Selectivity in the coextraction of cation and anion by electrochemically modulated liquid-liquid extraction

Electrochemistry at the interface between two immiscible electrolyte solutions has been presented as a method of electrochemically modulated liquid-liquid extraction, where ions in a mixture can be selectively partitioned as a function of the applied interfacial potential difference. In this study, a mixture comprising 4-octylbenzenesulfonate (4-OBSA-) and tetraethylammonium (TEA+) ions was evaluated. The application of negative potential differences enabled the selective extraction of 4-OBSA- into the organic phase, and more positive potential differences enabled the selective extraction of TEA+. However, intermediate potentials lead to the coextraction of both ions into the organic phase, with apparent selectivity for TEA+ over 4-OBSA-. An increased concentration of either ion in the mixture inhibited the extraction response of the other ion, but the order of the extraction at these intermediate potentials was always TEA+ followed by 4-OBSA-. The reasons for the selectivity for the cation over the anion are discussed.     

Enhancement of CsNO3 extraction in 1,2-dichloroethane by tris(2-aminoethyl)amine triamide derivatives via a dual-host strategy

A systematic study of a dual-host system exhibiting pairwise anion/cation separations has been performed for CsNO3 extraction. Tripodal triamides 1-4 and 9 derived from condensation of hexanoic (for 1), octanoic (for 2), decanoic (for 3), lauric (for 4), and p-tert-butylbenzoic (for 9) acid with tris(2-aminoethyl)amine (tren) were used together with tetrabenzo-24-crown-8, a well-known Cs+ cation receptor. By using 5 mM crown ether in the organic phase and 10 mM CsNO3 with 0.1 mM HNO3 in the aqueous phase, tripods 1, 2, and 9 enhance CsNO3 extraction by factors of 2.4, 1.7, and 4.4, respectively (for 50 mM amide concentration), while the corresponding monoamide controls 5-8 derived from n-propylamine (5, 6) or N,N'-dimethylethylenediamine (7, 8) and hexanoic (5, 7) or octanoic (6, 8) acid derivatives gave no significant enhancement under the same conditions. This behavior may be ascribed to nitrate complexation by the triamides, which lowers the overall thermodynamic barrier for the salt transfer to the organic phase. The nitrate binding was confirmed by 1H NMR titration of receptor solutions, using tetrabutylammonium nitrate. Association constants for the formation of the anion-nitrate complexes were found to vary between 33 and 52 M-1 for the more soluble triamides. The synergistic effects for CsNO3 extraction are in reasonable agreement with the values predicted theoretically from the measured association constants. Electrospray ionization mass spectrometry confirmed the predominant formation of 1:1 tripod-nitrate complexes. Monoamide controls gave no evidence of anion complexation.     

1,3-丙二醇发酵液电渗析脱盐中离子膜影响的实验研究

电渗析法可以有效去除1,3-丙二醇发酵液中存在的有机酸盐,保证下游处理过程的顺序进行,为了选取适于该脱盐过程的离子膜种类,采用4种离子交换膜分别进行了发酵液电渗析实验,通过对脱盐效果的综合评价着重探讨了离子交换膜性能的影响、实验研究表明,对于有机酸盐电渗析脱除过程,阴膜的选取至关重要;当阴、阳膜导电能力较强时,脱盐效果良好,此外,进行了中性溶质在不同离子膜中的模拟扩散实验,在综合比较脱盐效果和中性溶质扩散损失的基础上,获得了针对1,3-丙二醇发酵液电渗析脱盐的较优阴、阳离子膜种类。     

Kinetic analysis of ion pair extraction of an alkyl sulfate anion across a liquid/liquid interface by fluorescence microspectroscopy and microelectrochemistry of single microdroplets

Mass transfer of an alkyl sulfate anion with a (ferrocenylmethyl)trimethylammonium cation from water into single oil microdroplets was kinetically studied by microcapillary injection, fluorescence microspectroscopy, and microelectrochemistry. The partitioning ratio and the extraction rate significantly depended on the alkyl chain length of the alkyl sulfate anion. The extraction rate for the n-dodecyl sulfate or n-tridecyl sulfate ion was proportional to both the alkyl sulfate ion and ferrocene derivative concentrations while that for the n-undecyl sulfate ion was proportional to the anion concentration alone. The results are discussed in terms of transfer of the individual ions across the microdroplet/water interface and adsorption/ion pair formation of the alkyl sulfate ion at the microdroplet/water interface.     

