DAPPA grafted polymer: an efficient solid phase extractant for U(VI), Th(IV) and La(III) from acidic waste streams and environmental samples

A new class of polymeric resin has been synthesized by grafting Merrifield chloromethylated resin with (dimethyl amino-phosphono-methyl)-phosphonic acid (MCM-DAPPA), for the preconcentration of U(VI), Th(IV) and La(III) from both acidic wastes and environmental samples. The various chemical modification steps involved during grafting process are characterized by FT-IR spectroscopy, ³¹P and ¹³C-CPMAS (cross-polarized magic angle spin) NMR spectroscopy and CHNS/O elemental analysis. The water regain capacity data for the grafted polymer are obtained from thermo-gravimetric (TG) analysis. The influence of various physico-chemical parameters during the quantitative extraction of metal ions by the resin phase are studied and optimized by both static and dynamic methods. The significant feature of this grafted polymer is its ability to extract both actinides and lanthanides from high-level acidities as well as from near neutral conditions. The resin shows very high sorption capacity values of 2.02, 0.89 and 0.54 mmol g⁻¹ for U(VI), 1.98, 0.63 and 0.42 mmol g⁻¹ for Th(IV) and 1.22, 0.39 and 0.39 mmol g⁻¹ for La(III) under optimum pH, HNO₃ and HCl concentration, respectively. The grafted polymer shows faster phase exchange kinetics (<5 min is sufficient for 50% extraction) and greater preconcentration ability, with reusability exceeding 20 cycles. During desorption process, all the analyte ions are quantitatively eluted from the resin phase with >99.5% recovery using 1 M (NH₄)₂CO₃, as eluent. The developed grafted resin has been successfully applied in extracting Th(IV) from high matrix monazite sand, U(VI) from sea water and also U(VI) and Th(IV) from simulated nuclear spent fuel mixtures. The analytical data obtained from triplicate measurements are within 3.9% R.S.D. reflecting the reproducibility and reliability of the developed method.     

Selective extraction of U(VI) over Th(IV) from acidic streams using di-bis(2-ethylhexyl) malonamide anchored chloromethylated polymeric matrix

A new chelating polymeric sorbent has been developed using Merrifield chloromethylated resin anchored with di-bis (2-ethylhexyl) malonamide (DB2EHM). The modified resin was characterized by CPMAS NMR spectroscopy, FT-NIR-FIR spectroscopy, CHN elemental analysis and also by thermo gravimetric analysis. The fabricated sorbent showed superior binding affinity for U(VI) over Th(IV) and other diverse ions, even under high acidities. Various physio-chemical parameters, like solution acidity, phase exchange kinetics, metal sorption capacity, electrolyte tolerance studies, etc., influencing the resin’s metal extractive behavior were studied by both static and dynamic method. Batch extraction studies performed over a wide range of solution acidity (0.01-10 M) revealed that selective extraction of U(VI) could be achieved even up to 4 M acidity with distribution ratios (D) in the order of ∼10³. The phase exchange kinetics studies performed for U(VI) and Th(IV) revealed that time duration of <15 min was sufficient for >99.5% extraction. But similar studies when preformed for trivalent lanthanides gave very low D values (<50), with the extraction time extending up to 60 min. The metal sorption studies performed for U(VI) and Th(IV) at 5 M HNO₃ was found to be 62.5 and 38.2 mg g⁻¹,respectively. Extraction efficiency in the presence of inferring electrolyte species and inorganic cations were also examined. Metal ion desorption was effective using 10-15 mL of 1 M (NH₄)₂CO₃ or 0.5 M α-hydroxy isobutyric acid (HIBA). Extraction studies performed on a chromatographic column at 5 M acidity were found to give enrichment factor values of 310 and 250 for U(VI) and Th(IV), respectively. The practical utility of the fabricated chelating sorbent and its efficiency to extract actinides from acidic waste streams was tested using a synthetic nuclear spent fuel solution. The R.S.D. values obtained on triplicate measurements (n = 3) were within 5.2%.     

