Development of urease based amperometric biosensors for the inhibitive determination of Hg (II)

Enzymatic amperometric procedures for measurement of Hg (II), based on the inhibitive action of this metal on urease enzyme activity, were developed. Screen-printed carbon electrodes (SPCEs) and gold nanoparticles modified screen-printed carbon electrodes (AuNPs/SPCEs) were used as supports for the cross-linking inmobilization of the enzyme urease. The amperometric response of urea was affected by the presence of Hg (II) ions which caused a decreasing in the current intensity. The optimum working conditions were found using experimental design methodology. Under these conditions, repeatability and reproducibility for both types of biosensors were determined, reaching values below 6% in terms of residual standard deviation. The detection limit obtained for Hg (II) was 4.2 × 10^?6 M for urease/SPCE biosensor and 5.6 × 10^?8 M for urease/AuNPs/SPCE biosensor. Analysis of the possible effect of the presence of foreign ions in the solution was performed. The method was applied to determine levels of Hg (II) in spiked human plasma samples.     

Urease–glutamic dehydrogenase biosensor for screening heavy metals in water and soil samples

A screen-printed three-electrode amperometric biosensor based on urease and the nicotinamide adenine dinucleotide hydrogen (NADH)–glutamic dehydrogenase system was developed and applied to the screening of heavy metals in environmental samples. The development of an amperometric sensor for the monitoring of urease activity was feasible by coupling the urea breakdown reaction catalysed by urease to the reductive ammination of ketoglutarate catalysed by glutamic dehydrogenase (GLDH). The ammonia provided by the urea conversion is required for the conversion of ketoglutarate to glutamate with the concomitant oxidation of the NADH cofactor. NADH oxidation is monitored amperometrically at 0.3 V (vs. Ag/AgCl) after urease immobilization onto the screen-printed three-electrode configuration. Immobilization of urease on the surface of screen-printed electrodes was performed by entrapment in alginate gel and adsorption on the electrode in a nafion film. Low sensitivity to inactivation by metals was recorded after urease entrapment in alginate gel with detection limits of 2.9 and 29.8 mg L^–1 for Hg(II) and Cu(II), respectively. The use of the negatively charged nafion film created a more concentrated environment of cations in proximity to the enzyme, thus enhancing the urease inhibition when compared to gel entrapment. The calculated detection limits were 63.6 and 55.3 g L^–1 for Hg(II) and Cu(II), respectively, and 4.3 mg L^–1 for Cd(II). A significant urease inactivation was recorded in the presence of trace amounts of metals (g L^–1) when the enzyme was used free in solution. Analysis of water and soil samples with the developed nafion-based sensor produced inhibition on urease activity according to their metal contents. The obtained results were in agreement with the standard methods employed for sample analysis. Nevertheless, the use of the amperometric assay (with free urease) proved more feasible for the screening of trace amounts of metals in polluted samples.     

Dye-ligand immobilized IPNs membrane for removal heavy metal ions

We have developed a novel approach to obtain high metal sorption capacity utilizing a membrane containing chitosan and an immobilized reactive dye (i.e. Reactive Yellow-2). The composite membrane was characterized by SEM, FT-IR, swelling test, and elemental analysis. The membrane has uniform small pores distribution and the pore dimensions are between 5 and 10 μm, and the HEMA:chitosan ratio was 50:1. The reactive dye immobilized composite membrane was used in the removal of heavy metal ions [i.e., Pb(II), Hg(II) and Cd(II)] from aqueous medium containing different amounts of these ions (5-600 mg l⁻¹) and at different pH values (2.0-7.0). The maximum adsorption capacities of heavy metal ions onto the composite membrane under non-competitive conditions were 64.3 mmol m⁻² for Pb(II), 52.7 mmol m⁻² for Hg(II), 39.6 mmol m⁻² for Cd(II) and the affinity order was Pb(II) > Hg(II)>Cd(II).     

