb(II) from aqueous solutions. The effect of several variables on the adsorption capacity (i.e. stirring time, pH, interfering ions, presence of other heavy metals in the medium, etc.) has been studied using batch and column techniques. The adsorption capacity of the material followed the order: Pb(II) >> Cu(II) > Cd(II) >>Mn(II) > Ni(II) > Co(II). In column experiments a pre-concentration factor of 200 was obtained for Pb(II). Spiked tap water, mineral water and river water were used for the preconcentration and determination of Pb(II) by flame atomic absorption spectrometry, and a 101–103% recovery was obtained. The limit of detection and quantification values of the method were found to be 2.22·10^?6 mM and 8.20·10^?6 mM, respectively. The relative standard deviation for four preconcentration experiments was found to be ≤9% in all cases.     

Solid phase extraction of Pb(II) and Cd(II) as 2,9 dimethyl-4,7-diphenyl-1,10-phenanthroline chelates on activated carbon cloth in environmental samples and their determination by flame atomic absorption spectrometry

A solid-phase extraction procedure for Pb(II) and Cd(II) as 2,9 dimethyl-4,7-diphenyl-1,10-phenanthroline complexes on activated carbon cloth (ACC) has been established. In the determination step, flame atomic absorption spectrometry (FAAS) was used. The optimum conditions for pH, type and volume of eluent, volume of sample solution, flow rates of eluent, sample solution and matrix effect were determined. For quantitative recovery of the analyte ions, refereed optimum values are as follows: amount of ACC, 0.4 g; pH, 6.0 and eluent, 10 mL 3 M HNO₃. To test the accuracy of the method, a certified reference material (CRM) analysis and add-recovery methods were performed. The developed method was applied for the determination of the analyte elements in water and vegetable samples.     

A magnetic metal-organic framework as a new sorbent for solid-phase extraction of copper(II), and its determination by electrothermal AAS

We report on the synthesis of Fe₃O₄-functionalized metal-organic framework (m-MOF) composite from Zn(II) and 2-aminoterephthalic acid by a hydrothermal reaction. The magnetic composite is iso-reticular and was characterized by FTIR, X-ray diffraction, SEM, magnetization, and TGA. The m-MOF was then applied as a sorbent for the solid-phase extraction of trace levels of copper ions with subsequent quantification by electrothermal AAS. The amount of sorbent applied, the pH of the sample solution, extraction time, eluent concentration and volume, and desorption time were optimized. Under the optimum conditions, the enrichment factor is 50, and the sorption capacity of the material is 2.4 mg g^?1. The calibration plot is linear over the 0.1 to 10 μg L^?1 Cu(II) concentration range, the relative standard deviation is 0.4 % at a level of 0.1 μg L^?1 (for n?=?10), and the detection limit is as low as 73 ng L^?1. We consider this magnetic MOF composite to be a promising and highly efficient material for the preconcentration of metal ions.

Fast and selective magnetic solid phase extraction of trace Cd, Mn and Pb in environmental and biological samples and their determination by ICP-MS

We have immobilized iminodiacetic acid on mesoporous Fe₃O₄@SiO₂ microspheres and used this material for efficient and cost effective method of magnetic solid phase extraction (SPE) of trace levels of Cd, Mn and Pb. The microspheres were characterized by infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The loaded microspheres can be easily separated from the aqueous sample solution by applying an external magnetic field. The effects of pH, sample volume, concentration and volume of eluent, and of interfering ions were investigated in detail. The method has detection limit of 0.16, 0.26 and 0.26?ng?L^?1 for the ions of Cd, Mn and Pb, respectively, and the relative standard deviations (RSDs, c?=?1???g?L^?1, n?=?7) are 4.8%, 4.6% and 7.4%. The method was successfully applied to the determination of these metals in biological and environmental samples using ICP-MS. Two certified reference materials were analyzed, and the results coincided well with the certified values.