Selective enrichment of U(VI), Th(IV) and La(III) from high acidic streams using a new chelating ion-exchange polymeric matrix

An off-line extraction chromatographic technique has been developed using Amberlite XAD-16 (AXAD-16)-N,N-dihexylcarbamoylmethyl phosphonic acid, as the stationary phase for the extraction of uranium, thorium and lanthanum from nuclear spent fuels as well as from geological and natural water resources. The chemical modifications of the polymeric matrix were monitored using FT-IR spectroscopy, CHNPS elemental analysis and also by thermo gravimetric analysis for water regain measurements. Various physio-chemical parameters influencing the quantitative metal ion extraction by the resin phase were optimized by both static and dynamic methods. The developed resin matrix showed good distribution ratio values under wide concentrations of acidity and pH conditions. Moreover, the sequential separation of analytes is also possible at sample pH 6.5. Also, the polymeric matrix showed superior metal sorption capacities and rapid metal exchange kinetics with a high sample flow rate value of 26 cm³ min⁻¹ for all the three analytes. Thus, reducing the time of analyte extraction from large number of samples anticipated in nuclear waste management programs. The quantitative metal ion recovery of >99.8% was effected with 0.5 M (NH₄)₂CO₃ solution. The method was highly sensitive with lower limits of detections to be 10, 20 and 15 ng cm⁻³ for U(VI), Th(IV) and La(III), respectively, with a better pre-concentration values of 333 for U(VI) and Th(IV) and 400 for La(III), respectively paving way for its applicability in pre-concentrating trace analytes from large sample volumes. The analytical data were within 4.2% R.S.D. reflecting the reproducibility and reliability of the developed method.     

Adamantylcalixarenes with CMPO groups at the wide rim: synthesis and extraction of lanthanides and actinides

Starting from p-adamantylcalix[4]- and [6]arenes functionalized with carboxylic acid or ester groups at the adamantane nuclei, carbamoylmethylphosphine oxide (CMPO)-containing ligands of a novel type were synthesized. They were studied as extractants for a series of f-block elements including radioactive ¹⁵²Eu(III), ²⁴¹Am(III), ²³³U(VI), and ²³⁹Pu(IV). Tetrameric ligand 4b in which CMPO residues are connected to adamantane nuclei through methylene groups gave the best extraction results for lanthanides and actinides. For all the ligands the extraction efficiency does not decrease at higher nitric acid concentration. Although the discrimination between trivalent actinides and lanthanides is not good, all ligands are highly selective for thorium(IV) with the best separation factor achieved in the case of hexameric ligand 5 (D_Th/D_Ln>24).     

On the mechanism of trivalent actinide extraction in the system HDEHP—Lactic acid with DTPA

The dependence of the distribution coefficients on the hydrogen ion concentration and HDEHP concentration in the process of extraction from lactic acid solutions in the presence of DTPA and without it has been investigated. It has been shown that when the lactate ion concentration is higher than 0.01M, Cm is extracted predominantly as the first lactate complex. The presence of DTPA does not change the extraction mechanism. Similarity of the observed regularities for trivalent actinides and lanthanides is confirmed by the extraction of Bk(III), Ce(III), and Eu(III). It is suggested that the nature of carbonic acid used in TALSPEAK-process greatly influences the efficiency of group separation of TPE and lanthanides. It is supported by some experimental data. The extraction and stability constants of the first lactate complex (Cm Lact²⁺) have been found to be: K_e=2, β ₁ ⁰ = 7,7 · 10³. In the practical lactic acid concentration range (1 M) the unextractable complex, Cm Lact₃, is also formed in the aqueous phase. The stability constant of this complex has been found to be β ₃ ⁰ = 1.2 · 10⁷.     

Liquid-liquid extraction and recovery of indium using Cyanex 923

The extraction of In(III) from HCl, H₂SO₄, and HNO₃ media using a 0.20 mol l⁻¹ Cyanex 923 solution in toluene is investigated. In(III) is quantitatively extracted over a fairly wide range of HCl molarity while from H₂SO₄ and HNO₃ media the extraction is quantitative at low acid concentration. The extracted metal ion has been recovered by stripping with 1.0 mol l⁻¹ H₂SO₄. The stoichiometry of the In(III): Cyanex 923 complex is observed to be 1:2. The extraction of In(III) is insignificantly changed in diluents namely toluene, n-hexane, kerosene (160-200 °C), cyclohexane, and xylene having more or less the same dielectric constants, whereas, it decreases with increasing polarity of diluents such as cyclohexanone and chloroform. The extractant is stable towards prolonged acid contact and there is a negligible loss in its extraction efficiency even after recycling for 20 times. The extraction behavior of some commonly associated metal ions namely V(IV), Ti(IV), Al(III), Cr(III), Fe(III), Ga(III), Sb(III), Tl(III), Mn(II), Fe(II), Cu(II), Zn(II), Cd(II), Pb(II), and Tl(I) has also been investigated. Based on the partition data the conditions have been identified for attaining some binary separations of In(III). These conditions are extended for the recovery of pure indium from zinc blend, zinc plating mud, and galena. The recovery of the metal ions is around 95% with purity approximately 99%.     