A metal organic framework prepared from benzene-1,3,5-tricarboxylic acid and copper(II), and functionalized with various polysulfides as a sorbent for selective sorption of trace amounts of heavy metal ions

Novel composites were obtained via direct assembly of polysulfides (S_x^2?, X?=?3, 4, 6) on the surface of a metal organic framework (MOF; type benzene-1,3,5-tricarboxylic/Cu(II). They are referred to as S_x-MOFs and were used for highly selective and efficient extraction of ultra-trace amounts of heavy metal ions from aqueous solutions. The structure of the S_x-MOFs was characterized by Raman spectroscopy, FT-IR, X-ray diffraction, and scanning electron microscopy. The Raman spectra of S_x-MOF is similar to the bare MOF and shows the MOFs structure to be well retained after S_x functionalization. The selective interaction of S_x with soft metal ions and the high surface area of MOFs resulted in excellent affinity and selectivity for ions such as Hg(II). The S_x-MOFs of type S₄-MOF had the highest distribution coefficient K_d value (~10⁷) and best extraction recovery (~100%) for Hg(II). The S₄-MOF also has high selectivity in the following order: Hg(II) >?>?Pb(II)?>?Zn(II)?>?Ni(II)?>?Co(II). The binding process of the metals occurs via M–S bonding. The ions were quantified by inductively coupled plasma optical emission spectrometry (ICP-OES). The detection limit for Hg(II) is 0.13 μg L^?1. The S₄-MOF was applied to the extraction of trace metal ions from natural and contaminated waters and data were compared with other sorbets. The results revealed that S₄-MOF is an excellent adsorbent for sorption of heavy metal ions even in the presence of the relatively high concentration of other ions.

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Graphical abstract A composite was synthesized via direct assembly of polysulfides (S_x^2?, X?=?3, 4, 6) on surface of the metal organic framework (S_x-MOF) and was used for selective and efficient extraction of ultra-trace amounts of heavy metal ions from aqueous solutions.

     

Sol-gel derived urease-based optical biosensor for the rapid determination of heavy metals

A urease optical biosensor for the determination of heavy metals based on sol-gel immobilization technique was developed. A fluorescent dye, FITC-dextran, was encapsulated and parameters including optical properties of the probe, relative enzyme activity, initial pH value and the buffer concentration for substrate preparation were investigated. In sol-gel immobilization, 1 mM Tris-HCl at pH 7.1 provided a sufficient buffer capacity for metal ion analysis as well as the enzyme activity maintenance. Also, two analytical procedures, incubated and un-incubated systems, were compared to understand the sensitivity and applicability to heavy metal analysis. The developed optical biosensor showed high reproducibility and the relative standard deviation (R.S.D.) of 5.1% (n=10) was obtained. Also, eight measurements can be completed automatically within 36 min. The biosensor has high sensitivity to Cu(II) and Cd(II) and an analytical range of 10-230 μM with a detection limit of 10 μM was achieved. Moreover, biological and environmental samples were examined to evaluate the applicability of the developed biosensor. A 19-82% of inhibition was observed when 20-45 μM metal ions were amended into tested samples, revealing that the developed system has the potential for the determination of heavy metals in real samples.     

Highly selectively monitoring heavy and transition metal ions by a fluorescent sensor based on dipeptide

Fluorescent sensor (DMH) based on dipeptide was efficiently synthesized in solid phase synthesis. The dipeptide sensor shows sensitive response to Ag(I), Hg(II), and Cu(II) among 14 metal ions in 100% aqueous solution. The fluorescent sensor differentiates three heavy metal ions by response type; turn on response to Ag(I), ratiometric response to Hg(II), and turn off detection of Cu(II). The detection limits of the sensor for Ag(I) and Cu(II) were much lower than the EPA's drinking water maximum contaminant levels (MCL). Specially, DMH penetrated live cells and detected intracellular Ag⁺ by turn on response. We described the fluorescent change, binding affinity, detection limit for the metal ions. The study of a heavy metal-responsive sensor based on dipeptide demonstrates its potential utility in the environment field.     

Determination of mercury(II) traces in drinking water by inhibition of an urease reactor in a flow injection analysis (FIA) system

 The integration of an urease reactor into a gas diffusion flow injection system was investigated for the determination of urease inhibitors. The enzyme was immobilized by entrapping in polyacrylamide gel. Besides copper and silver ions mercury ions inhibit the conversion of urea to carbon dioxide and ammonia catalysed by urease. The pH change of the carrier solution caused by the ammonia released was measured potentiometrically with a pH electrode. The inhibition behaviour of Hg(II) ions was investigated. A linear range from 2 to 20 μg L^-1 Hg(II) was obtained after a 90 s inhibition, with a correlation coefficient of r=0.9997. The relative standard deviation was 1.4% for five measurements of 2 μg L^-1Hg(II). A sample frequency of 7 h^-1 was achieved. The inhibited enzyme can be reactivated. The method was applied to the determination of Hg(II) in two drinking water samples. Received: 16 April 1996/Revised: 3 June 1996/Accepted: 11 June 1996     

