Derivatization of 2-chlorophenol with 4-amino-anti-pyrine: a novel method for improving the selectivity of molecularly imprinted solid phase extraction of 2-chlorophenol from water

Molecularly imprinted polymer (MIP) may not selectively recognize small template of limited number of functional groups, such as 2-chlorophenol (2-CP). In this work, a novel method was proposed to improve the recognition ability of the molecularly imprinted solid phase extraction (MISPE) of 2-CP from environmental waters. This was achieved by derivatization of 2-CP with 4-amino-anti-pyrine (4-AAP) to enlarge its molecular size and add more binding sites. For that purpose, two MISPE methods of 2-CP were developed. In method 1, a polymer imprinted with 2-CP was used as the extracting sorbent but it suffered from low selectivity and high detection limit of 2-CP (7.10 ng L⁻¹). In method 2, a polymer imprinted with 4-AAP derivatized 2-CP (2-CP-4-AAP) was used as the extracting sorbent. Prior to loading the water sample it was subjected to a simple derivatization procedure with 4-AAP. Method 2 showed high recognition ability/selectivity towards 2-CP-4-AAP with lower detection limit of 0.05 ng L⁻¹ for 2-CP-4-AAP. Method 2 was able to detect the presence of 2-CP-4-AAP in unspiked real water samples and almost full spike recovery was achieved.     

Evaluation of a magnetic polysulfone microcapsule containing organic modified montmorillonite as a novel solid-phase extraction sorbent with chlorophenols as model compounds

A porous polysulfone microcapsule containing organic modified montmorillonite and magnetic nanoparticles (OMMT-Fe₃O₄@PSF) has been successfully prepared by a phase-inversion method and evaluated as a magnetic solid-phase extraction (MSPE) sorbent for clean-up and enrichment of 4-chlorophenol (4-CP) and 2-chlorophenol (2-CP) in aqueous samples. Compared with a microcapsule containing the conventional extraction sorbent C18 (C18-Fe₃O₄@PSF), OMMT-Fe₃O₄@PSF had much lower cost, a faster adsorption rate, and superior uptake amounts for the investigated analytes. The proposed microcapsule has been developed for the extraction of 4-CP and 2-CP from environmental water samples and their analysis by high-performance liquid chromatography with UV detection (HPLC-UV). Various parameters, such as pH, extraction time, the mass of sorbent, and the desorption conditions, have been evaluated and the calibration curves of the chlorophenols were linear (R² ≥ 0.9985) in the range from 1.01 to 104.5 ng mL⁻¹. The limits of detection at a signal-to-noise (S/N) ratio of 3 were 0.22 and 0.17 ng mL⁻¹ and the limits of quantification calculated at S/N = 10 were 1.52 and 1.07 ng mL⁻¹ for 2-CP and 4-CP, respectively. The recoveries of 2-CP and 4-CP from natural water and the treated wastewater samples were in the range of 84.4-115% with relative standard deviations (RSDs) lower than 7.0%. The results have demonstrated the suitability of the MSPE approach for the analysis of trace chlorophenols in aqueous samples.     

The petentiometric determination of peroxide hydrogen and glucose on the glassy electrode modified by the calix[4]arene

A new petentiometric method to determine peroxide hydrogen and glucose had been studied. This method had been applied on the petentiometric determination of peroxide hydrogen and glucose in the total ionic strength adjustment buffer (TISAB) (pH 7.5) solution with the glassy electrode modified by the calix[4]arene. The glassy carbon electrode covered with the calix[4]arene depended on the H₂O₂ concentration in the range of log[H₂O₂] from −3.3 to −1.2 in the solution of TISAB (pH 7.5) with nearly Nernstian slope of about 65.6 ± 3 mV and the detection limit of peroxide hydrogen was 4.0 × 10⁻⁵ mol L⁻¹. The glassy carbon electrode covered with the calix[4]arene depended on the glucose concentration in the range of log[glucose] from −3.6 to −2.8 in the solution of TISAB (pH 7.5) with nearly Nernstian slope of about 50.2 ± 2 mV and the detection limit of glucose was 2.0 × 10⁻⁵ mol L⁻¹. The electrode had the good selectivity, sensitivity, stability and repeatability.     