Simultaneous determination of Cd(II), Cu(II) and Pb(II) in surface waters by solid phase extraction and flow injection analysis with spectrophotometric detection

A method for heavy metal monitoring using spectrophotometric detection is presented. Traces of Cu(II), Pb(II) and Cd(II) at the low microg l(-1) level can be determined simultaneously after both selective removal of metal interferences and preconcentration using 'extraction chromatographic resins'. Lewatit TP807'84, which contains di(2,4,4-trimethylpentyl)phosphinic acid as active component, was used as solid adsorbent. Two minicolumns containing this resin were used: one at pH 3.2 for the removal of interferences, such as Zn(II) and Fe(III), and the other at pH 5.5 for the selective preconcentration of the target analytes. Spectrophotometric determination used FIA methodology with sulfarsazene as chromogenic reagent and partial least-squares multivariate calibration. The method was successfully applied to the analysis of surface waters from the Llobregat river and ground water samples from wells in the Guadiamar basin. Accuracy, expressed in terms of recoveries, was in the range 80-120% and relative standard deviations were below 10%.     

Solid phase extraction of Cd(II), Pb(II), Zn(II) and Ni(II) from food samples using multiwalled carbon nanotubes impregnated with 4-(2-thiazolylazo)resorcinol

Multiwalled carbon nanotubes were impregnated with 4-(2-thiazolylazo)resorcinol and used for the separation and preconcentration of Cd(II), Pb(II), Zn(II) and Ni(II) ions from food samples. The analytes were quantitatively recovered at pH 7.0 and eluted with 3?mol?L^?1 acetic acid. The effects of pH value, flow rate, eluent type and sample volume on the recoveries, and the effects of alkali, earth alkali and transition metals on the retention of the analytes were studied. The method was validated using the standard certified reference materials SRM 1570A (spinach leaves) and IAEA 336 (lichen), and the results were found to be compatible with the certified values of reference materials. The new enrichment procedure was applied to the determination of these ions in various food samples.

Solid phase extraction and diffusive gradients in thin films techniques for determination of total and labile concentrations of Cd(II), Cu(II), Ni(II) and Pb(II) in Black Sea water

Total dissolved and labile concentrations of Cd(II), Cu(II), Ni(II) and Pb(II) were determined at six locations of the Bourgas Gulf of the Bulgarian Black Sea coast. Solid phase extraction procedure based on monodisperse, submicrometer silica spheres modified with 3-aminopropyltrimethoxysilane followed by the electrothermal atomic absorption spectrometry (ETAAS) was developed and applied to quantify the total dissolved metal concentrations in sea water. Quantitative sorption of Cd, Cu, Ni and Pb was achieved in the pH range 7.5–8, for 30?min, adsorbed elements were easily eluted with 2?mL 2?mol?L^?1 HNO₃. Since the optimal pH for quantitative sorption coincides with typical pH of Black Sea water (7.9–8.2), on-site pre-concentration of the analytes without any additional treatment was possible. Detection limits achieved for total dissolved metal quantification were: Cd 0.002?µg?L^?1, Cu 0.005?µg?L^?1, Ni 0.03?µg?L^?1, Pb 0.02?µg?L^?1 and relative standard deviations varied from 5–13% for all studied elements (for typical Cd, Cu, Ni and Pb concentrations in Black Sea water). Open pore diffusive gradients in thin films (DGT) technique was employed for in-situ sampling and pre-concentration of the sea water and in combination with ETAAS was used to determine the proportion of dynamic (mobile and kinetically labile) species of Cd(II), Cu(II), Ni(II) and Pb(II) in the sea water. Obtained results showed strong complexation for Cu and Pb with sea water dissolved organic matter. The ratios between DGT-labile and total dissolved concentrations found for Cu(II) and Pb(II) were in the range 0.2–0.4. For Cd and Ni, these ratios varied from 0.6 to 0.8, suggesting higher degree of free and kinetically labile species of these metals in sea water.     