Determination of mercury(II) by surface-enhanced Raman scattering spectroscopy based on thiol-functionalized silver nanoparticles

Silver nanoparticles (Ag NPs) modified with sodium 2-mercaptoethanesulfonate (mesna) exhibit strong surface-enhanced Raman scattering (SERS). Their specific and strong interaction with heavy metal ions led to a label-free assay for Hg(II). The covalent bond formed between mercury and sulfur is stronger than the one between silver and sulfur and thus prevents the adsorption of mesna on the surface of Ag NPs. This results in a decrease of the intensity of SERS in the presence of Hg(II) ions. The Raman peak at 795?cm^?1 can be used for quantification. The effect of the concentration of mesna, the concentration of sodium chloride, incubation time and pH value on SERS were optimized. Under the optimal conditions, the intensity of SERS decreases with increasing concentration of Hg(II). The decrease is linear in the 0.01 and 2?μmol L^?1 concentration range, with a correlation coefficient (R²) of 0.996 and detection limit (S/N?=?3) is 0.0024?μmol L^?1. The method was successfully applied to the determination of the Hg(II) in spiked water samples.

‘Green’ immunochromatographic electrochemical biosensor for mercury(II)

We describe an immunochromatographic electrochemical biosensor (IEB) for highly specific and sensitive determination of Hg(II) ions. The IEB is based on the use of a new monoclonal antibody (McAb) against Hg(II) ions that affects the recognition of an antigen. The McAb is placed on the surface of gold nanoparticles (AuNPs) and can recognize the antigen only in the absence of Hg(II) ions. This detection scheme was used to design an immunochromatographic test strip using dually labeled AuNPs along with electrochemical detection. Signal amplification was accomplished by a competitive reaction and the use of horseradish peroxidase. Following immunochromatography, the test zone was cut out and transferred into a reaction cell loaded with a substrate solution containing ortho-phenylenediamine and H₂O₂. After 10-min incubation with horseradish peroxidase, square wave voltammetry was performed with a screen-printed electrode. Under optimal conditions and a working voltage of ?0.57 V, the IEB displays a linear response in the 0.1 to 200 ng.mL^?1 Hg(II) concentration range and a 30 pg.mL^?1 limit of detection. It was applied to the determination of Hg(II) in (spiked) waters and milk where its sensitivity by far surpassed the maximum allowed contamination levels. This sensitive IEB therefore possesses substantial advantages over other assays. In addition, the detection scheme may be extended to other metal ions for which appropriate antibodies are available.

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Graphical abstract We developed an immunochromatographic electrochemical biosensor (IEB) for highly specific and sensitive determination of Hg(II) ions in water and milk by using a new anti-Hg²⁺ monoclonal antibody (McAb). The linear range and limit of detection is 0.1–200 ng·mL^?1 and 30 pg.mL^?1, respectively.

     

Cockle shell-derived nanoparticles for optical urea biosensor development based on reflectance transduction

An optical biosensor for urea based on urease enzyme immobilised on functionalised calcium carbonate nanoparticles (CaCO₃-NPs) was successfully developed in this study. CaCO₃-NPs were synthesised from discarded cockle shells via a simple and eco-friendly approach, followed by surface functionalisation with succinimide ester groups. The fabricated biosensor is comprised of two layers. The first (bottom layer) contained functionalised NPs covalently immobilised to urease, and the second (uppermost layer) was alginate hydrogel physically immobilised to the pH indicator phenolphthalein. The biosensor provided a colorimetric indication of increasing urea concentrations by changing from colourless to pink. Quantitative urea analysis was performed by measuring the reflectance intensity of the colour change at a wavelength of 633.16 nm. The determination of urea concentration using this biosensor yielded a linear response range of 30–1000 mM (R² = 0.9901) with a detection limit of 17.74 mM at pH 7.5. The relative standard deviation of reproducibility was 1.14%, with no signs of interference by major cations, such as K⁺, Na⁺, NH?⁺, and Mg²⁺. The fabricated biosensor showed no significant difference with the standard method for the determination of urea in urine samples.     