Determination of selenium using atomically imprinted polymer (AIP) and hydride generation atomic absorption spectrometry

This paper describes selenium determination based on Se⁰ preconcentration in the imprinted polymer (synthesized with 2.25 mmol SeO₂, 4-vinylpyridine and 1-vinylimidazole) with subsequent detection on-line in HG-FAAS. During the synthesis, SeO₂ is reduced to Se (0). Therefore, there are no MIP neither IIP in the present work, thus we denominated: AIP, i.e., atomically imprinted polymers. For the optimization of analytical parameters Doehlert design was used. The method presented limit of detection and limit of quantification of 53 and 177 ng L⁻¹, respectively, and linear range from 0.17 up to 6 μg L⁻¹ (r = 0.9936). The preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were 232; 0.06 mL and 58 min⁻¹ respectively. The proposed method was successfully applied to determine Se in Brazil nuts (0.33 ± 0.03 mg kg⁻¹), apricot (0.46 ± 0.02 mg kg⁻¹), white bean (0.47 ± 0.03 mg kg⁻¹), rice flour (0.47 ± 0.02 mg kg⁻¹) and milk powder (0.22 ± 0.01 mg kg⁻¹) samples. It was possible to do 12 analyzes per hour. Accuracy was checked and confirmed by analyzing certified reference material (DORM-2, dogfish muscle), and samples precision was satisfactory with RSD lower than 10%.     

Performance of the diffusive gradients in thin films technique for measurement of trace metals in low ionic strength freshwaters

A series of experiments were undertaken to investigate the effect of ionic strength and the concentration of free sodium ions in the resin gel on the performance of the diffusive gradients in thin films (DGT) technique. When the free sodium ion concentration in the resin gel was estimated by the time-dependent release into solution, it agreed with a previous estimate. However, equilibration with different volumes of water gave a higher value, suggesting that inherent averaging in the time-dependent release method underestimates the free concentration. DGT measurements of Cu and Cd were made over a wide range of ionic strengths (from 3 μmol l⁻¹ to 0.8 mol l⁻¹). For all the ionic strengths above 100 μmol l⁻¹ there was no significant difference between measurements made by DGT and measurements made directly on the solution using atomic absorption spectroscopy. Below 100 μmol l⁻¹ results were erratic. They did not comply with a theory that predicts high results for DGT based on enhancement of the diffusion coefficient of trace metal cations by counter diffusion of sodium ions. When Cd in solutions with a range of ionic strengths was measured by DGT there was no difference whether the resin gels were in Na or Ca form. Rather than counter diffusion of Na ions, it is suggested that the spurious behaviour at low ionic strength is due to interactions of the trace metals with the diffusion gel when there are insufficient excess cations present.     

Synthesis by precipitation polymerisation of molecularly imprinted polymer microspheres for the selective extraction of carbamazepine and oxcarbazepine from human urine

Two molecularly imprinted polymers (MIPs), in the physical form of well-defined polymer microspheres, were synthesised via precipitation polymerisation (PP) using an antiepileptic drug, carbamazepine (CBZ), as template molecule, methacrylic acid as functional monomer and either divinylbenzene 80 (DVB-80) or a mixture of DVB-80 and ethylene glycol dimethacrylate (EGDMA) as crosslinking agents. The MIP obtained using DVB-80 alone as crosslinking agent (MIP A) had a narrow particle size distribution (9.5 ± 0.5 μm) and a well-developed permanent pore structure (specific surface area in the dry state = 758 m² g⁻¹), whereas when a mixture of DVB-80 and EGDMA (MIP B) were used as crosslinking agents, the polymer obtained had a broader particle size distribution (6.4 ± 1.8 μm) and a relatively low specific surface area (23 m² g⁻¹). The molecular recognition character of both polymers was evaluated by means of LC and then a molecularly imprinted solid-phase extraction (MISPE) protocol; CBZ was recognised by both polymers, and useful cross-selectivity for oxcarbazepine (OCBZ), which is the main metabolite of CBZ, also observed. In a detailed bioanalytical study, MIP A was selected in preference to MIP B since MIP A enabled a high volume of sample to be extracted such that lower limits of detection were achievable using this polymer. High recoveries of CBZ and OCBZ were obtained in a MISPE protocol when 50 mL of human urine spiked at 0.2 mg L⁻¹ were percolated through MIP A (90% and 83%, respectively).     

