Nanometer titanium dioxide immobilized on silica gel as sorbent for preconcentration of metal ions prior to their determination by inductively coupled plasma atomic emission spectrometry

Nanometer titanium dioxide immobilized on silica gel (immobilized nanometer TiO₂) was prepared by sol-gel method and characterized by using X-ray diffraction (XRD) and scanning electron microscope (SEM). The adsorptive potential of immobilized nanometer TiO₂ for the preconcentration of trace Cd, Cr, Cu and Mn was assessed in this work. The metal ions studied can be quantitative retained at a pH range of 8-9, and 0.5 mol L⁻¹ HNO₃ was sufficient for complete elution. The adsorption capacity of immobilized nanometer TiO₂ for Cd, Cr, Cu and Mn was found to be 2.93, 2.11, 6.69 and 2.47 mg g⁻¹, respectively. A new method using a microcolumn packed with immobilized nanometer TiO₂ as sorbent has been developed for the preconcentration of trace amounts of Cd, Cr, Cu and Mn prior to their determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). The method has been successfully applied for the determination of trace elements in some environmental samples with satisfactory results.     

ICP-AES determination of trace elements after preconcentrated with p-dimethylaminobenzaldehyde-modified nanometer SiO2 from sample solution

A new method that utilizes p-dimethylaminobenzaldehyde-modified nanometer SiO₂ (SiO₂-p-DMABD) 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). The preconcentration conditions of analytes were investigated, including the pH value, the shaking time, the mass of sorbent, the sample flow rate and volume, the elution condition and the interfering ions. The adsorption capacity of nanometer SiO₂-p-DMABD was found to be (mg g^− 1) Cr(III): 6.2, Cu(II): 18.6, Fe(III): 4.7 and Pb(II): 6.0 at pH 4. The adsorbed metals were quantitatively eluted with 4 mL of 1.0 mol L^− 1 HCl. According to the definition of IUPAC, the detection limits (3σ) of this method for Cr(III), Cu(II), Fe(III) and Pb(II) were 0.79, 1.27, 0.40 and 1.79 ng mL^− 1, respectively. The proposed method achieved satisfied results when it was applied to the determination of trace Cr(III), Cu(II), Fe(III) and Pb(II) in biological and water samples.     

Highly sensitive spectrofluorimetric determination of cysteine by Cu2+-morin complex

p-Toluenesulfonylamide was immobilized on silica gel and on nm-sized silicium dioxide (SiO₂). Their adsorption efficiency toward metal ions was investigated by the batch equilibrium technique. Although silica gel and nm-SiO₂ have the same composition (silicon and oxygen), the difference in their sizes and surface structures results in distinct chemical activity and selectivity. At pH 4, the adsorption capacity of modified silica gel adsorbent was found to be 4.9, 5.0, 33.2, and 12.6 mg g⁻¹ for Cr(III), Cu(II), Pb(II) and Zn(II), respectively. However, the adsorption capacity of nm-SiO₂ adsorbent toward Cr(III) was 26.7 mg g⁻¹ under ultrasonic dispersing. The potential application of p-toluenesulfonylamide-modified silica gel for simultaneous preconcentration of trace chromium, copper, lead and zinc from two standard reference materials and two food samples was performed with satisfactory results. Correspondence: Xijun Chang, Department of Chemistry, Lanzhou University, Lanzhou 730000, P.R. China     

Micro-column preconcentration/separation using thiacalix[4]arene tetracarboxylate derivative modified mesoporous TiO2 as packing materials on-line coupled to inductively coupled plasma optical emission spectrometry for the determination of trace heavy metals in environmental water samples