Ultra-trace determination of Pb(II) and Cd(II) in drinking water and alcoholic beverages using homogeneous liquid-liquid extraction followed by flame atomic absorption spectrometry

The determination of Pb(II) and Cd(II) in different sample matrices, including drinking water, distilled spirits and fruit wine, was carried out by flame atomic absorption spectrometry (FAAS) after pre-concentration using homogeneous liquid-liquid extraction (HLLE). First, the HLLE method was optimised with lead diethyldithiocarbamate (Pb-DDTC) complex which was extracted with a perfluorooctanoate anion (PFOA^?) dissolved in lithium hydroxide under acidic conditions. The optimum extraction conditions, using 0.01 M DDTC, 0.05 M PFOA^?, 3 M HCl and 1 mL of 30 vol. % acetone, were obtained. The Pb-DDTC complex in the nitric acid digest of the samples (50–150 mL) was extracted quantitatively into a drop of 100 μL of sediment phase. The sediment phase dissolved in 1 vol. % HNO₃ with at least 3–5 mL of the final volume was then determined by FAAS, affording a pre-concentration factor of 10–50. Hence, the HLLE method afforded an increase in both sensitivity and selectivity for the metal determination by conventional FAAS, resulting in ultra-trace level detection of Pb(II) in all samples analysed (drinking water, 9.2–23 ng mL^?1; distilled spirits, 23–50 ng mL^?1; fruit wine, 24–53 ng mL^?1). In addition, the proposed method could successfully be applied to Cd(II) determination in these samples.     

Solid phase extraction of trace amount of Cu(II) using functionalized-graphene

A novel and selective method for the fast determination of trace amounts of Cu(II) ions in water samples has been developed. The first organic-solution-processable functionalized-graphene (SPF-Graphene) hybrid material with porphyrins, porphyrin-graphene nanohybrid, 5-(4-aminophenyl)-10, 15, 20-triphenyl porphyrin and its photophysical properties including optical (TPP) and grapheme oxide molecules covalently bonded together via an amide bond (TPP-NHCO-SPFGraphene) were used as absorbent for extraction of Cu(II) ions by solid phase extraction method. The complexes were eluted with HNO₃ (2 M) 10% (vol/vol) methanol in acetone and determined the analyte by flame atomic absorption spectrometry. The procedure is based on the selective formation of Cu(II) at optimum pH by elution with organic eluents and determination by flame atomic absorption spectrometry. The method is based on complex formation on the surface of the ENVI-18 DISK? disks modified porphyrin-graphene nanohybrid, 5-(4-aminophenyl)-10,15,20-triphenyl porphyrin (TPP) and grapheme oxide molecules covalently bonded together via an amide bond (TPP-NHCO-SPFGraphene) followed by stripping of the retained species by minimum amounts of appropriate organic solvents. The elution is efficient and quantitative. The effect of potential interfering ions, pH, TPP-NHCO-SPFGraphene, amount, stripping solvent, and sample flow rate were also investigated. Under the optimal experimental conditions, the break-through volume was found to about 1000 mL providing a preconcentration factor of 600. The maximum capacity of the disks was found to be 398 ± 3 μg for Cu²⁺. The limit of detection of the proposed method is 5 ng per 1000 mL. The method was applied to the extraction and recovery of copper in different water samples.     

A pillar-layered Cd(II) metal-organic framework for selective detection of organic explosives

The detection of explosives is crucial for homeland security, environmental cleaning, and military issues. As a new class of porous materials, metal-organic frameworks (MOFs) are promising platforms for the detection of organic explosives. In this work, a new pillar-layered Cd(II) MOF, [CdL_0.5dpe_0.5]·2H₂O (BUT-202, H₄L = 4,8-disulfonaphthalene-2,6-dicarboxylic acid, dpe = 1,2-bis(4-pyridyl)ethylene), was synthesized and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and elemental analysis. BUT-202 has good fluorescent properties, which can be selectively quenched by trace amounts of 2,4,6-trinitrophenol (TNP) in DMF with low detection limit of 0.2 μM.     

Spider-web-like chitosan/MIL-68(Al) composite nanofibers for high-efficient solid phase extraction of Pb(II) and Cd(II)

Microchimica Acta - The authors describe the synthesis of spider-web-like chitosan/MIL-68(Al) composite nanofibers, their application to fast solid phase extraction (SPE) of trace levels...     