Sensitive and selective electrochemical determination of quinoxaline-2-carboxylic acid based on bilayer of novel poly(pyrrole) functional composite using one-step electro-polymerization and molecularly imprinted poly(o-phenylenediamine)

A facile and efficient molecularly imprinted polymer (MIP) recognition element of electrochemical sensor was fabricated by directly electro-polymerizing monomer o-phenylenediamine (oPD) in the presence of template quinoxaline-2-carboxylic acid (QCA), based on one-step controllable electrochemical modification of poly(pyrrole)-graphene oxide-binuclear phthalocyanine cobalt (II) sulphonate (PPY-GO-BiCoPc) functional composite on glassy carbon electrode (GCE). The MIP film coated on PPY-GO-BiCoPc functional composite decorated GCE (MIP/PPY-GO-BiCoPc/GCE) was presented for the first time. The synergistic effect and electro-catalytic activity toward QCA redox of PPY-GO-BiCoPc functional composite were discussed using various contrast tests. Also, the effect of experimental variables on the current response such as, electro-polymerization cycles, template/monomer ratio, elution condition for template removal, pH of the supporting electrolyte and accumulation time, were investigated in detail. Under the optimized conditions, the proposed MIP sensor possessed a fast rebinding dynamics and an excellent recognition capacity to QCA, while the anodic current response of square wave voltammetry (SWV) was well-proportional to the concentration of QCA in the range of 1.0 × 10⁻⁸–1.0 × 10⁻⁴ and 1.0 × 10⁻⁴–5.0 × 10⁻⁴ mol L⁻¹ with a low detection limit of 2.1 nmol L⁻¹. The established sensor was applied successfully to determine QCA in commercial pork and chicken muscle samples with acceptable recoveries (91.6–98.2%) and satisfactory precision (1.9–3.5% of SD), demonstrating a promising feature for applying the MIP sensor to the measurement of QCA in real samples.     

Nanostructured progesterone immunosensor using a tyrosinase-colloidal gold-graphite-Teflon biosensor as amperometric transducer

A novel progesterone immunosensor using a colloidal gold-graphite-Teflon-tyrosinase composite biosensor as amperometric transducer is reported. A sequential competitive configuration between the analyte and progesterone labelled with alkaline phosphatase (AP) was used. Phenyl phosphate was employed as the AP-substrate and the enzyme reaction product, phenol, was oxidized by tyrosinase to o-quinone, which is subsequently reduced at −0.1 V at the biocomposite electrode. Variables such as the concentration of phenyl phosphate, the amount of antibody attached to the electrode surface, immersion time in a 2% BSA solution, working pH and incubation times in progesterone and AP conjugate were optimized. A linear calibration graph for progesterone was obtained between 0 and 40 ng mL⁻¹ with a slope value of −82.3 nA ng⁻¹ mL, and a detection limit of 0.43 ng mL⁻¹. The time needed to reach the steady-state current from the addition of phenyl phosphate was 30-40 s. These analytical characteristics improve substantially those reported for other progesterone immunosensors. A lifetime of 14 days with no need to apply any regeneration procedure was also achieved. The usefulness of the immunosensor was evaluated by determining progesterone in milk samples spiked with the analyte at 5.0 and 1.5 ng mL⁻¹ concentration levels. Following a very simple procedure, involving only sample dilution, mean recoveries (n = 7) of 98 ± 3% and 99 ± 3%, respectively, were obtained.     