A novel adsorbent of thiacalix[4]arene tetracarboxylate derivative modified mesoporous TiO₂ was prepared and was used as a packing material for flow injection (FI) micro-column (20 mm × 4.0 mm i.d.) separation/preconcentration on-line coupled to inductively coupled plasma optical emission spectrometry (ICP-OES) simultaneous determination of trace metals (V, Cu, Pb, Cr) in environmental water samples. The experimental conditions for modified mesoporous TiO₂ packed micro-column separation/preconcentration of the target metals were optimized and the interference of commonly coexisting ions was examined. The adsorption capacities of thiacalix[4]arene tetracarboxylate derivative modified mesoporous TiO₂ for V, Cu, Pb and Cr were found to be 14.0, 11.7, 17.7 and 14.5 mg g^− 1, respectively. The detection limits of the method were 0.09, 0.23, 0.50 and 0.15 µg L^− 1 for V, Cu, Pb and Cr, respectively, with a preconcentration factor of 20. The precision of this method were 1.7% (V), 3.9% (Cu), 4.6% (Pb) and 2.9% (Cr) (n = 7, C = 5 µg L^− 1), respectively. The developed method was applied to the determination of trace heavy metals in real samples and the recoveries for spiked samples were found to be in the range of 88.7-107.1%. For validation, a certified reference material of GSBZ50009-88 environmental water sample was analyzed and the determined values were in good agreement with the certified values.     

Selective solid-phase extraction of trace Fe(III) from biological and natural water samples using nanometer SiO2 modified with acetylsalicylic acid

A new method using acetylsalicylic acid (aspirin) modified SiO₂ nanoparticles (nanometer SiO₂-aspirin) as a solid-phase extractant (SPE) has been developed for the preconcentration of trace amounts of Fe(III) prior to their determination by inductively coupled plasma optical emission spectrometry. The preconcentration conditions of analytes were investigated, including the pH value, the shaking time, the mass of sorbent, the sample flow rate and volume, the elution condition and the interfering ions. At pH 4, the sorption capacity of nanometer SiO₂-aspirin was found to be 1.28 mmol g⁻¹. The preconcentration factor is 50. The detection limit (3σ) for Fe(III) was 0.49 ng mL⁻¹. The method was validated by analyzing two certified reference materials (GBW 08301, river sediment and GBW 08303, polluted farming soil), and the results obtained are in good agreement with standard values. The method was also applied to the determination of trace Fe(III) in biological and water samples with satisfactory results. Correspondence: Xiangbing Zhu, Department of Chemistry, Lanzhou University, Lanzhou 730000, P.R. China     

Speciation analysis of selenoproteins in human serum by microbore affinity-HPLC hyphenated to ICP-Sector field-MS using a high efficiency sample introduction system

Silica gel and nanometer SiO₂ modified with 4-(2-aminoethylamino)-N-(2-(2-aminoethyl amino)ethyl)butanamide (SG-AAEB and nanometer SiO₂-AAEB), which were prepared based on chemical immobilization, were used as sorbents for the solid phase extraction of Cu(II), Fe(III), and Pb(II) prior to their determination by inductively coupled plasma optical emission spectrometry. Adsorption efficiencies of the two sorbents towards metal ions were investigated by batch and column procedures. For both sorbents the preconcentration conditions of analytes including effects of pH, shaking time, sample flow rate and adsorption capacity, were investigated and compared. The differences of silica gel and nanometer SiO₂ in sizes and surface structures resulted in distinct chemical activity and selectivity toward metals. At pH 4, the adsorption capacity of SG-AAEB was found to be 12.2, 14.5 and 9.8 mg g^?1 for Cu(II), Fe(III), and Pb(II), respectively. In comparison, nanometer SiO₂-AAEB showed a high selectivity toward Pb(II) and has a much larger adsorption capacity (22.3 mg g^?1). Furthermore, the application of SG-AAEB and nanometer SiO₂-AAEB for simultaneous preconcentration of trace Cu(II), Fe(III), and Pb(II) from natural samples was performed with satisfactory results.     