Thermal and luminescence characterization of lanthanide 2,6-naphthalenedicarboxylates series

The lanthanide 2,6-naphthalenedicarboxylates series of the formulas Ln₂(ndc)₃·nH₂O, where Ln = lanthanides from La(III) to Lu(III); ndc - C₁₀H₆(COO)₂²⁻; n = 4, 4.5 or 5 have been prepared by the precipitation method. All obtained products were examined and characterized by elemental analysis, FTIR spectroscopy, simultaneous thermal analyses TG-DSC and TG-FTIR, X-Ray diffraction patterns as well as luminescence measurements. The crystalline compounds form three isostructural groups: Ce-Sm; La and Eu-Dy; Ho-Lu. In all complexes, the ndc²⁻ ligand appears in the deprotonated form. Heating of the complexes resulted in the multi-steps decomposition process. The dehydration process leads to the formation of stable crystalline Ln₂ndc₃ compounds which further decompose to the corresponding lanthanide oxides (air atmosphere). In argon atmosphere they decompose with releasing of water, carbon oxides and naphthalene molecules. The luminescence properties of Eu(III), Nd(III), Tb(III) and Er(III) complexes were investigated. The complexes of Eu(III) and Tb(III) emitted red and green light when excited by ultraviolet light whereas Nd(III) and Er(III) display emissions in the NIR region.     

Anionic alkyl diglycoldiamides with covalently bonded cobalt bis(dicarbollide)(1−) ions for lanthanide and actinide extractions

Ionic diamides composed of a N,N′-dialkyl diglycolyl complexing group and two cobalt bis(dicarbollide)(1−) anions were synthesized with the aim to develop efficient extraction agents for liquid-liquid extraction of polyvalent cations, i.e. lanthanides and actinides from high-level activity nuclear waste. Compounds of general formulation [{(N,N-(8-CH₂-CH₂O)₂-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Co)(N′,N′-R)NCOCH₂}₂O]Na₂, where R = n-C₄H₉, n-C₈H₁₇, n-C₁₂H₂₅ and 1-C₆H₄-4-CH₃ (1-4), were prepared and characterized by combination of ¹¹B ¹H, ¹³C NMR spectroscopy, ESI-MS, HPLC and other techniques. Effects of different nitrogen substitution in the structures of 1-4 on the extraction properties were tested. The study resulted in the observation that the compounds are significantly (2-3 orders in magnitude) more efficient extractants for Eu(III) and Am(III) than synergic mixtures of organic N,N′-tetra n-octyl diglycolic acid diamide (TODGA) and chlorinated cobalt bis(dicarbollide) at the same concentrations of both groups. Low polar mixtures of n-dodecane (D) and hexyl methyl ketone (HMK) can be applied as an auxiliary solvent for extraction, replacing thus the polar and less environmentally friendly nitro-, fluoro- and chloro- solvents used in the current dicarbollide liquid-liquid extraction process.     

Synthesis of fluorinated malonamides and use in L/L extraction of f-elements

Synthesis of new fluorinated tertiary malonamides (F-malonamides) was accomplished, and their liquid/liquid (L/L) extraction properties with f-elements were investigated. These molecules are fluorinated analogues of well known extractants used in several processes designed towards the treatment of nuclear wastes, and the efficient separation of lanthanides from minor actinides; however, the synthesis of F-malonamides deserved a modification of the general synthetic route commonly employed to prepare H-malonamides. Extraction of neodymium from various aqueous media into both fluorous and classical solvents was studied, which revealed an opposite trend between F-malonamides and H-malonamides: L/L extraction ability is very sensitive to the nitrogen atoms substitution pattern, and the most efficient F-malonamide is compound 3 (R₁ = Me), whereas the best H-malonamide is compound 5 (R₁ = Bu, DMDBTDMA).     