Laser induced fluorescence and photochemical derivatization for trace determination of camptothecin

Laser-excited fluorescence was used for the selective determination of camptothecin in samples containing anti-cancer camptothecin-analogs (irinotecan and topotecan). The selectivity of the method was based on the UV photochemical derivatization in basic solution which increased the analyte fluorescence (337/450 nm) and eliminated fluorescence from the two campthotecin-analogs. The influence of UV exposure time and sodium hydroxide concentration was studied using an experimental design. Limit of detection was 4 × 10⁻¹⁰ mol L⁻¹ with linear fluorescence response up to 1 × 10⁻⁶ mol L⁻¹. Average recoveries of camptothecin (added to the samples to simulate a contamination) were 92 ± 4 and 94 ± 6% (n = 3) respectively in irinotecan and topotecan based pharmaceuticals.     

Comparative study of 2-hydroxy propyl beta cyclodextrin and calixarene as ionophores in potentiometric ion-selective electrodes for neostigmine bromide

Three novel neostigmine bromide (NEO) selective electrodes were investigated with 2-nitrophenyl octyl ether as a plasticiser in a polymeric matrix of polyvinyl chloride (PVC). Sensor 1 was fabricated using tetrakis(4-chlorophenyl)borate (TpClPB) as an anionic exchanger without incorporation of an ionophore. Sensor 2 used 2-hydroxy propyl β-cyclodextrin as an ionophore while sensor 3 was constructed using 4-sulfocalix-8-arene as an ionophore. Linear responses of NEO within the concentration ranges of 10⁻⁵ to 10⁻², 10⁻⁶ to 10⁻² and 10⁻⁷ to 10⁻² mol L⁻¹ were obtained using sensors 1, 2 and 3, respectively. Nernstian slopes of 51.6 ± 0.8, 52.9 ± 0.6 and 58.6 ± 0.4 mV/decade over the pH range of 4-9 were observed. The selectivity coefficients of the developed sensors indicated excellent selectivity for NEO. The utility of 2-hydroxy propyl β-cyclodextrin and 4-sulfocalix[8]arene as ionophores had a significant influence on increasing the membrane sensitivity and selectivity of sensors 2 and 3 compared to sensor 1. The proposed sensors displayed useful analytical characteristics for the determination of NEO in bulk powder, different pharmaceutical formulations, and biological fluids (plasma and cerebrospinal fluid (CSF)) and in the presence of its degradation product (3-hydroxyphenyltrimethyl ammonium bromide) and thus could be used for stability-indicating methods.     

A microflow chemiluminescence system for determination of chloramphenicol in honey with preconcentration using a molecularly imprinted polymer

A novel chemiluminescence (CL) microfluidic system incorporating a molecularly imprinted polymer (MIP) preconcentration step was used for the determination of chloramphenicol in honey samples. The MIP was prepared by using chloramphenicol as the template, diethylaminoethyl methacrylate (DAM) as the function monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linking monomer, 2, 2′-dimethoxy-2-phenylacetophenone (DMPA) as the free radical initiator and toluene and dodecanol as the solvent. The MIP was pre-loaded into a 10 mm long, 2 mm wide and 150 μm deep channel in a planar glass microfluidic device. When the sample containing chloramphenicol was introduced into the microfluidic device it was first preconcentrated on the MIP then detected by an enhancement effect on the chemiluminescence reaction of tris(2, 2′-bipyridyl) ruthenium(II) with cerium(IV) sulphate in sulphuric acid. A micro-syringe pump was used to pump the reagents. The CL intensity was linear in relationship to the chloramphenicol concentrations from 1.55 × 10⁻⁴ to 3.09 × 10⁻³ μmol L⁻¹ (r² = 0.9915) and the detection limit (3σ) and the quantitation limit (10σ) were found to be 7.46 × 10⁻⁶ and 2.48 × 10⁻⁵ μmol L⁻¹, respectively. This method offered a high selectivity and sensitivity for quantitative analysis of chloramphenicol in the honey samples.     