A pre-enrichment procedure using diethyldithiocarbamate-modified TiO2 nanoparticles for the analysis of biological and natural water samples by ICP-AES

In this article, a new method that utilizes a diethyldithiocarbamate-modified nanometre TiO₂ (TiO₂–DDTC) as solid-phase extractant has been developed for simultaneous preconcentration of trace Cu(II), Pb(II), Zn(II), and Cd(II) prior to measurement by inductively coupled plasma atomic emission spectrometry (ICP-AES). The separation/preconcentration conditions of analytes, which include the effects of pH, sample flow rate and volume, elution conditions, and interfering ions on the recovery of the analytes, were investigated. At pH 5, the adsorption capacity of modified nanometre TiO₂–DDTC was found to be 6.2, 19, 4.7, and 6.0?mg/g for Cu(II), Pb(II), Zn(II), and Cd(II), respectively. According to the definition of IUPAC, the detection limits (3σ) of this method for Cu(II), Pb(II), Zn(II), and Cd(II) were 0.41, 1.7, 0.39, and 0.52?ng/mL, respectively. The proposed method achieved satisfied results when applied to the determinations of trace Cu(II), Pb(II), Zn(II), and Cd(II) in biological and natural water samples.     

Determination of Lead, Chromium, Manganese and Zinc in Slurries of Botanical and Biological Samples by Electrothermal Atomic Absorption Spectrometry Using Tungsten-Containing Chemical Modifiers

Lead, Cr, Mn and Zn in slurries of botanic and biological samples were determined by electrothermal atomic absorption spectrometry (ETAAS) using W, Ir, NH₄H₂PO₄, W and NH₄H₂PO₄, Ir and NH₄H₂PO₄, W and Ir, and W + Ir + NH₄H₂PO₄ chemical modifiers in an 0.2% (v/v) Triton X-100 plus 0.2% (v/v) nitric acid mixture. Zeeman effect background correction was performed and platforms inserted into graphite tubes were used. Comprehensive comparative studies were carried out with respect to pyrolysis and atomization temperatures, atomization and background absorption profiles, characteristic masses, detection limits and accuracy of the determinations in the presence and absence of modifiers. The mixture of W + Ir + NH₄H₂PO₄ was found to be preferable for the determination of Pb, Cr, Mn and Zn in slurry samples. The pyrolysis temperatures of the analytes were increased up to 1250 °C for Pb, 1000 °C for Zn, 1400 °C for Cr and Mn by using W + Ir + NH₄H₂PO₄ with an 0.2% (v/v) Triton X-100 plus 0.2% (v/v) nitric acid mixture used as diluent solution. The optimum masses of the mixed modifier components were found to be 20 µg W + 4 µg Ir + 50 µg NH₄H₂PO₄. The characteristic masses of Pb, Cr, Mn and Zn obtained are 16.3, 5.6, 0.1 and 1.1 pg, respectively. The detection limits of Pb, Cr, Mn and Zn based on integrated absorbance for 0.5% (m v⁻¹) slurries were found to be 0.14, 0.06, 0.02 and 0.01 µg g⁻¹, respectively. The slurries of botanic and biological certified and standard reference materials were analyzed with and without the modifiers. Depending on the sample type, the percent recoveries increased from 63 up to 104% for analytes when using the proposed modifier mixture.     

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.     

Determination of Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb in natural waters, alkali and alkaline earth salts by electrothermal atomic absorption spectrometry after preconcentration by column solid phase extraction