Improved tert-butyldimethylsilylation gas chromatographic/mass spectrometric detection of nerve gas hydrolysis products from soils by pretreatment of aqueous alkaline extraction and strong anion-exchange solid-phase extraction

In the analysis of tert-butyldimethylsilyl derivatives (IBDMS) of alkyl methylphosphonic acids (RMPA) and methylphosphonic acid (MPA), from soils by gas chromatography/mass spectrometry (GC/MS), the detection yields are generally low, due to the suppression of TBDMS derivatization by the soil matrix components and the adsorption of RMPA and MPA to the soils. An ion-exchange pretreatment of the aqueous soil extract can be used to overcome the former factor by removing interfering compounds. A pretreatment method is described for improving the detection yields due to the latter factor, using an alkaline extraction procedure. The recovery was estimated quantitatively using capillary electrophoresis. The soil samples tested included volcanogenous immature soils and showed a low aqueous extraction recovery and GC/MS detection yields. The inclusion of sodium hydroxide in the extraction solvent dramatically increased the recovery. Using a 0.1 M sodium hydroxide solution, the recovery was in excess of 68%. Interfering components were removed from the alkaline soil extract by solid-phase extraction of the acids on a silica-based strong anion exchanger. The alkaline soil extract was neutralized with hydrofluoric acid and applied to the cartridge in the fluoride form. After washing with water, MPA and RMPA could be eluted with methanolic ammonia nearly quantitatively. Using the established pretreatment method, MPA and RMPA were detected from all the soil samples in more than 67% yield.     

EDTA-directed synthesis of highly active porous titania with bicrystalline framework

Porous titania with bicrystalline (anatase and rutile) framework was successfully synthesized by a facile hydrothermal process using inexpensive and nontoxic organic molecules, EDTA (ethylenediamine-tetra-acetic acid) or its sodium salts as a template, which could be removed from porous titania by the extraction with sodium hydroxide aqueous solution and then easily recovered by acidification. XRD investigation suggested that the ratio of anatase to rutile could be readily tuned by employing different sodium salts of EDTA. All of as-prepared porous titania showed higher activities than the commercial photocatalyst P25 for the degradation of methyl orange (MO), because of the high surface area, bicrystalline phase composition and bimodal porous structures.     

Capillary electrochromatography with fused-silica capillaries packed with copolymeric reversed-phase adsorbent and ion exchangers

Macroporous poly(styrene-divinylbenzene) (PSDVB), PRP-1, a reversed-phase adsorbent, and PSDVB-based strong acid cation exchangers and strong base and weak base anion exchangers were evaluated as stationary phases for capillary electrochromatography (CEC). Electroosmotic flow (EOF) for adsorbent and exchanger packed fused-silica capillaries for acetone as the marker increases with increasing ion exchange capacity, buffer organic solvent concentration, and applied voltage, is nearly independent of pH, and decreases with increased buffer ionic strength. For anion exchangers, EOF is reversed. Thiourea, acetone, acrylamide, nitromethane, propanal, and acetic acid were evaluated as EOF markers and undergo weak interaction with the PSDVB-based stationary phases. EOF in a basic buffer is greater than or equal to silica-based C-18 and cation exchanger packed capillaries. For an acidic buffer, EOF for a PRP-1 capillary is almost twice the C-18 packed capillary. As analyte hydrophobicity increases, retention and migration time increases for the PSDVB-based stationary phases. As exchange capacity increases, availability of the polymeric matrix for analyte partitioning decreases, causing analyte migration time to decrease. Increasing buffer organic solvent concentration decreases analyte retention. The PSDVB-based stationary phases provide good resolving power and reproducibility and are applicable to the CEC separation of neutral, weakly acidic, and basic analytes. Efficiency, however, is less than obtained with silica-based stationary phases. Because of stability in a strong acid buffer, the CEC separation of weak acids, where dissociation is suppressed, and weak bases as cations is possible. Separations of short-chain alkyl aldehydes, methyl ketones, aromatic hydrocarbons, substituted benzene derivatives, and short-chain carboxylic acids are described.     

