Radiometric determination of uranium in natural waters after enrichment and separation by cation-exchange and liquid-liquid extraction

Preconcentration of uranium from natural water samples using Chelex-100 cation-exchange resin, its selective extraction by tributylphosphate and electrodeposition on stainless steel discs is reported. The validity of the separation procedure and the chemical recoveries were checked by addition of uranium standard solution as well as by tracing with ²³²U. The average uranium yield for the cation-exchange was (97±2)%, for the liquid-liquid extraction was (95±2)% and for the electrodeposition was more than 99%. Employing high-resolution a-spectroscopy, the measured activity of ²³⁸U and ²³⁴U radioisotopes was found to be ~7 mBq^.l^-1 and ~35 mBq^.l^-1 for ground- and seawater samples, respectively. The energy resolution (FWHM) of the α-peaks was 22 keV, the minimum detectable activity (MDA) was estimated to be 1 mBq^.l^-1 (at 95% confidence limit). This revised version was published online in July 2006 with corrections to the Cover Date.     

Speciation of hexavalent chromium in waters by liquid-liquid extraction and GFAAS determination

Diperoxo chromium oxide is produced by reaction of hydrogen peroxide on chromium(VI). Diperoxo chromium creates a complex with ethyl acetate, while chromium(III) remains in an unchanged form in the aqueous phase. By this means chromium(VI) can be extracted into ethyl acetate from the aqueous phase. The optimal conditions of Cr(III)-Cr(VI) separation, as well as the chromium content of the ethyl acetate phase were determined with graphite furnace atomic absorption spectrometry. In the second extraction of Cr(VI) from ethyl acetate back into water phase an additional preconcentration of chromium(VI) can be carried out. The detection limit (3σ) of the developed method found to be 200 ng dm^− 3 for the first extraction and 50 ng dm^− 3 after using the twofold extraction. In consequence of the matrix free ethyl acetate phase after the first extraction, with this separation a really extensive preconcentration of chromium(VI) can be realized.     

Determination of endosulfan and some pyrethroids in waters by micro liquid-liquid extraction and GC-MS

A simple, rapid and reproducible method for the determination of some pesticide residues in water was developed using micro liquid-liquid extraction and gas chromatography - mass spectrometry with selected ion monitoring (GC/MS-SIM). The chlorinated insecticides α- and β-endosulfan and endosulfan-sulfate as well as the synthetic pyrethroids bifenthrin, permethrin, cypermethrin, fenvalerate and deltamethrin can be separated from a 500 mL sample water extracted with 0.5 mL of n-hexane containing anthracene-d₁₀ as internal standard without clean-up in only 13 min. The recovery efficiencies of the tested compounds yielded more than 93.0% at a fortification level of 5 ng mL^–1 and their relative standard deviations were between 1.9 and 11.7%. Detection limit of each compound ranged between 3 and 35 pg mL^–1. The method was applied to ground, sea and tap waters from Almería (Spain). The solubilities in water at 20°?C were determined.     

Determination of endosulfan and some pyrethroids in waters by micro liquid-liquid extraction and GC-MS

A simple, rapid and reproducible method for the determination of some pesticide residues in water was developed using micro liquid-liquid extraction and gas chromatography - mass spectrometry with selected ion monitoring (GC/MS-SIM). The chlorinated insecticides α- and β-endosulfan and endosulfan-sulfate as well as the synthetic pyrethroids bifenthrin, permethrin, cypermethrin, fenvalerate and deltamethrin can be separated from a 500 mL sample water extracted with 0.5 mL of n-hexane containing anthracene-d₁₀ as internal standard without clean-up in only 13 min. The recovery efficiencies of the tested compounds yielded more than 93.0% at a fortification level of 5 ng mL^–1 and their relative standard deviations were between 1.9 and 11.7%. Detection limit of each compound ranged between 3 and 35 pg mL^–1. The method was applied to ground, sea and tap waters from Almería (Spain). The solubilities in water at 20° C were determined. Received: 21 March 1997 / Revised: 28 July 1997 / Accepted: 18 August 1997     