Methods are described for the determination of trace and ultra trace amounts of Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb in natural waters, alkali and alkaline earth salts. Separation and preconcentration of trace metals is achieved by a column solid phase extraction procedure using silica gel modified with derivatives of dithiocarbamates — Na-DDTC (sodium diethyldithio-carbamate and HMDTC (ammonium hexamethylene-dithiocarbamate) as column packing material. The influence of the sorbent preparation procedure on the degree of sorption of the trace analytes is examined for different pH values of the sample solution. Isobutylmethyl ketone (IBMK) is proposed as an effective eluent for quantitative elution of retained metal ions. Optimal instrumental parameters for ETAAS determination of preconcentrated elements in organic eluate are presented. Practical application of sorbents in analysis of natural waters and alkali and alkaline earth salts is demonstrated. Proposed preconcentration procedure combined with ETAAS determination of trace analytes allows the determination of 0.04 g l^–1 Cd, 0.1 g l^–1 Cr, Cu, and Mn and 0.3 g l^–1 Co, Fe, Ni and Pb in natural waters and 1.10^–7% Cd, 3.10^–7% Cr and Mn, 7.10^–7% Co, Ni and Pb and 2.10^–6% Cu and Fe in alkali and alkaline earth salts.     

Determination of gold by nanometer titanium dioxide immobilized on silica gel packed microcolumn and flame atomic absorption spectrometry in geological and water samples

A new method has been developed for the determination of gold based on separation and preconcentration with a microcolumn packed with nanometer TiO₂ immobilized on silica gel (immobilized nanometer TiO₂) prior to its determination by flame atomic absorption spectrometry. The optimum experimental parameters for preconcentration of gold, such as pH of the sample, sample flow rate and volume, eluent and interfering ions, have been investigated. Gold could be quantitatively retained by immobilized nanometer TiO₂ in the pH range of 8-10, then eluted completely with 0.1 mol L⁻¹ HNO₃. The detection limit of this method for Au was 0.21 ng mL⁻¹ with an enrichment factor of 50, and the relative standard deviation (R.S.D.) was 1.8% at the 100 ng mL⁻¹ Au level. The method has been applied for the determination of trace amounts of Au in geological and water samples with satisfactory results.     

Nanometer-sized zirconium dioxide microcolumn separation/preconcentration of trace metals and their determination by ICP-OES in environmental and biological samples

A new method is proposed using a microcolumn (20 mm × 2.0 mm) packed with nanometer-sized zirconia as solid-phase extractor for the separation/preconcentration of Mn, Cu, Cr, Zn, Ni and Co prior to their determination by inductively coupled plasma optical emission spectrometer (ICP-OES) in environmental samples. The factors affecting the separation and preconcentration of analytes such as pH, sample flow rate and volume, eluent concentration and volume were determined, interfering ions were studied, and the optimal experimental conditions were established. The adsorption capacity of nanometer-sized ZrO₂ for Mn, Cu, Cr, Zn, Ni and Co was found to be 1.3, 1.3, 1.7, 2.0, 3.9 and 1.5 mg g⁻¹, respectively. The detection limits of the method were 12, 58, 24, 2, 7 and 36 ng L⁻¹, respectively, with a preconcentration factor of 25. The precision of this method was 1.7% (Mn), 2.9% (Cu), 5.9% (Mn), 3.8% (Mn), 6.2% (Mn) and 4.3% (Mn) with 9 determinations of 10 ng mL⁻¹ of target analytes, respectively. The method was successfully applied to the determination of trace metals in lake water, dried fish samples, certified reference materials of human hair and milk, and provided satisfactory results.     

Determination of trace elements in AR grade alkali salts after preconcentration by column solid-phase extraction on TiO2 (anatase)

 Column solid-phase extraction using TiO₂ (anatase) as a solid sorbent was applied to preconcentrate traces of Cd, Co, Cu, Fe, Mn, Ni and Pb from AR grade alkali salts prior to their measurements by atomic absorption spectrometry (AAS). Multi-element preconcentration was achieved from NaCl, KCl, KNO₃, NaNO₃, CH₃COONa, NaHCO₃ and Na₂CO₃ solutions, whereas the sorption of trace elements from phosphates and sulfates is not quantitative. Optimal conditions (recoveries of the analytes >95%) for solid-phase co-extraction of the most common heavy metal ions are proposed. The conditions for quantitative and reproducible elution and subsequent AAS are established. A method of determination of trace elements in different salts is proposed. It is characterized by precision, reproducibility and a high preconcentration factor. The solid-phase extraction by TiO₂, combined with ETAAS allows the determination of 0.1 ng g^-1 Cd, 2 ng g^-1 Co, 1 ng g^-1 Cu and Ni, 0.5 ng g^-1 Mn and 0.4 ng g^-1 Pb. Received: 1 April 1996/Revised: 24 June 1996/Accepted: 9 July 1996     