Extraction of phenol by sulfuric acid salts of trioctylamine

Abstract

The extraction of phenol from an aqueous solution using sulfuric acid salts of trioctylamine (TOA salts) was carried out. Trioctylamine (TOA) dissolved in diisopropyl ether (DIPE) (or 1‐octanol, cyclohex‐ane, benzene and kerosene) was evaluated for extraction of phenol at various volume ratios of organic phase to aqueous phase at varied temperatures. The equilibrium distribution coefficient (K_D ) for the extraction of phenol with TOA salts in those diluents was measured. Phenol is extracted by a physical distribution with pure diluent alone and through the interaction between TOA and phenol. The latter was quantitatively interpreted according to a reaction scheme in which adducts of several kinds were composed of trioctylamine and phenol. The TOA salts have a significantly greater extraction capability for phenol than TOA itself. The reaction of phenol and hydroxide ion to form phenoxide ion is used to explain the small extraction of solute at high pH. A simple mathematical model was derived to account for the effect of the volume ratio of organic phase to aqueous phase on the value of K_D, and for the effect of the initial concentration of phenol on the value of K_D.     

碱性染料与磷钨酸形成的新型电荷转移盐的制备与表征

报道了用Keggin结构的磷钨酸与碱性染料结晶紫、碱性藏红T和碱性湖兰BB反应形成的3种新型电荷转移盐。利用元素分析、差热-热重、变温红外、固体漫反射电子光谱对标题化合物的组成、热稳定性和光学性质进行了表征。     

Effect of the phase volume ratio on the potential of a liquid-membrane ion-selective electrode

Two-phase liquid system IA(w)|IX(o) comprising the interface between the aqueous solution (w) of uni-univalent electrolyte IA and an organic solvent solution (o) of a uni-univalent electrolyte IX with the common cation I(+) is considered as a simple model of a liquid-membrane ion-selective electrode (ISE). Taking into account the electroneutrality and mass balance conditions, the equilibrium Galvani potential difference (pd) between the aqueous and organic phases, phi = phi(w) - phi(o), is calculated numerically as a function of the ratio of the initial electrolyte concentrations, x = / = 10(-)(4)-10(4), for the selected values of the phase volume ratio r = V(o)/V(w) = 10(-)(3), 1, and 10(3), and the standard ion transfer potentials of the present ions ranging from -0.5 to 0.5 V. Numeric results corroborate the symbolic expressions derived for the cases when X(-) and A(-) are extremely lipophilic and hydrophilic ions, respectively, or when the concentration ratio x is extremely large or small. In contrast to the extraction system, where both electrolytes are initially present in the aqueous phase, the effect of the phase volume ratio on the equilibrium pd in the ISE model is rather weak, unless the counterions X(-) and A(-) differ little in their lipophilicity from the target ion I(+). It is shown that both the ISE and extraction model exhibit the Nernstian behavior only in a limited range of the concentration ratio x depending on the value of the standard ion transfer potentials of the counterions. When this ratio is extremely large or small, equilibrium pd approaches the limiting value given by the distribution potential of the electrolyte IA or IX, respectively. Similar conclusions can be drawn for the two-phase liquid system AI(w)|XI(o) with the common anion I(-).     

Fluorinated nucleogenic phenyl cations and nuclear-chemical route to previously unknown heterocyclic derivatives

A new reactive species, fluorinated phenyl cation generated by β-decay of tritium in difluoroditritiobenzene, was used for introducing fluorinated phenyl fragment into organic compounds. Studies of ion–molecule reactions have shown that, similarly to the unsubstituted nucleogenic phenyl cation, p-difluorophenyl cation directly phenylates the N atom in the heterocyclic ring of quinoline. The nuclear-chemical method allows not only generation of nucleogenic species of various structures, but also one-step synthesis of previously unknown and difficultly accessible heterocyclic derivatives labeled with tritium.     

