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.     

Sorptive potential of sunflower stem for Cr(III) ions from aqueous solutions and its kinetic and thermodynamic profile

The sorptive potential of sunflower stem (180-300 μm) for Cr(III) ions has been investigated in detail. The maximum sorption (≥85%) of Cr(III) ions (70.2 μM) has been accomplished using 30 mg of high density sunflower stem in 10 min from 0.001 M nitric and 0.0001 M hydrochloric acid solutions. The accumulation of Cr(III) ions on the sorbent follows Dubinin-Radushkevich (D-R), Freundlich and Langmuir isotherms. The isotherm yields D-R saturation capacity X_m = 1.60 ± 0.23 mmol g⁻¹, β = −0.00654 ± 0.00017 kJ² mol⁻², mean free energy E = 8.74 ± 0.12 kJ mol⁻¹, Freundlich sorption capacity K_F = 0.24 ± 0.11 mol g⁻¹, 1/n = 0.90 ± 0.04 and of Langmuir constant K_L = 6800 ± 600 dm³ mol⁻¹ and C_m = 120 ± 18 μmol g⁻¹. The variation of sorption with temperature (283-323 K) gives ΔH = −23.3 ± 0.8 kJ mol⁻¹, ΔS = −64.0 ± 2.7 J mol⁻¹ K⁻¹ and ΔG_298k = −4.04 ± 0.09 kJ mol⁻¹. The negative enthalpy and free energy envisage exothermic and spontaneous nature of sorption, respectively. Bisulphate, Fe(III), molybdate, citrate, Fe(II), Y(III) suppress the sorption significantly. The selectivity studies indicate that Cr(III), Eu(III) and Tb(III) ions can be separated from Tc(VII) and I(I). Sunflower stem can be used for the preconcentration and removal of Cr(III) ions from aqueous medium. This cheaper and novel sorbent has potential applications in analytical and environmental chemistry, in water decontamination, industrial waste treatment and in pollution abatement. A possible mechanism of biosorption of Cr(III) ions onto the sunflower stem has been proposed.     

Sulfonylcalix[4]arenetetrasulfonate as pre-column chelating reagent for selective determination of aluminum(III), iron(III), and titanium(IV) by ion-pair reversed-phase high-performance liquid chromatography with spectrophotometric detection

Sulfonylcalix[4]arenetetrasulfonate (SO₂CAS) has been examined as a pre-column chelating reagent for ultratrace determination of metal ions by ion-pair reversed-phase high-performance liquid chromatography with spectrophotometric detection. Metal ions were converted into the SO₂CAS chelates in an acetic buffer solution (pH 4.7). The chelates were injected onto a n-octadecylsilanized silica-type Chromolith™ Performance RP-18e column and were eluted using a methanol (50 wt.%)-water eluent (pH 5.6) containing tetra-n-butylammonium bromide (7.0 mmol kg⁻¹), acetate buffer (5.0 mmol kg⁻¹), and disodium ethylendiamine-N,N,N′,N′-tetraacetate (0.10 mmol kg⁻¹). Under the conditions used, Al(III), Fe(III), and Ti(IV) were selectively detected among 21 kinds of metal ions [Al(III), Ba(II), Be(II), Ca(II), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Ga(III), Hf(IV), In(III), Mg(II), Mn(II), Mo(VI), Ni(II), Pb(II), Ti(IV), V(V), Zn(II), and Zr(IV)]. The detection limits on a 3σ blank basis were 8.8 nmol dm⁻³ (0.24 ng cm⁻³) for Al(III), 7.6 nmol dm⁻³ (0.42 ng cm⁻³) for Fe(III), and 17 nmol dm⁻³ (0.80 ng cm⁻³) for Ti(IV). The practical applicability of the proposed method was checked using river and tap water samples.     

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.     