The chromatographic behavior of group (IIB) metal ions on polyurethane foam functionalized with 8-hydroxyquinoline

Polyurethane foam functionalized with 8-hydroxyquinoline has been prepared by coupling the foam matrix with 8-hydroxyquinoline (oxine) through an azo spacer. The oxine-bonded foam (Ox PUF) was characterized by use of different tools (UV–Vis spectra, IR spectra, density, and stability). Ox PUF was found to be very suitable for separation and preconcentration of trace metals, e.g. Zn(II), Cd(II), and Hg(II) ions, from wastewater in the pH ranges 2–12, 9–12, and 3–6, respectively. Various conditions influencing the sorption of these metal ions on to Ox PUF were optimized. Extraction of the metal ions was accomplished in 15 to 20 min. Study of the variation of the sorption of the tested metal ions with temperature yielded average values for H, S, and G of 41.99, 158.23, and –5.1 kJ mol^–1, respectively. The capacities of the foam material were 0.27, 0.16, and 0.09 mmol g^–1 for Zn(II), Cd(II), and Hg(II), respectively. Preconcentration factors >50 were achieved (RSD6.18). The quantitative results were obtained from experiments performed using certified reference materials.     

Lead ion-selective electrodes based on polyphenylenediamine as unique solid ionophores

A novel membrane electrode for Pb(II) ion detection based on semi-conducting poly(m-phenylenediamine) microparticles as a unique solid ionophore was fabricated. The electrode exhibited significantly enhanced response towards Pb(II) over the concentration range from 3.16 × 10⁻⁶ to 0.0316 M at pH 3.0-5.0 with a low detection limit of 6.31 × 10⁻⁷ M, a high sensitivity displaying a near-Nernstian slope of 29.8 mV decade⁻¹ for Pb(II). The electrode showed a long lifetime of 5 months and a short response time of 14 s. A systematical investigation on the effect of anion excluder and various foreign ions on the selectivity of the electrode by a fixed interference method suggests that all other metal ions hardly ever interfere with the determination of Pb(II) except high concentration Hg(II). The electrode was successfully used as an indicator electrode in the potentiometric titration of Pb(II) with EDTA. Furthermore, the electrode has been used to satisfactorily analyze four types of real-world samples like spiked human urine, spiked tap water, and river water containing interfering ions like Na(I), Ca(II), Mg(II), Zn(II), Pd(II), Fe(III), K(I), Cu(II) and Hg(II) up to 8.04 × 10⁻⁴ M, demonstrating fast response, high selectivity, good recovery (96.6-121.4%), good repeatability (RSD 0.31-6.45%), and small relative error (5.0%).     

Simultaneous trace-levels determination of Hg(II) and Pb(II) ions in various samples using a modified carbon paste electrode based on multi-walled carbon nanotubes and a new synthesized Schiff base

A modified carbon paste electrode based on multi-walled carbon nanotubes (MWCNTs) and 3-(4-methoxybenzylideneamino)-2-thioxothiazolodin-4-one as a new synthesized Schiff base was constructed for the simultaneous determination of trace amounts of Hg(II) and Pb(II) by square wave anodic stripping voltammetry. The modified electrode showed an excellent selectivity and stability for Hg(II) and Pb(II) determinations and for accelerated electron transfer between the electrode and the analytes. The electrochemical properties and applications of the modified electrode were studied. Operational parameters such as pH, deposition potential and deposition time were optimized for the purpose of determination of traces of metal ions at pH 3.0. Under optimal conditions the limits of detection, based on three times the background noise, were 9.0 × 10⁻⁴ and 6.0 × 10⁻⁴ μmol L⁻¹ for Hg(II) and Pb(II) with a 90 s preconcentration, respectively. In addition, the modified electrode displayed a good reproducibility and selectivity, making it suitable for the simultaneous determination of Hg(II) and Pb(II) in real samples such as sea water, waste water, tobacco, marine and human teeth samples.     

A mercury(II) ion-selective electrode based on neutral salicylaldehyde thiosemicarbazone

A new ion-selective PVC membrane electrode based on salicylaldehyde thiosemicarbazone as an ionophore is developed successfully as sensor for mercury(II) ions. The electrode shows excellent potentiometric response characteristics and displays a linear log[Hg²⁺] versus EMF response over a wide concentration range of 1.778×10⁻⁶-1.0×10⁻¹ M with Nernstian slope of 29 mV per decade with the detection limit of 1.0×10⁻⁶ M. The response time of the electrode is less than 30 s and the membrane electrode operates well in the pH range of 1.0-3.0. The lifetime of the sensor is about 2 months. The electrode shows better selectivity towards Hg²⁺ ions in comparison with the alkali, alkaline and some heavy metal ions; most of these metal ions do not show significant interference (K^Pot_Hg,M values of the order of 10⁻³-10⁻⁴). The present sensor showed comparable or even better performance vis-à-vis similar PVC based ion-selective electrodes reported in literature. The sensor was also applied as an indicator electrode for potentiometric titration of Hg²⁺ions with I⁻ and Cr₂O₇²⁻.     