Synthesis and thermochemistry of SrB2O4·4H2O and SrB2O4

Two pure strontium borates SrB₂O₄·4H₂O and SrB₂O₄ have been synthesized and characterized by means of chemical analysis and XRD, FT-IR, DTA-TG techniques. The molar enthalpies of solution of SrB₂O₄·4H₂O and SrB₂O₄ in 1 mol dm⁻³ HCl(aq) were measured to be −(9.92 ± 0.20) kJ mol⁻¹ and −(81.27 ± 0.30) kJ mol⁻¹, respectively. The molar enthalpy of solution of Sr(OH)₂·8H₂O in (HCl + H₃BO₃)(aq) were determined to be −(51.69 ± 0.15) kJ mol⁻¹. With the use of the enthalpy of solution of H₃BO₃ in 1 mol dm⁻³ HCl(aq), and the standard molar enthalpies of formation for Sr(OH)₂·8H₂O(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpies of formation of −(3253.1 ± 1.7) kJ mol⁻¹ for SrB₂O₄·4H₂O, and of −(2038.4 ± 1.7) kJ mol⁻¹ for SrB₂O₄ were obtained.     

Factorial design for Fe, Cu, Zn, Se and Pb preconcentration optimization with APDC and analysis with a portable X-ray fluorescence system

Preconcentration of heavy metals in water with ammonium pyrrolydine dithiocarbamate (APDC) is a common practice in analytical chemistry. A literature review on this topic showed that several authors use this precipitation agent, but in different preconcentration conditions, conducting to divergent results. The objective of this work is to use factorial design to optimize the factors involved in the preconcentration process of heavy metals using APDC. Five factors were studied: sample volume, solution pH, APDC concentration, APDC volume and stirring time. The assays were performed by energy dispersive X-ray fluorescence (EDXRF). The values for detection limits within 95% confidence level, in μg L⁻¹, were: Fe (6.0 ± 0.1), Cu (4.0 ± 0.1), Zn (2.0 ± 0.1), Se (4.0 ± 0.1) and Pb (5.0 ± 0.1). The value for quantification limit for the five elements was 20 μg L⁻¹, with 3% deviation. Multi-element standard solutions were prepared. Precipitation procedure was applied in the spiked solutions and the samples were filtered in cellulose ester membrane for quantification measurements. The optimum values obtained were 300 mL of sample solution, pH 4, 1 mL of 2% APDC and 10 min of stirring time. The concentration results obtained for the validation measurements were satisfactory for in situ survey employing a portable instrument.     

A new kinetic method for quantification phenoxyl free radicals

In this work, a new kinetic method was proposed for quantification phenoxyl radicals generated in enzyme reaction. Instead of direct detecting the spectral signals of phenoxyl radicals, a molecular probe, the reduced form of nicotinamide adenine dinucleotide (NADH), was employed to indicate the formation of phenoxyl free radicals. It was found that the reactions of NADH and phenoxyl radicals are very fast, but can be followed by using stopped-flow fast scanning spectrophotometric technique. The initial rate of accelerated-oxidation of NADH represents the reactivity of phenoxyl free radical, which is proportional in a certain range to the initial concentration of the parent chlorophenols of the radicals. With this method, the phenoxyl radicals generated in oxidation reaction of chlorophenols (2-CP; 4-CP; 2,4-DCP; 2,4,6-TCP and 2,3,4,6-Tetra-CP) with hydrogen peroxide, catalyzed by horseradish peroxidase, were investigated. The method is highly sensitive. Phenoxyl radicals generated from as low as 1 × 10⁻⁸ M 2,4-DCP, for example, can be readily detected with the proposed method. The results show that the reactivity of various phenoxyl radicals are in the following order: 2,4-DCP > 4-CP > 2-CP > 2,4,6-TCP > 2,3,4,6-Tetra-CP. A mechanism is proposed to explain the possible pathway of the probe reaction. The feasibility of this method was assessed by the determination of enzymatic generation of phenoxyl radicals in lake water samples.     