Sequestration of Cu(II), Ni(II), and Co(II) by ethyleneimine immobilized on silica

Thermodynamic data on interaction of Cu(II), Ni(II), and Co(II) with silica modified with ethyleneimine are obtained by calorimetric titration. The amount of ethyleneimine anchored on silica surface was estimated to be 0.70 mmol g⁻¹. The enthalpies of binding Ni(II), Cu(II) and Co(II), are −3.59 ± 0.001, −4.88 ± 0.001, and −7.75 ± 0.003 kJ mol⁻¹, respectively.     

Determination of mercury species with a resin functionalized with a 1,2-bis(o-aminophenylthio)ethane moiety

A method for the simultaneous preconcentration and determination of Hg(II) and MeHg(I) at the ng ml⁻¹ level has been developed. This method is based on solid phase extraction using a newly synthesized chelating resin containing nitrogen and sulphur donor sites of the 1,2-bis(o-aminophenylthio)ethane moiety that is very selective for mercury. The characterization of the resin has been carried out by elemental analyses, infrared spectral data, thermogravimetric analysis and metal ion capacities. The resin is highly selective for Hg(II) and MeHg(I) with an exchange capacity of 0.38 and 0.30 mmol g⁻¹, respectively. Various parameters like pH, column flow rate, desorbing agents are optimized. Cold vapour atomic absorption spectrometry (CVAAS) was used to measure the concentration of both species of mercury. The calibration graph was linear upto 10 ng ml⁻¹ with a 3σ detection limit of 0.09 ng ml⁻¹. The recovery of Hg(II) and MeHg(I) was found to be 98.9±2.0 and 98.0±1.1%, respectively. The method has been used for routine determination of trace levels of mercury species in natural waters to comply with more stringent regulations.     

Solid phase extraction of trace Hg(II) on silica gel modified with 2-(2-oxoethyl)hydrazine carbothioamide and determination by ICP-AES

In this work, a new 2-(2-oxoethyl)hydrazine carbothioamide modified silica gel (SG-OHC) sorbent was prepared and applied for preconcentration of trace mercury(II) prior to the measurement by inductively coupled plasma atomic emission spectrometry (ICP-AES). The optimization of some analytical parameters affecting the adsorption of the analyte such as acidity, shaking time, sample flow rate and volume, eluent condition, and interfering substances were investigated. At pH 3, the maximum static adsorption capacity of Hg(II) onto the SG-OHC was 37.5 mg g⁻¹. The quantitative recovery (>95%) of Hg(II) could be obtained using 2 mL of 0.5 mol L⁻¹ HCl and 1% CS(NH₂)₂ solution as eluent. Common coexisting substances did not interfere with the separation of mercury(II) under optimal conditions. The detection limit of present method was 0.10 ng mL⁻¹, and the relative standard deviation (RSD) was lower than 4.0% (n = 8). The prepared sorbent was successfully applied for the preconcentration of trace Hg(II) in certified and water samples with satisfactory results.     

Cold vapour atomic fluorescence determination of mercury in milk by slurry sampling using multicommutation

A highly sensitive mechanized method has been developed for the determination of mercury in milk by atomic fluorescence spectrometry (AFS). Samples were sonicated for 10 min in an ultrasound water bath in the presence of 8% (v/v) aqua regia, 2% (v/v) antifoam A and 1% (m/v) hydroxilamine hydrochloride, and after that, they were treated with 8 mmol l⁻¹ KBr and 1.6 mmol l⁻¹ KBrO₃ in an hydrochloric medium. Atomic fluorescence measurements were made by multicommutation, which provides a fast alternative in quality control analysis, due to the easy treatment of a large number of samples (approximately 70 h⁻¹), and is an environmentally friendly procedure, which involves a waste generation of only 94.5 ml h⁻¹ as compared with the 605 ml h⁻¹ obtained by using continuous AFS measurements. The limit of detection found was 0.011 ng g⁻¹ Hg in the original sample. The method provided a relative standard deviation of 3.4% for five independent analysis of a sample containing 0.30 ng g⁻¹ Hg. To validate the accuracy of the method, a certified reference material NIST-1459 (non-fat milk powder) containing 0.3±0.2 ng g⁻¹ Hg was analysed and a value of 0.27±0.06 ng g⁻¹ Hg was found. A comparison made between data found by the developed procedure and those obtained by microwave-assisted digestion and continuous AFS measurements evidenced a good comparability between these two strategies. Results obtained for commercially available milk samples varied between 0.09 and 0.61 ng g⁻¹ Hg depending on the type of sample and its origin. The confluence of the analytical waste with a 6 mol l⁻¹ NaOH allowed us to reduce the waste generation in a working session from 1 l to 5 g solid residue with a matrix of Fe(OH)₃ which contributes to the deactivation of traces of heavy metals presents in the samples that does not form volatile hydrides.     