Nonmolecular solvents in separation methods: dual nature of room temperature ionic liquids

Room temperature ionic liquids (RTIL) are molten salts starting to be used as nonmolecular solvents in separation methods mainly for their extremely low vapor pressure and thermal stability. RTILs are formed by an anion associated to a cation. This intrinsic structure gives them a dual nature. When used as additives in RPLC mobile phases to enhance basic compound separation, RTILs lose their particular physicochemical properties to become just salts. However, a given RTIL is not equivalent to another one made with the same cation. It is shown that both the anion and the cation contribute to solute retention and peak efficiency extending beyond simple "salting-out" or ion-pairing effects. Nine different alkyl-methyl-imidazolium ionic liquids with different alkyl chain length and chloride or BF(4-) or PF(6-) anions were used as additives (50 mM max. conc.) in the liquid chromatography separation of some cationic basic solutes on a Kromasil C18 column. It is shown with sodium salts and an acetonitrile-water 30/70 v/v mobile phase that anions can adsorb on the stationary phase surface according to their lyotropic character. They can also form ion pairs with the cationic basic solutes. Alkyl-imidazolium cations also adsorb on the C18 bonded stationary phase due to hydrophobic character depending on their alkyl chain length. Anion adsorption dramatically increases the cationic solute retention factors when cation adsorption decreases them. The cation adsorption is mainly responsible for peak shape and efficiency enhancements. RTILs are additives that enhance the basic cationic solute peak shape changing peak position. A wise choice of the appropriate combination of anion lyotropy with imidazolium cation hydrophobicity allows playing with solute selectivity and analysis duration.     

Thermodynamic studies on cobalt extraction by 2-heptyl-2-methylnonanoic acid in benzene from chloride solutions

Solvent extraction of Co(II) from aqueous chloride solutions of constant ionic strength (I = 1 M) with a long-chain fatty acid, 2-heptyl-2-methylnonanoic acid (HA), in benzene was studied at four temperatures: 278, 288, 298, and 313 ± 1 K. The influence of various parameters on the extraction equilibrium was studied. The effect of mixing HA with TBP in benzene on the extraction process was examined, and a synergistic effect was revealed. The stoichiometry of the extraction equilibria was determined, and the thermodynamic studies were made for both extraction systems. The thermodynamic functions ΔG ⁰, ΔH ⁰, and ΔS ⁰ were calculated, and the related data were discussed.     

Spatial and spectral imaging of single micrometer-sized solvent cast fluorescent plasticized poly(vinyl chloride) sensing particles

Microscale plasticized PVC particles doped with hydrophobic ionophores are prepared by solvent evaporation of aqueous suspensions of sensing cocktails (poly(vinyl chloride), plasticizer, active sensing components, and tetrahydrofuran) and tested as particulate microoptical sensors. The particles contain either only the chromoionophore ETH 2458 as active reagent or the potassium ionophore BME-44, chromoionophore ETH 5294, and lipophilic anionic sites NaTFPB. The former system functions according to an anion-hydrogen ion coextraction mechanism and shows a Hofmeister anion selectivity pattern, while the latter sensor containing additional ionophores represents the more complex, truly selective optical sensors based on ion-exchange equilibria. Single microspheres are simultaneously characterized spatially and spectrally by fluorescence microscopy, coupled to a spectrometer equipped with a CCD detector. The results indicate that these microspheres respond in complete analogy to traditional thin-film-based optodes previously reported in the literature. The introduction of small, spherical ionophore-based sensing particles that operate on the basis of bulk extraction principles holds the promise of significantly expanding the available chemical palette of microsphere-based analytical assays.     

Specific ion effects on the properties of cationic Gemini surfactant monolayers

The effects of some anions of the Hofmeister series and different divalent cations of alkaline earth metals on the properties of Langmuir monolayers of the cationic Gemini surfactant ethyl-bis (dimethyl octadecylammonium bromide) have been investigated. Surface pressure and potential isotherms at the air-water interface were obtained on aqueous subphases containing sodium salts with several anions of the Hofmeister series (Cl⁻, NO₃⁻, Br⁻, I⁻, ClO₄⁻, and SCN⁻). The influence of the investigated anions on the monolayer properties can be ordered according to the Hofmeister series with a change in the order between bromide and nitrate anions. On the other hand, for a given anion, the cation of the salt also influences the surface properties of the Langmuir films. The monolayers can be transferred onto mica by the Langmuir-Blodgett technique and then the Langmuir-Blodgett films were characterized by atomic force microscopy (AFM). The AFM images show that the molecules become more closely packed and nearly vertical to the surface when anions screen the electric charge of the surfactant molecules.     