Multivariate optimization of a liquid-liquid extraction of the EPA-PAHs from natural contaminated waters prior to determination by liquid chromatography with fluorescence detection

This paper reports the multivariate optimization of a liquid–liquid extraction procedure for the determination of 15 EPA-polycyclic aromatic hydrocarbons (PAHs) by high-performance liquid chromatography with fluorescence detection. A Doehlert design was used to find optimum conditions for the procedure through Response Surface Methodology. Three variables (total volume of hexane, number of extraction steps and duration of such steps) were elected as factors in the optimization study. A principal component analysis (PCA) was run with optimized data, resulting in four groups of PAHs, ordered according to their molecular weight. Final working conditions were established in order to achieve a more robust methodology in relation to all fifteen PAHs under study. Best results could be observed when 77 mL of hexane were divided in four consecutive extraction steps with 18 min each. These experimental conditions were applied in the analysis of a spiked river water sample, and the recoveries varied between 80.9 and 106%, with an average value of 97.1 ± 6.8%. The application of the methodology to river water showed that the method has a good average precision for the studied PAHs.     

Cloud-point extraction of nodularin-R from natural waters

A cloud-point extraction (CPE) technique for the determination of a cyanobacterial hepatotoxin, nodularin-R, in aqueous media using a cationic surfactant, tricaprylmethylammonium chloride (Aliquat-336), was developed. Cloud-point phase separation of Aliquat-336 at ambient temperature was induced by the addition of sodium sulfate. The Aliquat-336/Na₂SO₄ CPE system displayed large preconcentration factor, F_C, for nodularin-R. At the operational CPE conditions, F_C of 709.2 was achieved. Distribution constant, K_D, of the distribution of nodularin-R between the surfactant-rich and aqueous phases of the CPE system was estimated to be (4.94±0.8)×10³. Coupled to liquid chromatography with UV detection, the CPE method offered a detection limit of 330 pg ml⁻¹ (in freshwater)/1.3 ng ml⁻¹ (in seawater) and a repeatability of 6.4% (in freshwater) (n=7, P<0.05) for nodularin-R in a sample of 25 ml. The CPE is a rapid process and no cleanup step is required. Effects of pH, natural abundant anion (chloride) and dissolved organic matters (DOM, humic acid, HA) on the extraction efficiency were evaluated. A double CPE technique was developed to overcome interferences encountered in the analysis of environmental samples. Applicability of the new method to the determination of nodularin-R in real coastal marine water samples has also been demonstrated.     

On-line liquid-liquid extraction system using a new phase separator for flame atomic absorption spectrometric determination of ultra-trace cadmium in natural waters

A robust flow injection (FI) on-line liquid-liquid extraction (LLE) preconcentration/separation system associated with a newly designed gravitational phase separator, coupled to flame atomic absorption spectrometry (FAAS) was developed. The performance of the system was illustrated for cadmium determination at the μg l⁻¹ level. The non-charged cadmium complex with ammonium pyrrolidine dithiocarbamate (APDC) was extracted on-line into isobutyl methyl ketone (IBMK). The organic phase was effectively separated from a large volume of aqueous phase and is led into a 100 μl loop of an injection valve before its introduction into the nebulizer. The system was optimized and offered good performance characteristics with unlimited life time of phase separator, greater flow rate ratios and improved flexibility, as compared with other solvent extraction preconcentration systems. With a sampling frequency of 33 h⁻¹, the enhancement factor was 155, the detection limit was 0.02 μg l⁻¹, the relative standard deviation was 3.2% at 2.0 μg l⁻¹ Cd concentration level and the calibration curve was linear over the concentration range 0.06-6.0 μg l⁻¹. The accuracy of the proposed method was evaluated by analyzing a certified reference material of water and by recovery measurements on spiked samples. Finally, it was successfully applied to the analysis of tapwater, river and seawater samples.     