Solid phase extraction and flame atomic absorption spectrometric determination of trace amounts of cadmium and lead in water and biological samples using modified TiO2 nanoparticles

A solid phase extraction procedure for the separation and preconcentration of trace amounts of Cd(II) and Pb(II) using the alizarin red S modified TiO₂ nanoparticles prior to their determination by flame atomic absorption spectrometry has been proposed. The influences of some analytical parameters such as pH, flow rates of sample and eluent, type and concentration of the eluent, and interfering ions on the recovery of Cd(II) and Pb(II) by the sorbent were investigated. The analytes were quantitatively sorbed from the aqueous solution at pH 5.5 onto a microcolumn packed with the sorbent and recovered with 2.0?mL of 1.5?mol?L^?1 hydrochloric acid. Under the optimum experimental conditions, the detection limits for Cd(II) and Pb(II) were 0.11 and 0.30?ng?mL^?1 and the relative standard deviations for ten replicate measurements of 5.0 and 50.0?ng?mL^?1 of Cd(II) and Pb(II) were 2.1 and 1.9%, respectively. A sample volume of 200?mL resulted in a preconcentration factor of 100. The method was successfully applied to the determination of Cd(II) and Pb(II) in water and biological samples, and accuracy was examined by the recovery experiments, independent analysis using electrothermal atomic absorption spectrometry, and analysis of a water standard reference material (SRM 1643e).     

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.     

Use of modified rice husks as a natural solid adsorbent of trace metals: characterisation and development of an on-line preconcentration system for cadmium and lead determination by FAAS

The use of rice husks as an alternative adsorbent in an on-line preconcentration system for Cd (II) and Pb (II) determination by flame atomic absorption spectrometry (FAAS) is described. The potential of rice husks as a natural adsorbent was evaluated as a material modified with 0.75 mol l⁻¹ NaOH solution and in the unmodified form. For this task, several techniques such as spectroscopy and thermogravimetry were used for elucidation of possible functional groups responsible for the uptake of Cd (II) and Pb (II). Furthermore, based on adsorption studies and adsorption isotherms applied to the Langmüir model, it was possible to verify that modified rice husks present a higher adsorption capacity for both metals. After establishing this material as a promising natural adsorbent, it was used for on-line preconcentration of Cd (II) and Pb (II) metals. The multivariate optimisation of chemical and flow variables was performed by using a full factorial design (2⁴) including the following factors: preconcentration time, preconcentration flow rate, concentration and volume of eluent. The optimum pH values used for on-line preconcentration were taken from prior univariate experiments. Under optimised conditions for Cd (II) determination (4 min of preconcentration at a 6 ml min⁻¹ preconcentration flow rate, in which comprises 24 ml of preconcentration volume, 200 μl elution volume and 1.0 mol l⁻¹ HNO₃ solution as eluent), the system achieved a detection limit of 1.14 μg l⁻¹ and an enrichment factor of 72.4. Similar conditions were used for Pb (II) determination (4 min of preconcentration, 6 ml min⁻¹ preconcentration flow rate, 300 μl elution volume and 1.0 mol l⁻¹ HNO₃ solution as eluent) from which a detection limit of 14.1 μg l⁻¹ and enrichment factor of 46.0 were achieved. Also, rice husks have been shown to be a homogeneous and stable adsorbent in which more than 100 preconcentration/elution cycles provide a relative standard deviation (RSD) of less than 6.0% on the analytical signal. The satisfactory accuracy of the method developed was obtained by using spiked water samples (mineral water and lake water) and spiked red wine samples. These values were confirmed by electrothermal atomic absorption spectrometry (ETAAS). The certified reference material [pig kidney (CRM 186)] and the reference material [beech leaves (CRM 100)] were also used.     