Highly selective preconcentration of Cu(II) from seawater and water samples using amidoamidoxime silica

Chemically modified silica containing amidoamidoxime group was studied as a sorbent for solid-phase extraction (SPE) and preconcentration of Cu(II) prior to determination by flame atomic absorption spectrometry (FAAS). The sorbent showed an extremely high selectivity towards Cu(II) in the pH range of 4-6, while the extraction of Pb(II), Cd(II), Ni(II) and Co(II) was low. The adsorption isotherm followed the Langmuir model and the maximum sorption capacity of 0.0163 mmol Cu(II) g⁻¹ was achieved. In the flow system, Cu(II) was completely retained on a column containing 40 mg of the modified silica at the flow rate of 4.0 mL min⁻¹ and quantitatively eluted by 5 mL of 1% (v/v) HNO₃. No interference from Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻ and SO₄²⁻ at 10, 100 and 1000 mg L⁻¹ was observed. When applied for preconcentration and determination of Cu(II) in tap water, pond water, and seawater, the recoveries were 96, 101, and 95%, respectively, with high precision (% relative standard deviation (R.S.D.) < 4) and low method detection limit (9 μg L⁻¹).     

Synthesis,characterization of low density polyhydroxy polyurethane foam and its application for separation and determination of gold in water and ores samples

In this work, a new type of sorbent (low density polyhydroxy polyurethane Foam, LPPF) was synthesis by using water hydrolysis of polyurethanediazonium chloride salt. LPPF was characterized using different tools e.g. elemental analysis, UV–vis and IR spectra, TGA, SEM, density and pH_ZPC. It was tested for separation, preconcentration and determination of gold in environmental samples using batch and dynamic techniques. The sorption experimental data was fitted by the pseudo-first kinetic mathematical equation (R² = 0.991). The sorption rate of the Au (III) ions is very fast, the half-life (t_1/2) ≈ 34 s. The equilibrium process is well described by the Freundlich isotherm model, the R² value is 0.967, which attributed to the heterogeneous surface structure of the LPPF. The breakthrough capacity of LPPF and the recovery of gold ions were 0.36 mmol g⁻¹ (70.5 mg g⁻¹) and 99–100%, respectively. The lower detection limit of gold by using spectrophotometric method is 3.3 ng L⁻¹ with preconcentration factors ≈ 450 (RSD ∼ 1.66%, n = 4). The values of ΔG and ΔH for the sorption of gold onto LPPF were −12.5 and −103.5 kJ mol⁻¹, respectively, which indicate that the sorption of Au (III) onto LPPF is spontaneous and exothermic reaction. The obtained results indicate that the ion chelation and ion association might be the most probable mechanism of gold sorption onto LPPF. The study shows LPPF has the potential of application as an efficient sorbent for the extraction and determination of gold in water, gold alloys pharmaceutical and granite samples.     