Cation exchange column chromatography in aqueous ammonium acetate: Separation of U(VI), Al(III), Sr(II), Ba(II) and Hg(II) from other metal ions

Summary A rigorous analysis of the effect of various concentrations (0.02–1.60M) of ammonium acetate on the distribution coefficients (K) of a number of metal ions using cation exchanger Dowex 50W-X8 (100–200 mesh NH₄ ⁺-form) has been made. On account of the low affinity of U(VI) for resin in 0.20M NH₄OAc it can be separated from all other metal ions. HighK values of Sr(II), Ba(II) and Hg(II) at higher 0.50M NH₄OAc are responsible for their separation from others. The abnormal column Chromatographic behaviour of Al(III) permits its separation from other metal ions including U(VI), Sr(II), Ba(II), Hg(II). A number of binary and ternary separations have been achieved.     

New solid phase extractors for selective separation and preconcentration of mercury (II) based on silica gel immobilized aliphatic amines 2-thiophenecarboxaldehyde Schiff’s bases

2-Thiophenecarboxaldhyde is chemically bonded to silica gel surface immobilized monoamine, ethylenediamine and diethylenetriamine by a simple Schiff’s base reaction to produce three new SP-extractors, phases (I-III). The selectivity properties of these phases toward Hg(II) uptake as well as eight other metal ions: Ca(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) were extensively studied and evaluated as a function of pH of metal ion solution and equilibrium shaking time by the batch equilibrium technique. The data obtained clearly indicate that the new SP-extractors have the highest affinity for retention of Hg(II) ion. Their Hg(II) uptake in mmol g⁻¹ and distribution coefficient as log K_d values are always higher than the uptake of any other metal ion along the range of pH used (pH 1.0-10.0). The uptake of Hg(II) using phase I was 2.0 mmol g⁻¹ (log K_d 6.6) at pH 1.0 and 2.0. 1.8 mmol g⁻¹ (log K_d 4.25), 1.6 mmol g⁻¹ (log K_d 3.90) and 1.08 mmol g⁻¹ (log K_d 3.37) at pH 3.0, 5.0 and 8.0, respectively. Selective separation of Hg(II) from the other eight coexisting metal ions under investigation was achieved successfully using phase I at pH 2.0 either under static or dynamic conditions. Hg(II) was completely retained while Ca(II), Co(II) and Cd(II) ions were not retained. Ni(II), Cu(II), Zn(II), Pb(II) and Fe(III) showed very low percentage retention values to be 0.74, 0.97, 3.5 and 6.3%, respectively. Moreover, the high recovery values (95.5 ± 0.5, 95.8 ± 0.5 and 99.0% ± 1.0) of percolating two liters of doubly distilled water, drinking tap water and Nile river water spiked with 5 ng/l of Hg(II) over 100 mg of phase I packed in a minicolumn and used as a thin layer enrichment bed demonstrate the accuracy and validity of the new SP-extractors for preconcentration of the ultratrace amount of spiked Hg(II) prior to the determination by borohydride generation atomic absorption spectrometry (AAS) with no matrix interference. The detection limit (3σ) for Hg(II) based on enrichment factor 1000 was 4.75 pg/ml. The precision (R.S.D.) obtained for different amounts of mercury was in the range 0.52-1.01% (N = 3) at the 25-100 ng/l level.     

A porphyrin derivative containing 2-(oxymethyl)pyridine units showing unexpected ratiometric fluorescent recognition of Zn2+ with high selectivity

A porphyrin derivative (1), containing two 2-(oxymethyl)pyridine units has been designed and synthesized as chemosensor for recognition of metal ions. Unlike many common porphyrin derivatives that show response to different heavy metal ions, compound 1 exhibits unexpected ratiometric fluorescence response to Zn²⁺ with high selectivity. The response of the novel chemosensor to zinc was based on the porphyrin metallation with cooperating effect of 2-(oxymethyl)pyridine units. The change of fluorescence of 1 was attributed to the formation of an inclusion complex between porphyrin ring and Zn²⁺ by 1:1 complex ratio (K = 1.04 × 10⁵), which has been utilized as the basis of the fabrication of the Zn²⁺-sensitive fluorescent chemosensor. The analytical performance characteristics of the proposed Zn²⁺-sensitive chemosensor were investigated. The sensor can be applied to the quantification of Zn²⁺ with a linear range covering from 3.2 × 10⁻⁷ to 1.8 × 10⁻⁴ M and a detection limit of 5.5 × 10⁻⁸ M. The experiment results show that the response behavior of 1 to Zn²⁺ is pH-independent in medium condition (pH 4.0-8.0) and show excellent selectivity for Zn²⁺ over transition metal cations.     