A metal-organic framework nanocomposite made from functionalized magnetite nanoparticles and HKUST-1 (MOF-199) for preconcentration of Cd(II), Pb(II), and Ni(II)

The author describes the preparation of a magnetic metal organic framework of type MOF-199 containing magnetite (Fe₃O₄) nanoparticles carrying covalently immobilized 4-(thiazolylazo) resorcinol (Fe₃O₄@TAR). This material is shown to represent a viable sorbent for separation and preconcentration of Cd(II), Pb(II), and Ni(II) ions. Box-Behnken design was applied to optimize the parameters affecting preconcentration. Following elution with 0.6 mol L^?1 EDTA, the ions were quantified by FAAS. The capacity of the sorbent ranged between 185 and 210 mg g^?1. The limits of detection are 0.15, 0.40, and 0.8 ng mL^?1 for Cd(II), Ni(II), and Pb(II) ions, respectively. The relative standard deviations are <8.5 %. The method was successfully applied to the rapid extraction of trace amounts of these ions from sea food and agri food.

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Graphical abstract (a) A schematic diagram of Fe₃O₄ functionalization by TAR (4-(thiazolylazo) resorcinol). (b) The schematic illustration of the magnetic metal organic framework-TAR nanocomposite. H₃BTC: benzene-1,3,5-tricarboxylic acid; TEA: triethylamine; 3-CPS: 3-chloropropyl triethoxysilane.

     

Highly porous Co(II)-salicylate metal-organic framework: synthesis, characterization and magnetic properties

A new porous Co(II)-salicylate metal-organic framework material has been synthesized hydrothermally through the reaction of Co(II) chloride with sodium salicylate under mild alkaline pH conditions. To get an idea about the structural aspect of the material from the powder X-ray diffraction (PXRD) pattern, MAUD program has been successfully utilized and the assigned peaks match very well with a new tetragonal phase (space group, P4mm) having the unit cell parameters: a = b = 12.957 (0.042) ?; c = 12.738 (0.019) ?; α = β = γ = 90°, V = 2138.73 ?(3). N(2) adsorption/desorption analyses suggested the material is highly porous in nature having high BET surface area and pore dimensions of 2.0-3.0 nm, which is within the range of small mesopores. Thermogravimetric analysis (TGA) revealed that the H(2)O molecules may be removed from the framework without collapsing the structure and the material is stable up to ca. 573 K. The material is characterized thoroughly by using different characterization tools such as TEM, SEM, UV-visible reflectance spectroscopy, FT IR spectroscopy and photoluminescence spectroscopy. X-Ray photoelectron spectroscopic (XPS) analysis was employed to understand the oxidation state of the cobalt atom and presence of other elements within the framework. The material shows interesting magnetic properties, where the magnetic moments monotonically increase with the decrease in temperature down to 9 K. Below 9 K there is a steep increase in magnetization on further lowering the temperature, thereby suggesting the onset of a long range ferromagnetic transition with ferromagnetic Curie temperature, T(C) = 8.5 K. Furthermore, the M-H curve at 2 K shows a clear hysteresis loop with a coercive field 150 Oe and remnant magnetization 0.8 μ(B)/f.u.     

Preconcentration of mercury(II) using a thiol-functionalized metal-organic framework nanocomposite as a sorbent

A novel type of porous metal-organic framework (MOF) was obtained from thiol-modified silica nanoparticles and the copper(II) complex of trimesic acid. It is shown that this nanocomposite is well suitable for the preconcentration of Hg(II) ions. The nanocomposite was characterized by Fourier transfer infrared spectroscopy, X-ray powder diffraction, energy-dispersive X-ray diffraction and scanning electron microscopy. The effects of pH value, sorption time, elution time, the volume and concentration of eluent were investigated. Equilibrium isotherms were studied, and four models were applied to analyze the equilibrium adsorption data. The results revealed that the adsorption process obeyed the Langmuir model. The maximum monolayer capacity and the Langmuir constant are 210 mg g^?1 and 0.273 L mg^?1, respectively. The new MOF-based nanocomposite is shown to be an efficient and selective sorbent for Hg(II). Under the optimal conditions, the limit of detection is 20 pg mL^?1 of Hg(II), and the relative standard deviation is <7.2 % (for n?=?3). The sorbent was successfully applied to the rapid extraction of Hg(II) ions from fish, sediment, and water samples.