Synthesis,DNA binding and antitumor activities of some novel polymer–cobalt(III) complexes containing 1,10-phenanthroline ligand

The novel water-soluble polymer–cobalt(III) complex samples, cis-[Co(phen)₂(BPEI)Cl]Cl₂ · 4H₂O (phen = 1,10-phenanthroline, BPEI = branched polyethyleneimine), with different amounts of cobalt complex content in the polymer chain, were prepared by ligand substitution method in water–ethanol medium and characterized by Infra-red, UV–Vis, ¹H NMR spectral and elemental analysis methods. The interaction of these polymer–cobalt(III)-phenanthroline complex samples with calf thymus DNA has been explored using electronic absorption spectroscopy, emission spectroscopy and gel electrophoresis techniques. The presence of multiple small size molecular binding sites, namely, the cobalt(III)–phenanthroline complex moieties, and free amino groups in a single big sized polymer molecule enhanced both the electrostatic and/or van der Waals interaction and partial intercalative bindings with calf thymus DNA. The antitumor activity of a sample of polymer–cobalt(III) complex was determined using HEp-2 cell line and different cell death indicator stains and MTT assay. Many of the cultured HEp-2 cells treated with this complex suffered loss of viability and death mostly through apoptosis as evidenced by the nuclear and cytoplasmic morphology.     

Colorimetric detection of uranium(VI) on building surfaces after enrichment by solid phase extraction

A method for detecting and quantifying uranium(VI) levels on building materials that include concrete, Plexiglas, glass and steel surfaces is presented. Uranium(VI) was extracted from building material surfaces using a pH 2.2 buffer rinse and, subsequently complexed by an organic chelating agent, arsenazo III. The application of a uranium-chelating molecule, arsenazo III, allows for concentration enhancement using C₁₈ solid phase extraction and colorimetric detection of the uranium complex using ultraviolet-visible spectroscopy at 654 nm. The method has a detection limit (based on 3σ) of 40 ng/L (5 ng/cm²) and an overall extraction efficiency greater than 80% for each surface type (concrete, Plexiglas, glass, steel). Methods to prevent interference by metal ions commonly found on building materials are discussed.     

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.     

Synthesis and evaluation of new propazine-imprinted polymer formats for use as stationary phases in liquid chromatography

Silica particles have been used as supports for the preparation of three different propazine-imprinted polymer formats. First format refers to grafting of thin films of molecularly imprinted polymers (MIPs) using an immobilised iniferter-type initiator (inif-MIP). The other two new formats were obtained by complete filling of the silica pores with the appropriate polymerisation mixture leading to a silica-MIP composite material (c-MIP) followed by the dissolution of the silica matrix resulting in spherical MIP beads (dis-MIP). These techniques offer a mean of fine-tuning the particle morphology of the resulting MIP particles leading to enhanced capacity in chromatographic applications. Porous silica (specific surface area S = 380 m² g⁻¹, particle size p_s = 10 μm, pore volume V_p = 1.083 ml g⁻¹ and pore diameter d_p = 10.5 nm), methacrylic acid and ethylenglycol dimethacrylate were used for the preparation of the materials. All the MIP formats imprinted with propazine have been characterised by elemental analysis, FT-IR spectroscopy, nitrogen adsorption and scanning electron microscopy. Further, the materials were assessed as stationary phases in HPLC. Capacity factors, imprinting factors and theoretical plate numbers were calculated for propazine and other related triazines in order to compare the chromatographic properties of the three different stationary phases. For the inif-MIPs the column efficiency depended strongly on the amount of grafted polymer. Thus, only the polymers grafted as thin films of ca. 1.3 nm average thickness show imprinting effects and the highest column efficiency giving plate numbers (N) of 1600 m⁻¹ for the imprinted propazine. The performance of the c-MIP stationary phase decreases as result of the complete pore filling after polymerisation and increases again after the removal of the silica matrix due to a better mass transfer in the porous mirror-image resulting polymer. From this study can be concluded that the inif-MIP shows the best efficiency for use as stationary phase in HPLC for the separation of triazinic herbicides.     

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.     