Differential Pulse Stripping Voltammetry of Mercury(II) Ions at a Cylindrical Carbon-Fiber Microelectrode in the Presence of Au(III) Ions

The determination of Hg(II) ions in aqueous solutions containing Au(III) ions was studied using differential pulse stripping voltammetry at a cylindrical carbon-fiber (d= 30 m) microelectrode fabricated from a pitch at 2800°C. At the [Au(III)]/[Hg(II)] ratio higher than 25, the anodic voltammogram of mercury accumulated in the potential range from 0.2 to –0.2 V for 40–200 s exhibited a current peak at 0.62–0.72 V. The peak height and area were directly proportional to the concentration of Hg(II) in the range (1–1000) × 10^–10M. The results of determining Hg(II) in waters of different origin are reported.     

2,3-Dihydroxypyridine-loaded cellulose: a new macromolecular chelator for metal enrichment prior to their determination by atomic absorption spectrometry

New macromolecular chelators have been synthesized, by loading 2,3-dihydroxypyridine (DHP) on cellulose via linkers -NH-CH₂-CH₂-NH-SO₂-C₆H₄-N=N- and -SO₂-C₆H₄-N=N-, and characterized by elemental analysis, TGA, IR, and CPMAS ¹³C NMR spectra. The cellulose with DHP anchored by the shorter linker had better sorption capacity (between 69.7 and 431.1 mol g^–1) for Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II), and Fe(III)) than the other (51.9–378.1 mol g^–1); the former was therefore studied in detail as a solid extractant for these metal ions. The optimum pH ranges for quantitative sorption (recovery 97.6–99.8%) on this matrix were: 7.0–9.0, 6.0–9.0, 3.0–8.0, 6.0–8.0, 6.0–9.0, 6.0–7.0, and 2.0–6.0 respectively. Desorption was quantitative with 0.5 mol L^–1 HCl and 0.5 mol L^–1 HNO₃ (for Pb). Simultaneous sorption (at pH 7.0) of all metal ions other than Fe(III) was possible if their total concentration did not exceed the sorption capacity (lowest value). The recovery of seven metal ions from their mixture at pH 6.0 was nearly quantitative when the concentration level of each metal ion was 0.2 g mL^–1. The optimum flow rate of metal ion solutions for quantitative sorption of metal onto a column packed with DHP-modified cellulose was 2–7 mL min^–1, whereas for desorption the optimum flow rate for the acid solution was 2–4 mL min^–1. The time needed to reach 50% of the total loading capacity (t_1/2) was <5 min for all the metal ions except Ni and Pb. The limit of detection (blank+3s) was from 0.70 to 4.75 g L^–1 and the limit of quantification (blank+10s) was between 0.79 and 4.86 g L^–1. The tolerance limits for NaCl, NaBr, NaI, NaNO₃, Na₂SO₄, Na₃PO_4, humic acid, EDTA, Ca(II), and Mg(II) for sorption of all metal ions are reported. The column packed with DHP-anchored cellulose can be reused at least 20 times for enrichment of metal ions in water sample. It has been used to enrich all the metal ions in pharmaceutical and water samples before their determination by flame AAS. RSD for these determinations was between 1.1 and 6.9%.     

Selective solid-phase extraction of trace mercury(II) using a silica gel modified with diethylenetriamine and thiourea

We describe a solid phase extractor for selective separation and preconcentration of Hg(II) ion. It was prepared by immobilizing the adduct of diethylenetriamine and thiourea on silica gel. The effects of solution acidity, preconcentration time, sample flow rate and volume were optimized. The results show that Hg(II) can be selectively extracted from acidic solutions and in presence of common other metal ions. The adsorbent is stable, can be reused more than 10 times, and the maximum adsorption capacity is 23 mg g^?1. Hg(II) was quantified by inductively coupled plasma optical emission spectrometry. The method has a detection limit of 23 ng L^?1, and the relative standard deviation is <2 %. The procedure was validated by analyzing two standard materials (river sediment and hair powder), and was successfully applied to the preconcentration of Hg(II) in real samples.