Synthesis of magnetically modified mesoporous nanoparticles and their application in simultaneous determination of Pb(II), Cd(II) and Cu(II)

In this study, a novel adsorbent from a mesoporous family (MCM-41) coating with CoFe₂O₄ and piperazine was synthesized by a simple and easy route. Its application for simultaneous preconcentration of three heavy metals including lead, cadmium and copper in real samples followed by a flame atomic absorption spectroscopy was investigated. The central composite design was employed for investigating the most effective factors of pH, amount of adsorbent, the equilibrium time and their interactions. Under the optimum conditions, the detection limits for lead, cadmium and copper were 0.50, 0.30 and 0.25 μg L^?1, respectively, and the preconcentration factor (PF) was 33. The presented method was successfully employed for the simultaneous determination of the three mentioned heavy metals in real samples with recoveries of 90%–105%. The accuracy of the suggested methods was also investigated through spiking samples and a reasonable range for recoveries from 90.3% to 107% was acquired. The isotherm models and thermodynamic parameters have also been studied. The new adsorbent showed fast adsorption kinetics within 10 min and maximum Langmuir monolayer capacities of 238.09, 178.57 and 208.33 mg g^?1 for lead, cadmium and copper, respectively.     

Solid phase extraction of trace amounts of Pb(II) in opium, heroin, lipstick, plants and water samples using modified magnetite nanoparticles prior to its atomic absorption determination

A new, simple, fast and reliable solid-phase extraction method has been developed for separation/preconcentration of trace amounts of Pb(II) using dithizone/sodium dodecyl sulfate-immobilized on alumina-coated magnetite nanoparticles, and its determination by flame atomic absorption spectrometry (FAAS) and graphite furnace atomic absorption spectrometry (GFAAS) after eluting with 4.0?mol?L^?1 HNO₃. Optimal experimental conditions including pH, sample volume, eluent concentration and volume, and co-existing ions have been studied and established. Under the optimal experimental conditions, the preconcentration factor, detection limit, linear range and relative standard deviation of Pb(II) using FAAS technique were 280 (for 560?mL of sample solution), 0.28?ng?mL^?1, 1.4?C70?ng?mL^?1 and 4.6% (for 10?ng?mL^?1, n?=?10), respectively. These analytical parameters using GFAAS technique were 300 (for 600?mL of sample solution), 0.002?ng?mL^?1, 0.006?C13.2?ng?mL^?1 and 3.1% (for 5?ng?mL^?1, n?=?10), respectively. The presented procedure was successfully applied for determination of Pb(II) content in opium, heroin, lipstick, plants and water samples.     

Bismuth-dispersed xerogel-based composite films for trace Pb(II) and Cd(II) voltammetric determination

We report for the first time the synthesis of bismuth-modified (3-mercaptopropyl) trimethoxysilane (MPTMS) and its application for the determination of lead and cadmium by anodic stripping voltammetry. Xerogels made from bismuth-modified MPTMS and mixtures of it with tetraethoxysilane, under basic conditions (NH₃·H₂O), were characterized with scanning electron microscopy, energy dispersive spectroscopy, infrared spectroscopy and electrochemical methods. Bismuth-modified xerogels were mixed with 1.5% (v/v) Nafion in ethanol and applied on glassy carbon electrodes. During the electrolytic reductive deposition step, the bismuth compound on the electrode surface was reduced to metallic bismuth. The target metal cations were simultaneously reduced to the respective metals and were preconcentrated on the electrode surface by forming an alloy with bismuth. Then, an anodic voltammetric scan was applied in which the metals were oxidized and stripped back into the solution; the voltammogram was recorded and the stripping peak heights were related to the concentration of Cd(II) and Pb(II) ions in the sample. Various key parameters were investigated in detail and optimized. The effect of potential interferences was also examined. Under optimum conditions and for preconcentration period of 4 min, the 3σ limit of detection was 1.3 μg L⁻¹ for Pb(II) and 0.37 μg L⁻¹ for Cd(II), while the reproducibility of the method was 4.2% for lead (n = 5, 10.36 μg L⁻¹ Pb(II)) and 3.9% for cadmium (n = 5, 5.62 μg L⁻¹ Cd(II)). Finally, the sensors were applied to the determination of Cd(II) and Pb(II) ions in water samples.     