A highly selective molecularly imprinted electrochemiluminescence sensor for ultra-trace beryllium detection

A new molecularly imprinted electrochemiluminescence (ECL) sensor was proposed for highly sensitive and selective determination of ultratrace Be²⁺ determination. The complex of Be²⁺ with 4-(2-pyridylazo)-resorcinol (PAR) was chosen as the template molecule for the molecularly imprinted polymer (MIP). In this assay, the complex molecule could be eluted from the MIP, and the cavities formed could then selectively recognize the complex molecules. The cavities formed could also work as the tunnel for the transfer of probe molecules to produce sound responsive signal. The determination was based on the intensity of the signal, which was proportional to the concentrations of the complex molecule in the sample solution, and the Be²⁺ concentration could then be determined indirectly. The results showed that in the range of 7 × 10⁻¹¹ mol L⁻¹ to 8.0 × 10⁻⁹ mol L⁻¹, the ECL intensity had a linear relationship with the Be²⁺ concentrations, with the limit of detection of 2.35 × 10⁻¹¹ mol L⁻¹. This method was successfully used to detect Be²⁺ in real water samples.     

Basic study on the determination of total boron by conversion to tetrafluoroborate ion (BF4) followed by ion chromatography

The basic study on the determination of tetrafluoroborate ion (BF₄⁻) by ion chromatography, and total boron by conversion of boric acid to BF₄⁻ followed by ion chromatography of BF₄⁻ has been carried out. The results of thermodynamic calculations for the system of boric acid (H₃BO₃)-F⁻-H⁺ showed that the mole fraction of BF₄⁻ was higher than 99% at pH lower than 3.5 and 4.5 when the total free fluoride concentration (2[H₂F₂] + 2[HF₂⁻] + [HF] + [F⁻]) was as high as 0.1 and 1.0 M, respectively. The fraction of BF₄⁻ increased with increasing total free fluoride concentration. BF₄⁻ fraction values were higher than 99% at pH 0.75 and at total free fluoride concentration of 0.05 M or higher. BF₄⁻ was hardly formed at pH > 7 even when the total free fluoride concentration was as high as 1.0 M. According to the experimental results, the fraction of BF₄⁻ at pH 0.7-0.8 was 51.2, 95.6 and 96.7% when the total fluoride concentration (2[H₂F₂] + 2[HF₂⁻] + [HF] + [F⁻] + 3[BF₃OH⁻] + 4[BF₄⁻]) was 0.2, 1.0 and 3.3 M, respectively. The formation reaction of BF₄⁻ from boric acid reached an equilibrium state within 20 min regardless of reaction temperature, in the range of 20-50 °C, when the total boron and total fluoride concentrations were 66.7 mM and 1.0 M, respectively. Although BF₄⁻ was formed only under acidic conditions, BF₄⁻, once formed, was very stable under alkaline conditions at least for several hours. We have concluded that BF₄⁻ could be analyzed by ion chromatography using sodium hydroxide solution as an eluent because BF₄⁻ was stable under chromatographic conditions. BF₄⁻ solution prepared from boric acid could be used as a standard solution in the ion chromatographic analysis of BF₄⁻ instead of the sodium tetrafluoroborate (NaBF₄) reagent available commercially, if a discrepancy of about 4-5% was allowed.     

Novel preconcentration technique using bis(2-ethylhexyl) hydrogen phosphate (HDEHP) loaded porous polytetrafluoroethylene (PTFE) filter tube as a sorbent: Its application to determination of In(III) in seawater by ICP-MS with air segmented discrete sample introduction

Novel preconcetration method involving porous polytetrafluoroethylene (PTFE) filter tube impregnated bis(2-ethylhexyl) hydrogen phosphate (HDEHP) as a sorbent was studied to establish it as a practical preconcentration method for ultra trace analysis with ICP-MS. A 1 ng portion of In(III) in 1000 ml of matrix free solution or 700 ml of synthetic seawater was quantitatively complexated with HDEHP adsorbed onto porous PTFE filter tube by passing the solution through the micro pore of the filter tube. Preconcentrated In(III) was then quantitatively recovered provided that the elution, which consists of a cyclical filtering 0.1 ml of 8 mol dm⁻³ hydrochloric acid through the filter tube for 1 min; therefore, up to 10000- and 7000-fold of enrichment was attained for matrix free solution and synthetic seawater, respectively. To introduce a 0.1 ml of the eluted solution to ICP-MS, flow injection method with air segmented discrete sample introduction (ASDI) was also studied by using manually operated simple valve system. By using ASDI, good linearity of calibration curve (r = 0.99997) was observed from 0.01 to 5.0 ng ml⁻¹ of In(III). Good reproducibility was also shown in measurements of 0.1 ml of 5 ng ml⁻¹ of In(III) (R.S.D. = 1.9%, n = 5). The average recovery and R.S.D. of the results for the five duplicates determination of 0.1 ng of In(III) spiked to 200 ml of synthetic seawater were 99 and 2.4%, respectively. The method was applied to the determination of In(III) in coastal seawater sampled at north east of Hachijyo Island, Japan; using 200 ml of sample, 2000-fold preconcentration of In(III) was performed within 30 min for five samples. The analytical detection limit and the blank were 9.8 and 21 pg l⁻¹, respectively. The average concentration was determined to be 96 pg l⁻¹, and R.S.D. of the results was 3.7% (n = 3).     