A liquid-liquid distribution method for the study of complexation of cadmium in natural waters

Liquid-liquid distribution of cadmium between pyridine solution in benzene and aqueous phase containing iodide has been radiometrically investigated, in order to develop a simple method for the study of complexation of cadmium in aqueous solutions. The degree of complexation of cadmium can be determined from the decrease of the distribution ratio in the presence of complexing agents forming non-extractable complexes with this metal. The method was verified for the determination of the composition and stability constants of cadmium with acetate, tartrate, oxalate and glycolate anions and applied for the study of complexation of cadmium in natural waters.     

Chiral separation by enantioselective liquid-liquid extraction

The literature on enantioselective liquid-liquid extraction (ELLE) spans more than half a century of research. Nonetheless, a comprehensive overview has not appeared during the past few decades. Enantioselective liquid-liquid extraction is a technology of interest for a wide range of chemists and chemical engineers in the fields of fine chemicals, pharmaceuticals, agrochemicals, fragrances and foods. In this review the principles and advances of resolution through enantioselective liquid-liquid extraction are discussed, starting with an introduction on the principles of enantioselective liquid-liquid extraction including host-guest chemistry, extraction and phase transfer mechanisms, and multistage liquid-liquid extraction processing. Then the literature on enantioselective liquid-liquid extraction systems is reviewed, structured on extractant classes. The following extractant classes are considered: crown ether based extractants, metal complexes and metalloids, extractants based on tartrates, and a final section with all other types of chiral extractants.     

Determination of organotins in natural waters by toluene extraction and graphite furnace AAS

The determination of tributyltin in natural waters by extraction into toluene and graphite-furnace AAS measurement of tin has been investigated. The effect of pH on the extraction of mono-, di- and tributyltin and triphenyltin has been examined and the optimum conditions for the estimation of tributyltin assessed. The AAS performance is greatly improved by using furnace tubes pretreated by soaking in sodium tungstate solution. Such pretreatment is essential if low detection limits are to be attained. Extraction of the tributyltin from aqueous media resulted in a marked signal enhancement (irrespective of the type of furnace tube), which varied according to the nature of the aqueous solution. The enhancement is believed to result from water in the toluene extract activating the tube surface. Methods for the estimation of tributyltin in waters, appropriate for screening samples as part of routine monitoring programmes, are described. With a 1-litre sample, a limit of detection of approximately 4 ng/l. was attained for tin. The relative standard deviation of six replicate analyses of sea-water containing 170 ng/l. tin (present as tributyltin) was 1.5%.     

Characterization of N-palmitoylated human growth hormone by in situ liquid-liquid extraction and MALDI tandem mass spectrometry

Acylation is a common post-translational modification found in secreted proteins and membrane-associated proteins, including signal transducing and regulatory proteins. Acylation is also explored in the pharmaceutical and biotechnology industry to increase the stability and lifetime of protein-based products. The presence of acyl moieties in proteins and peptides affects the physico-chemical properties of these species, thereby modulating protein stability, function, localization and molecular interactions. Characterization of protein acylation is a challenging analytical task, which includes the precise definition of the acylation sites in proteins and determination of the identity and molecular heterogeneity of the acyl moiety at each individual site. In this study, we generated a chemically modified human growth hormone (hGH) by incorporation of a palmitoyl moiety on the N(epsilon) group of a lysine residue. Monoacylation of the hGH protein was confirmed by determination of the intact molecular weight by mass spectrometry. Detailed analysis of protein acylation was achieved by analysis of peptides derived from hGH by protease treatment. However, peptide mass mapping by MALDI MS using trypsin and AspN proteases and standard sample preparation methods did not reveal any palmitoylated peptides. In contrast, in situ liquid-liquid extraction (LLE) performed directly on the MALDI MS metal target enabled detection of acylated peptide candidates by MALDI MS and demonstrated that hGH was N-palmitoylated at multiple lysine residues. MALDI MS and MS/MS analysis of the modified peptides mapped the N-palmitoylation sites to Lys158, Lys172 and Lys140 or Lys145. This study demonstrates the utility of LLE/MALDI MS/MS for mapping and characterization of acylation sites in proteins and peptides and the importance of optimizing sample preparation methods for mass spectrometry-based determination of substoichiometric, multi-site protein modifications.     