Selective extraction of U(VI), Th(IV), and La(III) from acidic matrix solutions and environmental samples using chemically modified Amberlite XAD-16 resin

A new grafted polymer has been developed by the chemical modification of Amberlite XAD-16 (AXAD-16) polymeric matrix with [(2-dihydroxyarsinoylphenylamino)methyl]phosphonic acid (AXAD-16-AsP). The modified polymer was characterized by a combination of ¹³C CPMAS and ³¹P solid-state NMR, Fourier transform-NIR-FIR-Raman spectroscopy, CHNPS elemental analysis, and thermogravimetric analysis (TGA). The distribution studies for the extraction of U(VI), Th(IV), and La(III) from acidic solutions were performed using an AXAD-16-AsP-packed chromatographic column. The influences of various physiochemical parameters on analyte recovery were optimized by both static and dynamic methods. Accordingly, even under high acidities (>4 M), good distribution ratio (D) values (10²–10⁴) were achieved for all the analytes. Metal ion desorption was effective using 1 mol L^–1 (NH₄)₂CO₃. From kinetic studies, a time duration of <15 min was sufficient for complete metal ion saturation of the resin phase. The maximum metal sorption capacities were found to be 0.25, 0.13, and 1.49 mmol g^–1 for U(VI); 0.47, 0.39, and 1.40 mmol g^–1 for Th(IV); and 1.44, 1.48, and 1.12 mmol g^–1 for La(III), in the presence of 2 mol L^–1 HNO₃, 2 mol L^–1 HCl, and under pH conditions, respectively. The analyte selectivity of the grafted polymer was tested in terms of interfering species tolerance studies. The system showed an enrichment factor of 365, 300, and 270 for U(VI), Th(IV), and La(III), and the limit of analyte detection was in the range of 18–23 ng mL^–1. The practical applicability of the polymer was tested with synthetic nuclear spent fuel and seawater mixtures, natural water, and geological samples. The RSD of the total analytical procedure was within 4.9%, thus confirming the reliability of the developed method.     

Ligandless cloud point extraction of Cr(III), Pb(II), Cu(II), Ni(II), Bi(III), and Cd(II) ions in environmental samples with Tween 80 and flame atomic absorption spectrometric determination

A cloud point extraction (CPE) procedure has been developed for the determination trace amounts of Cr(III), Pb(II), Cu(II), Ni(II), Bi(III), and Cd(II) ions by using flame atomic absorption spectrometry. The proposed cloud point extraction method was based on cloud point extraction of analyte metal ions without ligand using Tween 80 as surfactant. The surfactant-rich phase was dissolved with 1.0 mL 1.0 mol L⁻¹ HNO₃ in methanol to decrease the viscosity. The analytical parameters were investigated such as pH, surfactant concentration, incubation temperature, and sample volume, etc. Accuracy of method was checked analysis by reference material and spiked samples. Developed method was applied to several matrices such as water, food and pharmaceutical samples. The detection limits of proposed method were calculated 2.8, 7.2, 0.4, 1.1, 0.8 and 1.7 μg L⁻¹ for Cr(III), Pb(II), Cu(II), Ni(II), Bi(III), and Cd(II), respectively.     

Solid-phase extraction of iron(III) with an ion-imprinted functionalized silica gel sorbent prepared by a surface imprinting technique

A new Fe(III)-imprinted amino-functionalized silica gel sorbent was prepared by a surface imprinting technique for selective solid-phase extraction (SPE) of Fe(III) prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Compared with non-imprinted polymer particles, the ion-imprinted polymers (IIPs) had higher selectivity and adsorption capacity for Fe(III). The maximum static adsorption capacity of the ion-imprinted and non-imprinted sorbent for Fe(III) was 25.21 and 5.10 mg g⁻¹, respectively. The largest selectivity coefficient of the Fe(III)-imprinted sorbent for Fe(III) in the presence of Cr(III) was over 450. The relatively selective factor (α_r) values of Fe(III)/Cr(III) were 49.9 and 42.4, which were greater than 1. The distribution ratio (D) values of Fe(III)-imprinted polymers for Fe(III) were greatly larger than that for Cr(III). The detection limit (3σ) was 0.34 μg L⁻¹. The relative standard deviation of the method was 1.50% for eight replicate determinations. The method was validated by analyzing two certified reference materials (GBW 08301 and GBW 08303), the results obtained is in good agreement with standard values. The developed method was also successfully applied to the determination of trace iron in plants and water samples with satisfactory results.     