Host hydrated barium phenylphosphonate/guest heterocyclic amine intercalation energetics by calorimetric titration

The heterocyclic amines 2,6-lutidine, pyrazine, piperazine and piperidine were intercalated into layered crystalline hydrated barium phenylphosphonate, Ba(HO₃PC₆H₅)₂·H₂O, through a batch method in ethanolic solution, to give the maximum amounts 0.39, 0.82, 2.80 and 5.50 mmol g⁻¹, respectively. The original host interlayer distance (d) of 1532 pm increased after intercalation for piperazine (1752 pm) and piperidine (2112 pm) molecules, while for 2,6-lutidine and pyrazine molecules d values were maintained. The enthalpy of intercalation gave −5.60 ± 0.10, −1.00 ± 0.02, −9.55 ± 1.00 and −30.70 ± 0.68 kJ mol⁻¹ for the sequence of heterocyclic amines. The Gibbs free energies are negative and entropies are positive for intercalation.     

Aluminum phosphate dispersed on a cellulose acetate fiber surface: Preparation, characterization and application for Li, Na and K separation

Cellulose acetate fibers with supported highly dispersed aluminum phosphate were prepared by reacting aluminum-containing cellulose acetate (Al₂O₃=3.5 wt.%; 1.1 mmol g⁻¹ aluminum atom per gram of the material) with phosphoric acid. Solid-state NMR spectra (CPMAS ³¹P NMR) data indicated that HPO₄²⁻ is the species present on the fiber surface. The specific concentration of acidic centers, determined by ammonia gas adsorption, is 0.50 mmol g⁻¹. The ion exchange capacities for Li⁺, Na⁺ and K⁺ ions were determined from ion exchange isotherms at 298 K and showed the following values (in mmol g⁻¹): Li⁺=0.03, Na⁺=0.44 and K⁺=0.50. The H⁺/Li⁺ exchange corresponds to the model of the ideal ion exchange with a small value of the corresponding equilibrium constant K=1.1×10⁻². Due to the strong cooperative effect, the H⁺/Na⁺ and H⁺/K⁺ ion exchange is non-ideal. These ion exchange equilibria were treated with the use of models of fixed bi- or tridentate centers, which consider the surface of the sorbent as an assemblage of polyfunctional sorption centers. Both the observed ion exchange capacities with respect to the alkaline metal ions and the equilibrium constants were discussed by taking into consideration the sequence of the ionic hydration radii for Li⁺, Na⁺ and K⁺. The matrix affinity order for the ions decreases as the hydration radii of the cations increase, i.e. Li⁺>Na⁺>K⁺. The high values of the separation factors S_Na⁺/Li⁺ and S_K⁺/Li⁺ (up to several hundred) provide quantitative separation of Na⁺ and K⁺ from Li⁺ from a mixture containing these three ions.     

Trace determination of thiosulphate and thioglycolic acid using novel inhibitory kinetic spectrophotometric method

Sulphur containing compounds such as sodium thiosulphate (STS) and thioglycolic acid (TGA) inhibit the rate of cyanide substitution by nitroso-R-salt (NRS) in hexacyanoruthenate(II) catalysed by Hg(II) ions due to their strong binding tendencies with Hg(II) catalyst. This inhibitory effect of sodium thiosulphate and thioglycolic acid is used as the basis for their determination at micro levels. The reaction was followed spectrophotometrically at 525 nm (λ_max of [Ru(CN)₅NRS]³⁻ complex) under optimised reaction conditions at 8.75 × 10^− 5 M [Ru(CN)₆⁴⁻], 3.50 × 10^− 4 M [NRS], pH 7.00 ± 0.02, ionic strength (µ) 0.1 M (KCl) and temp 45.0 ±0.1 °C. The modified mechanistic scheme is proposed to understand the inhibition caused by sulphur containing compounds (STS and TGA) on Hg(II) catalysed substitution of cyanide by NRS in [Ru(CN)₆]⁴⁻. The range of analytical concentration of inhibitor depends upon two factors; the amount of Hg(II) catalyst present in the indicator reaction and the stability of the Hg(II)-inhibitor complex under consideration. Under optimum conditions STS and TGA have been determined in the range of 0.98-7.0 × 10^− 6 M and 0.30-7.0 × 10^− 6 M. The detection limits for STS and TGA were found to be 3.0 × 10^− 7 M and 1.0 × 10^− 7 M respectively.     