Determination of trace elements in pharmaceutical substances by graphite furnace atomic absorption spectrometry and total reflection X-ray fluorescence after flow injection ion-exchange preconcentration

Flow injection iminodiacetic acid ethyl cellulose (IDAEC) microcolumn preconcentration and graphite furnace atomic absorption spectrometry determination of trace metals (Cd, Co, Ni, Pb) were carried out without decomposition of the drug matrix. The two forms of chromium Cr(III) and Cr(VI) were separated using IDAEC and anion exchanger diethylaminoethyl (DE)-cellulose, respectively. The detection limits of trace elements in pharmaceutical substances (sugars, sorbitol, mannitol, paracetamol, amidopyrine, chloral hydrate) after a 10-fold preconcentration in 1–5% m/v solution of pharmaceuticals were in the 0.3–29 ng g⁻¹ range. The measured concentration of trace elements in substances investigated was below 100 ng g⁻¹. The spike recovery was close to 100%. The capability of total reflection X-ray fluorescence technique for the determination of trace elements in pharmaceuticals with and without preconcentation was explored.     

Speciation analysis of chromium in natural water samples by electrothermal atomic absorbance spectrometry after separation/preconcentration with nanometer-sized zirconium oxide immobilized on silica gel

Silica gel was prepared by the sol–gel method, modified with nanometer-sized zirconium oxide, and this material was characterized by X-ray diffraction. A micro-column packed with silica gel modified with nanometer zirconium oxide as sorbent has been developed for the quantitative separation and preconcentration of trace amounts of chromium(III) prior to their determination by electrothermal atomic absorption spectrometry. Total chromium was determined after the reduction of chromium(VI) to chromium(III) by 10% (m/v) of aqueous ascorbic acid as reducing reagent. The adsorption capacity for chromium(III) was found to be 2.36 mg g⁻¹. The detection limit for chromium(III) was 15 ng L⁻¹ with an enrichment factor of 100. The relative standard deviation was 3.2% (n = 7, c = 2.0 ng mL⁻¹).     

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.     

Preparation of morin modified nanometer SiO<Subscript>2</Subscript> as a sorbent for solid-phase extraction of trace heavy metals from biological and natural water samples

Morin was successful as a chemical modifier to improve the reactivity of the nanometer SiO₂ surface in terms of selective binding and extraction of heavy metal ions. This new functionalized nanometer SiO₂ (nanometer SiO₂-morin) was used as an effective sorbent for the solid-phase extraction (SPE) of Cd(II), Cu(II), Ni(II), Pb(II), Zn(II) in solutions prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Experimental conditions for effective adsorption of trace levels of metal ions were optimized with respect to different experimental parameters using static and dynamic procedures in detail. The pH 4.0 was chosen as the optimum pH value for the separation of metal ions on the newly sorbent. Complete elution of the adsorbed metal ions from the nanometer SiO₂-morin was carried out using 2.0 mL of 0.5 mol L⁻¹ of HCl. Common coexisting ions did not interfere with the separation and determination at pH 4.0. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 22.36, 36.8, 40.37, 33.21 and 25.99 mg metal/g SiO₂-morin for Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II), respectively. The time for 95% sorption for Cu(II) and Ni(II) and 70% sorption for Cd(II), Pb(II) and Zn(II) was less than 2 min. The relative standard deviation (RSD) of the method under optimum conditions was lower than 5.0% (n = 11). The procedure was validated by analyzing the certified reference river sediment material (GBW 08301, China), the results obtained were in good agreement with standard values. The nanometer SiO₂-morin was successfully employed in the separation and preconcentration of trace Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II) from the biological and natural water samples yielding 75-folds concentration factor.