Cd(II) and Pb(II) extraction and transport modeling in SLM and PIM systems using Kelex 100 as carrier

The extraction and transport of Cd(II) and Pb(II) in two different membrane systems (SLM and PIM) using Kelex 100 as carrier was studied, proposing the corresponding chemical models of transport. A two-species transport model is proposed for Cd(II), according to solvent extraction (SX) data. Experimental SLM permeabilities are 9.7×10⁻⁵ m s⁻¹, while measured PIM permeabilities are 5×10⁻⁵ m s⁻¹. Values for the aqueous boundary layer thickness and for the diffusion coefficient of the metal cation-carrier complexes in the membrane phase were calculated from numerical fitting of experimental data using the proposed transport models. A highly selective Pb(II) separation was achieved in PIM systems based on the nature of the chemical equilibria involved in Cd(II) and Pb(II) membrane transport.     

Preconcentration of Cd(II), Pb(II), Co(II), Ni(II), and Cu(II) by solid-phase extraction method using 1,10-phenanthroline

Solid-phase extraction (SPE) method for preconcentration and determination of Cd(II), Pb(II), Co(II), Ni(II), and Cu(II) aqueous samples by inductively coupled plasma optical emission spectrometry is described. The preconcentration of analytes is accomplished by retention of their chelates with 1.10-phenanthroline in aqueous solution on a solid phase containing carboxylic acid (COOH) bonded to silica gel in a column. The limits of detection values (defined as “3s” where “s” is standard deviation of the blank determination) are 3.6 μg/L for Cd(II), 17.5 μg/L for Pb(II), 3.1 μg/L for Co(II), 2.1 μg/L for Ni(II), and 4.4 μg/L for Cu(II) and corresponding limit of quantification (6s) values are 7.2, 35, 6.2, 4.2 and 8.8 μg/L, respectively. As a result, a simple method was elaborated for the group concentration and determination of the above mentioned metals in reference material and in samples of plant material. The article is published in the original.     

Solid phase extraction of lead (II), copper (II), cadmium (II) and nickel (II) using gallic acid-modified silica gel prior to determination by flame atomic absorption spectrometry

The immobilization of gallic acid on the surface of amino group-containing silica gel phases for the formation of a newly chelating matrix (GASG) is described. The newly synthesized extractant, characterized by the diffuse reflectance infrared Fourier transformation spectroscopy and elemental analysis, was used to preconcentrate Pb(II), Cu(II), Cd(II) and Ni(II). The pH ranges for quantitative sorption and the concentrations of HCl for eluting Pb(II), Cd(II), Cu(II) and Ni(II) were opimized, respectively. The sorption capacity of the matrix has been found to be 12.63, 6.09, 15.38, 4.62mg/g for Pb(II), Cd(II), Cu(II) and Ni(II), respectively, with the preconcentration factor of approximately 200 ( approximately 100 for Cd(II)). The effects of flow rates, the eluants, the electrolytes and cations on the metal ions extraction, as well as the chelating matrix stability and reusability, were also studied. The extraction behavior of the matrix was conformed with Langmuir's equation. The present preconcentration and determination method was successfully applied to the analysis of synthetic metal mixture solution and river water samples. The 3sigma detection limit and 10sigma quantification limit for Pb(II), Cu(II), Cd(II) and Ni(II) were found to be 0.58, 0.86, 0.65, 0.92microg/L and 1.08, 1.23, 0.87, 1.26microg/L, respectively.