Direct colorimetric detection of copper(II) ions in sampling using diffusive gradients in thin-films

A novel binding phase was developed for use in diffusive gradients in thin-film (DGT) sampling for Cu(II) by employing methylthymol blue as a chelating and chromogenic agent. Methylthymol blue was adsorbed onto beads of Dowex 1 × 8 resin (200-400 mesh) and the resin beads were then immobilised onto an adhesive disc. Analysis of exposed binding discs by either UV-vis spectrophotometry or computer imaging densitometry provided robust quantification of adsorbed Cu(II) in the 0.2-1 μg cm⁻² range, allowing detection at μg L⁻¹ concentrations in the test solution (ca. 17 μg L⁻¹ for a 24 h deployment), and in good agreement with established DGT theory. The method was shown to be a potential replacement for binding phases based on Chelex 100 where a colorimetric response to a specific metal is desired.     

Heat capacity and thermodynamic functions of LuPO4 in the range 0-320 K

The heat capacity of LuPO₄ was measured in the temperature range 6.51-318.03 K. Smoothed experimental values of the heat capacity were used to calculate the entropy, enthalpy and Gibbs free energy from 0 to 320 K. Under standard conditions these thermodynamic values are: (298.15 K) = 100.0 ± 0.1 J K⁻¹ mol⁻¹, S⁰(298.15 K) = 99.74 ± 0.32 J K⁻¹ mol⁻¹, H⁰(298.15 K) − H⁰(0) = 16.43 ± 0.02 kJ mol⁻¹, −[G⁰(298.15 K) − H⁰(0)]/T = 44.62 ± 0.33 J K⁻¹ mol⁻¹. The standard Gibbs free energy of formation of LuPO₄ from elements Δ_fG⁰(298.15 K) = −1835.4 ± 4.2 kJ mol⁻¹ was calculated based on obtained and literature data.     

Retention, kinetics and thermodynamics profile of cadmium adsorption from iodide medium onto polyurethane foam and its separation from zinc bulk

The sorption behaviour of 2.5 × 10⁻⁵ M solution of Cd(II) on polyurethane foam (PUF) from iodide medium have been investigated. The conditions were optimized from aqueous solutions of different pH (1-10) and of acids of varied concentration (0.01-1.0 M). The maximum concentration of KI was found to be 0.24 M and equilibration time was established to be 20 min. The data successfully followed the Freundlich and Dubinin-Radushkevich (D-R) isotherms at low metal ion concentration while Langmuir isotherm followed at higher metal ion concentration. The Freundlich parameter 1/n = 0.66 ± 0.02 have been evaluated whereas D-R isotherm yields the sorption free energy E = 10.5 ± 0.1 kJ mol⁻¹ indicating ion exchange type chemisorption. The monolayer coverage (XL) constant of Langmuir isotherm was found to be 23.7 ± 0.4 mg g⁻¹. The numerical values of thermodynamics parameters enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG) indicated the endothermic and spontaneous nature of sorption. The Scatchard plot analysis was tested to evaluate the binding sites of the PUF and stability constants of sorption were determined. On the basis of these parameters, the sorption mechanism was discussed. Among the foreign ions tested, Pb(II), Hg(II), cyanide and nitrite should be absent. The clean separation of Cd(II) from Zn(II) ions in the ratio 1:250, respectively, was achieved by column chromatography.