Determination of ultratrace elements in natural waters by solid-phase extraction and atomic spectrometry methods

A study was carried out on the preconcentration of ultratrace amounts of cadmium, lead, manganese, copper and iron from high-salinity aqueous samples and determination by atomic spectrometry methods. Sample volume, amount of resin, loading flow rate, and elution volume were optimized in order to obtain the simultaneous preconcentration of all the analytes. Quantitative recoveries were obtained by using 200 mg of iminodiacetic resin with a loading flow rate of 2 mL min(-1), elution volume of 3 mL and sample volume of 50-450 mL. Only copper in seawater samples was not completely retained by the resin (60-70% recovery), due to unfavorable competition of iminodiacetic-active groups with organically bound metal.To quantify the metals in the eluates, two atomic spectrometry techniques were compared: electrothermal atomization atomic absorption spectrometry (ETAAS) and inductively coupled plasma-optical emission spectrometry (ICP-OES) with simultaneous CCD detection system. Both techniques are suitable for sample analysis with detection limits of 1.0, 4.7, 3.3, 6.8, and 53 ng L(-1) using ETAAS and 12, 122, 3.4, 17, and 21 ng L(-1) using ICP-OES for Cd, Pb, Mn, Cu, and Fe, respectively. Relative standard deviations of the procedures ranged from 1.7 to 14% at the sub-microg L(-1) concentration level. The accuracy of both methods was verified by analyzing various certified reference materials (river water, estuarine water, coastal and off-shore seawater).     

Evaluation of micromolar compleximetric titrations for the determination of the complexing capacity of natural waters

The titration of micromolar levels of complexing agents with metal ion titrants, and voltammetric methods to locate the equivalence point, has been evaluated experimentally and theoretically. Both anodic stripping voltammetry and differential pulse polarography give systematically low results if labile metal ions are used as titrants. Low-temperature (0 °C) dual-cell anodic stripping voltammetry greatly minimizes the effects of metal complex lability but the mercury film electrodes deteriorate rapidly because of temperature cycling. A micromolar compleximetric titration with a voltammetric end-point is not a practical method for determining the complexing capacity of natural waters.     

工业含铬废水的络合萃取处理工艺研究

采用络合萃取法处理工业含铬废水,考察了起始pH、流速和接触时间等对络合萃取处理效果的影响,探讨了铬盐生产废水和电镀废水的处理工艺。结果表明;在废水起始pH为1.0-2.0时,络合萃取法能方便、快速、有效地去除废水中的六价铬。络合萃取．碱沉淀法适用于六价铬含量远大于三价铬含量的电镀废水的处理,氧化．络合萃取法可用于三价铬含量较高的电镀废水的处理。采用两级处理能使高浓度铬盐生产废水的出水达到国家排放标准。     

Preconcentration in multistage liquid-liquid extraction

Theoretical possibilities of the preconcentration of solutes in multistage static liquid-liquid extraction have been investigated. It was found that the preconcentration increases with increasing distribution ratio of the solutes between two phases as well as with the number of stages (n) and reaches its maximum value for n approaching infinity, i.e., in dynamic extraction. Comparison of the preconcentration in multistage (P_ns) and one-stage (p_1s) static operations shows that the relative preconcentration (q_ns=p_ns/p_1s) increases to infinity as the separation efficiency approaches 100%. Some of these theoretical considerations have been confirmed in extraction of radioiodine from aqueous solutions.Presented at the 2nd International Conference on the Separation of Ionic Solutes, SIS'87, Smolenice, Czechoslovakia, October 12–15, 1987.     