On-chip integration of sequential ion-sensing system based on intermittent reagent pumping and formation of two-layer flow

A sequential ion-sensing system using a single microchip was successfully realized. The system developed here involves intermittent pumping of plural organic phases into a microchannel, followed by contact with a single aqueous phase to form a stable organic-aqueous two-layer flow inside the microchannel. Because the plural organic phases created by intermittent flow contain the same lipophilic pH indicator dye but different ion-selective neutral ionophores, different ions can be sequentially and selectively extracted into the different organic phases, where they can be determined by thermal lens microscopy (TLM). We used KD-A3 as the lipophilic pH indicator dye and valinomycin and DD16C5 as neutral ionophores to demonstrate sequential ion sensing of potassium and sodium ions by measuring the deprotonated dye caused by the ion extraction. The integrated microfluidic system proposed here allows multi-ion sensing, which is not easily demonstrated by conventional ion sensor technology using a solvent polymeric membrane. The minimum volume of single organic phase needed to obtain an equilibrium response without dilution by cross dispersion of two organic phases was ca. 500 nL in our system, indicating that the required amounts of expensive reagents in one measurement could be reduced to 1.7 ng and 2.8 ng for the dye and ionophore molecules, respectively.     

Extraction of Tc(VII) with Solutions of Tetraoctylammonium Salts in Toluene and Chloroform

Extraction of pertechnetate anion with solutions of tetraoctylammonium salts (R₄NX, where X^- = Cl^-, Br^-, NO₃ ^-, ClO₄ ^-, ReO₄ ^-) in toluene and chloroform was studied. The TcO₄ ^-/X^- exchange constants in these solvents at a given extracting cation were determined. The linear dependence between the exchange constants of pertechnetate anion and hydration parameters of substituting anions was revealed. The hydration parameter of pertechnetate anions was calculated from this dependence and used to predict the exchange constants of anions in various extraction systems with salts of organic bases.     

Synergistic extraction of rare earth elements from HNO3 solutions with a mixture of CCD and HDBP in a polar diluent

The extraction of Ln(III) (except Pm), La(III), and Y(III) from HNO3 solutions with dibutyl hydrogen phosphate (HDBP), chlorinated cobalt dicarbollide (CCD), and their mixture in a polar diluent, mixture of o-chloronitrobenzene (OCNB) and CCl₄ (1: 1), was studied. A synergistic effect is observed for all the examined elements. For the series La-Dy, it reaches a maximum at the HDBP to CCD molar ratio of 3: 1, and for the series Tb-Lu, at the HDBP to CCD molar ratio of 9: 1. The synergistic effect is observed at the HDBP to CCD molar ratios of up to 700: 1 and 1500: 1 for heavy and light lanthanides, respectively. At higher ratios, the magnitude of the synergistic effect does not exceed the uncertainty of its determination. This fact indicates that one CCD molecule can activate several hundreds of HDBP molecules, enhancing their extraction ability. The degrees of separation of neighboring lanthanides do not noticeably change on introducing CCD into the extraction system. The key component of the hypercomplex is the CCD anion, with the role of the CCD proton being insignificant. A complex of variable composition, containing lanthanide, CCD, and HDBP, is formed in the organic phase.     

Ferric-ion chelation by aminophenol resins

Weak-base, anion-exchange resins of the aminophenol type (Sirorez Fe and Duolite A-7) have been shown to form strongly coloured metal complexes with ferric salts when the sulphate anion is present. The organic structures necessary for the formation of these complexes have been investigated and the capacity of the resins to bind iron over a range of pH and metal ion concentrations determined. The chelation properties of these polymers have been used as a means of selectively removing the ferric ion from mixtures containing a wide range of uni- and multivalent metal ions, including some which normally form strong chelate complexes.     

High-purity nano silica powder from rice husk using a simple chemical method

A highly pure, small particle-sized and high surface area nano silica powder was prepared from rice husk using alkali extraction, followed by an acid precipitation method. The composition, phase, morphology, size and surface area of the as-synthesised nano silica powder was investigated by energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, particle size analyser and BET surface area analyser. High-purity nano silica powder was obtained by sodium hydroxide (NaOH) purification treatment (0.5, 1, 1.5, 2 and 2.5?N). The high purity of silica (～99.9%) was obtained at 2.5?N NaOH treatment. The pure nano silica powder that is obtained shows an average particle size of ～25?nm with a high-specific surface area (SSA) of 274?m²?g^?1, with an average pore diameter of 1.46?nm.