Use of 1-(2-pyridylazo)-2-naphthol as the post column reagent for ion exchange chromatography of heavy metals in environmental samples

Ion exchange chromatography (IEC) using a bi-functional column (quaternary ammonium and sulfonate groups), followed by post-column reaction (PCR) with 1-(2-pyridylazo)-2-naphthol (PAN), was used to separate and quantitate Cu(II), Ni(II), Zn(II), Co(II), Cd(II), Mn(II) and Hg(II) at low concentration levels. IEC-PCR separation was achieved within 14 min using the mobile phase containing 3 mmol L^− 1 2,6-pyridinedicarboxylic acid (PDCA) and 3 mmol L^− 1 oxalate at pH 12.5. Effects of pH as well as PAN, detergent and chloride ion concentrations during post-column reaction on detector response were examined. Detection limits were less than 4.5 μg L^− 1 for all metals except Hg(II) (19 μg L^− 1) using spectrophotometric measurements at 550 nm. Analytical validations showed good linearity for detection up to 6.0 mg L^− 1, with R² higher than 0.99. Precisions based on retention time evaluation for intra-day and inter-day measurements with the relative standard deviation (RSD) were less than 2.9% and 3.6%, respectively. The method gave good accuracy with the recoveries ranged from 80.5 to 105% for all metal ions studied. The proposed method was applied to the analysis of metal ions in environmental samples (leachate, soil and sediment) in Northeastern Thailand. The results were in good agreement with atomic spectroscopic measurements on the same samples.     

Combined cation-exchange and extraction chromatographic method of pre-concentration and concomitant separation of Cu(II) with high molecular mass liquid cation exchanger after its online detection

A selective method has been developed for the extraction chromatographic trace level separation of Cu(II) with Versatic 10 (liquid cation exchanger) coated on silanised silica gel (SSG-V10). Cu(II) has been extracted from 0.1 M acetate buffer at the range of pH 4.0–5.5. The effects of foreign ions, pH, flow-rate, stripping agents on extraction and elution have been investigated. Exchange capacity of the prepared exchanger at different temperatures with respect to Cu(II) has been determined. The extraction equilibrium constant (K_ex) and different standard thermodynamic parameters have also been calculated by temperature variation method. Positive value of ΔH (7.98 kJ mol⁻¹) and ΔS (0.1916 kJ mol⁻¹) and negative value of ΔG (−49.16 kJ mol⁻¹) indicated that the process was endothermic, entropy gaining and spontaneous. Preconcentration factor was optimized at 74.7 ± 0.2 and the desorption constants K_desorption¹(1.4 × 10⁻²) and K_desorption²(9.8 × 10⁻²) were determined. The effect of pH on R_f values in ion exchange paper chromatography has been investigated. In order to investigate the sorption isotherm, two equilibrium models, the Freundlich and Langmuir isotherms, were analyzed. Cu(II) has been separated from synthetic binary and multi-component mixtures containing various metal ions associated with it in ores and alloy samples. The method effectively permits sequential separation of Cu(II) from synthetic quaternary mixture containing its congeners Bi(III), Sn(II), Hg(II) and Cu(II), Cd(II), Pb(II) of same analytical group. The method was found effective for the selective detection, removal and recovery of Cu(II) from industrial waste and standard alloy samples following its preconcentration on the column. A plausible mechanism for the extraction of Cu(II) has been suggested.     

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.     

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.     