Determination of triazine herbicides in natural waters by solid-phase extraction and non-aqueous capillary zone electrophoresis

Capillary zone electrophoresis (CZE) in an organic medium was used to analyse triazines at sub-ppb concentration levels in natural waters after a preconcentration step using conventional C18 cartridges and new Oasis HLB devices. With both sorbents, satisfactory results were obtained on analysing deionized water. However, on analysing natural waters, both sorbents showed very different types of behaviour. The different variables affecting the elution of both sorbents were studied, resulting in the choice of Oasis HLB as the most suitable for later separation by CZE in non-aqueous medium. Combination of a preconcentration step with electrokinetic injection revealed that capillary electrophoresis with simple UV detection can also be used satisfactorily for the quantification of micropollutants in natural waters. The detection limits obtained varied between 0.01 and 0.05 microg l(-1), depending on the type of matrix analysed. The day-to-day precision varied between 0.9% and 2.3%, expressed as the relative standard deviation.     

Effects of complexing agents in radical copolymerization

Radical copolymerization of methyl methacrylate (MMA, M₁) with various monomers has been studied in presence of modifiers, i.e., complexing agents (CA): ZnCl₂, AlCl₃, AlBr₃, Al(C₂H₅)₂Cl, forming coordinate complexes with ester group of the monomer and of the propagating radical. The comonomers of the first group form complexes of similar structure and stability as MMA, methyl acrylate, or butyl acrylate. The comonomers of the second group do not form complexes with the modifiers (vinylidene chloride, 2,6-dichlorostyrene, p-chlorostyrene, styrene). For all systems studied the copolymer composition follows the Mayo-Lewis equation. In the first group of the systems the effective reactivity ratios (r₁, r₂) approach unity with increase of the CA molar content (r₁ = r₂ ? 1 at [(CA)/MMA] + [MA] ≥ 0,3) In the second group of the systems the values of r₁ either increase to a limit value (at [CA]/[MMA] ≥ 0.3), pass through maximum, or decrease to a limiting value with the CA molar content. The values of r₂ decrease in all systems. The character of variation of r₁ and r₂ has been explained in terms of effects of the CA's on reactivity of MMA and PMMA radical. The equations for the copolymer compositions in these systems have been derived.     

超声辅助液液萃取法提取烟用香精成分的研究

采用超声辅助液液萃取法(ULLE)提取某品牌烟用香精成分,GC-MS对其进行分析,研究了不同萃取剂、萃取时间和萃取温度对分析结果的影响,初步确定了最佳条件为:以二氯甲烷为萃取剂,饱和NaCl溶液作水相,室温下超声萃取5 min.又分别与同时蒸馏萃取法(SDE)和传统的液液萃取法(LLE)作以比较,对ULLE法和SDE法鉴定出的化学成分、重现性和定量值进行了对比.结果表明:超声辅助液液萃取具有操作简便、快速、节能、萃取效率高、重现性好等特点,适合于烟用香精成分的提取.     

Application of chemometric assisted dispersive liquid-liquid microextraction to the determination of personal care products in natural waters

A rapid and simple method for the determination of two phthalates and five polycyclic musks in water samples using dispersive liquid-liquid microextraction (DLLME) mated to chemometrics and coupled to GC-MS was developed. Volume of extraction (CCl₄) and disperser solvent (MeOH), pH, ionic strength, extraction time, centrifugation time as well as centrifugation speed were optimized in a 2^7-4 Plackett-Burman design. The obtained significant factors were optimized by using a central composite design (CCD) and the quadratic model between the dependent and the independent variables was built. The optimum experimental conditions of the proposed method were: 250 μL carbon tetrachloride, 0.62 mL methanol, 7.5 min centrifugation time, natural pH containing 0% (w/v) NaCl, while keeping centrifugation speed fixed at 4000 rpm.The calculated calibration curves gave high-level linearity for all target analytes with correlation coefficients ranging between 0.9970 and 0.9992. The repeatability and reproducibility of the proposed method, expressed as relative standard deviation, varied between 2.6% to 9.7% and 5.7% to 12.2%, respectively. The obtained LOD values were in the range of 8-63 ng L⁻¹.