Chemical speciation of chromium(III,VI) employing extractive spectrophotometry and tetraphenylarsonium chloride or tetraphenylphosphonium bromide as ion-pair reagent

A simple and accurate extractive spectrophotometric procedure for the chemical speciation of chromium(III,VI) species in aqueous media has been developed. The method is based upon the extraction of the complex ion-associate formed between the chloro chromate (CrO₃Cl⁻) anion and the ion-pair reagent tetraphenylarsonium chloride (TPAs⁺Cl⁻) or tetraphenylphosphonium bromide (TPP⁺Br⁻) at pH ≤ 0 in chloroform followed by direct spectrophotometric measurement at 355 nm. The optimum concentration range evaluated by Beer-Lambert's law, Ringbom's plot, the molar absorptivity, the Sandell's sensitivity, the extraction and stability constants (K_D, K_ex and β), the stoichiometry and the extraction equilibria of the produced complex ion-associates have been determined and gave a convenient applications of the investigated system for analytical purposes. Chromium(III) was also determined by the proposed procedure after prior oxidation to chromate with H₂O₂ in alkaline solution. The method has been applied successfully for the analysis of chromium(VI) and total chromium(III,VI) in industrial wastewater of electroplating plant.     

Imprinted polymer particles for selenium uptake: synthesis, characterization and analytical applications

This work reports the preparation of molecularly imprinted polymer (MIP) particles for selective extraction and determination of selenium ions from aqueous media. Polymerization was achieved in a glass tube containing SeO₂, o-phenylenediamine, 2-vinylpyridine (VP), ethyleneglycoldimethacrylate (EDMA), 2,2′-azobisisobutyronitrile (AIBN). The polymer block obtained was ground and sieved (55-75 μm) and the Se-o-phenylenediamine complex was removed from polymer particles by leaching with 2 M of HCl, which leaves a cavity in the polymer particles. The polymer particles both prior to and after leaching have been characterized by IR and thermogravimetric (TG) studies. The effect of different parameters, such as pH, extraction time, type and least amount of eluent for elution of complex from polymer were evaluated. Extraction efficiencies >99% were obtained by elution of the polymers with 15 mL of methanol-acetonitrile mixture (1:2, v/v). The limit of detection of the proposed method followed by hydride generation atomic absorption spectroscopy (HG-AAS) was found to be 3.3 μg L⁻¹ and a dynamic linear range (DLR) of 10-200 μg L⁻¹ was obtained. The relative standard deviations (R.S.D.s) at 30.0 μg L⁻¹ of Se were below than 8.1%. The influence of various cationic interferences on percent recovery of complex was studied. The method was applied to the recovery and determination of selenium in different real samples.     

Conformational study of lanthanide(III) complexes of N-(2-salicylaldiminatobenzyl)-1-aza-18-crown-6 by using X-ray and ab initio methods

A structural study of lanthanide complexes with the deprotonated form of the monobracchial lariat ether N-2-salicylaldiminatobenzyl-aza-18-crown-6 (L⁴) (Ln = La(III)–Tb(III)) is presented. Attempts to isolate complexes of the heaviest members of the lanthanide series were unsuccessful. The X-ray crystal structures of [Pr(L⁴)(H₂O)](ClO₄)₂ · H₂O · C₃H₈O and [Sm(L⁴)(H₂O)](ClO₄)₂ · C₃H₈O show the metal ion being bound to the eight donor atoms of the ligand backbone. Coordination number nine is completed by the oxygen atom of an inner-sphere water molecule. Two different conformations of the crown moiety (labelled as A and B) are observed in the solid state structure of the Pr(III) complex, while for the Sm(III) complex only conformation A is observed. The complexes were also characterized by means of theoretical calculations performed in vacuo at the HF level, by using the 3-21G^∗ basis set for the ligand atoms and a 46 + 4fⁿ effective core potential for lanthanides. The optimized geometries of the Pr(III) and Sm(III) complexes show an excellent agreement with the experimental structures obtained from X-ray diffraction studies. The calculated relative energies of the A and B conformations for the different [Ln(L⁴)(H₂O)]²⁺ complexes (Ln = La, Pr, Sm, Ho or Lu) indicate a progressive stabilization of the A conformation with respect to the B one upon decreasing the ionic radius of the Ln(III) ion. For the [Ln(L⁴)(H₂O)]²⁺ systems, most of the calculated bond distances between the metal ion and the coordinated donor atoms decrease along the lanthanide series, as usually observed for Ln(III) complexes. However, our ab initio calculations provide geometries in which the Ln–O(5) bond distance [O(5) is an oxygen atom of the crown moiety] increases across the lanthanide series from Sm(III) to Lu(III).