New microdialysis-electrochemical device for simultaneous determination of ascorbic acid and 5-hydroxyindole-3-acetic acid in rat striatum

A new device combining microdialysis with electrochemical microsensor was developed. It can be applied to monitor the biomolecules in the brain for biological and pharmaceutical research. In this paper, the device was applied to simultaneously determine ascorbic acid (AA) and 5-hydroxyindole-3-acetic acid (5-HIAA) in rat striatum. The microsensor used for the device was poly (sulphosalicylic acid) microsensor, which exhibited a good electrocatalytic effect on oxidization of AA and 5-HIAA. The oxidation currents measured by differential pulse voltammetry (DPV) were linear for AA in the range of 0.02-1.0 mmol l⁻¹, and for 5-HIAA from 0.5 to 10.0 μmol l⁻¹ (r=0.9998 and 0.9991, respectively). The detection limits were calculated to be 0.01 mmol l⁻¹ for AA and 0.25 μmol l⁻¹for 5-HIAA (S/N=3). Studies also showed that co-existing substances in biological fluids did not interfere with AA and 5-HIAA determination when using this microsensor. Since, the substances in the microdialysate are easily oxidized by air, the microdialysate in this device was under the protection of N₂. It was found that the concentrations of AA and 5-HIAA in rat striatum were 215±5 and 6.21±0.61 μmol l⁻¹ (mean±S.E.M., n=7), respectively with this device under the protection of N₂. In addition, the effect of the nitric oxide donor, sodium nitroprusside (SNP), on 5-HIAA in the rat striatum was investigated. It was found that a high concentration of SNP (1.0 mmol l⁻¹) resulted in a 34% increase in 5-HIAA level.     

Kinetic determination of cysteine and thiosulphate by inhibition of Hg(II) catalyzed ligand substitution reaction

The sulphur containing inhibitors (I), cysteine (Cys) and sodium thiosulphate (THS), have been found to inhibit Hg(II) catalyzed exchange of cyanide in hexacyanoferrate(II) by nitroso-R-salt (NRS). The inhibitory effect of both the ligands are attributed to their binding tendencies with Hg(II) leading to the formation of catalyst-inhibitor (C-I) complex. The reactions have been followed spectrophotometrically in aqueous medium at 720 nm by noting the increase in absorbance of the green colour product, [Fe(CN)₅NRS]³⁻ at pH 6.50 ± 0.02, temp 25.0 ± 0.1 °C and ionic strength (μ) 0.1 M (KNO₃). A most plausible mechanistic scheme involving the role of analytes (inhibitors) has been proposed. The values of equilibrium constants for complex formation between catalyst-inhibitor (K_CI), catalyst-substrate (K_S) and Mechaelis-Menton constant (K_m) have been computed from the kinetic data. The linear calibration curves have been established between absorbance and inhibitor concentrations under specified conditions. Cys and THS have been determined in the range 1-5 × 10^− 7 M and 4.9-16.9 × 10^− 7 M respectively. The detection limits have been computed to be 1 × 10^− 7 M and 4.9 × 10^− 7 M for Cys and THS, respectively.     

Separation and determination of trace amounts of zinc, lead, cadmium and mercury in tap and Qaroun lake water using polyurethane foam functionalized with 4-hydroxytoluene and 4-hydroxyacetophenone

A stable chelating sorbent was synthesized by covalently linking 4-hydroxytoluene or 4-hydroxyacetophenone with the polyurethane foam (PUF) through -NN- group. The synthesized chelating sorbents were characterized by IR and UV/vis measurements. The modified foams show excellent stability towards various solvents. Factors influencing the extraction process of Zn(II), Pb(II), Cd(II) and Hg(II) were studied and evaluated as a function of pH of metal ion solution and equilibration shaking time. The values of sorption capacity of metal ions (μg g⁻¹) were determined with the two types of bonded foams. The two phenolic bonded foams were studied comparatively. The potential applications of the two newly synthesized foams for the removal and separation of the examined metal ions from two natural water samples (drinking tap water and Qaroun lake water at Fayoum City, Egypt) were investigated. Precision (assessed as a relative standard deviation, R.S.D.) was also evaluated and found to be ≤7.3% (N = 5) with a detection limit under 0.46 μg L⁻¹.