Equilibrium and Transport Characteristics of Perfluorinated Cation-Exchange Membranes Containing Carboxyl Groups

Equilibrium (the exchange capacity and moisture content) and transport (the ion transport numbers and the electrical conductance) properties of perfluorinated cation-exchange membranes containing carboxyl groups were studied as a function of pH and concentration of KCl solutions (10^–4–1 M). Dissociation constants of carboxyl groups, adsorption potentials of K⁺ ions, transport numbers and mobilities of counterions in the membranes, concentrations of fixed ions, co- and counterions, as well as the Donnan potentials were calculated.     

Thermoosmosis of various electrolyte solutions through anion-exchange membranes

Thermoosmosis through anion-exchange membranes was measured for 10^-3 to 2 mol/kg of aqueous KCl, LiCl, and NH₄Cl and for 10^-3 to 3 x 10^-1 mol/kg of aqueous KIO₃ and K₂SO₄. For all electrolytes used the direction of thermoosmosis was from the cold side to the hot side over the whole range of concentrations. For KCl and LiCl the experimental results were analyzed with an extension of a previously published theory, using additional data for transport numbers of ions in membranes and for electroosmosis. The agreement between theory and experiment is satisfactory. The absolute value of thermoosmosis for KIO₃ is larger than that for other electrolytes because the pore volume fraction of the membrane for KIO₃ is larger than that for the other electrolytes.     

Spectrophotometric Analysis of some Phenothiazine Neuroleptics using Chloramine-T

ABSTRACT

A sensitive and selective spectrophotometric method has been developed for the determination of six phenothiazine neuroleptics. The method is based on the interaction of the drugs with chloramine-T in sulphuric acid medium to yield a red, reddish-violet, orange or greenish-blue intermediate with maximum absorption at 500-636 nm. Beer's law is obeyed over the range 5-125 μg ml^?1 of the drugs. The apparent molar absorptivities were found to be in the range 1.04x10³ to 5.46x10³ 1.mol^?1cm^?1. The investigated drugs were assayed in tablets and injections. The mean percentage recoveries were 97.65-101.75 and the relative standard deviations were found to be less than 2%.     

Permeation of aromatic compounds in aqueous solutions through thin,dense cellulose acetate membranes

The partition and diffusion coefficients of aqueous solutions of aromatic compounds through a thin, dense cellulose acetate membrane were measured at 20°C. The water content and the thickness of the prepared membranes varied from 0.121 to 0.610 by volume fraction and from 17 to 88 μm, respectively. The aromatic solutes used were phenol, aniline, hydroquinone and p-chlorophenol. The solute concentration ranged between 9.0 x 10^-5 and 1.0 x 10^-3 mol/l. The partition coefficients had the following order: p-chlorophenol, phenol, aniline, hydroquinone; they were experimentally correlated with the water content of the swollen membranes.The dependence of the diffusion coefficients on the water content of the membrane was examined using as basis a pore model and a free volume model, respectively. The diffusion coefficients were adequately correlated with the water content of the membrane according to the relation given by the free volume model.     

Amperometric sensor for pyruvate with immobilized pyruvate oxidase

Several procedures for immobilization of pyruvate oxidase by chemical bonding are reported. Attachment to nylon net was unsatisfactory in terms of yield and stability. Polyazetidine, a new commercially available prepolymer and a new nylon membrane with surface carboxyl groups provided good long-term stability, up to 30 days in the case of the nylon membrane. Under optimal conditions of solution preparation (0.1 mmol 1^-1 thiamine pyrophosphate, 0.5 mmol 1^-1 phosphate, 2.5 mmol 1^-1 calcium and 0.04 mol 1^-1 Tris buffer pH 7.0), linear calibration graphs were obtained until the lowest concentration of 10^-3 mmol 1^-1 pyruvate and amperometric sensors based on these membranes. With careful standardization, the procedures were suitable for application to blood serum.     

Kinetics and mechanism of the cleavage of n-methoxyphthalimide (NMPT) in the presence of buffers of tris (hydroxymethyl)amino methane (tris) and 1,4-diazabicyclo[2.2.2]octane (DABCO)

The magnitude of hydroxide ion-catalyzed second-order rate constant (k_OH) for hydrolysis of N-methoxyphthalimide (NMPT) supports the conclusion that the rate law for pH-independent hydrolysis of N-hydroxyphthalimide (NHPTH) is rate = k_OH[HO^-][SH] where SH represents nonionized NHPTH. The second-order rate constants for the reactions of NMPT with DABCO and Tris are (59.7 ± 6.9) x 10^-3 and (11.9 ± 2.3) x 10^-4 M^-1 s^-1, respectively. This revised version was published online in June 2006 with corrections to the Cover Date.     

Relationships of Acid and water content to proton transport in statistically sulfonated proton exchange membranes: variation of water content via control of relative humidity

An in-depth analysis for proton exchange membranes to examine the effects of acid concentration and effective proton mobility upon proton conductivity as well as their relationship to water content was carried out on two main-chain, statistically sulfonated polymers at 25 degrees C. These polymer systems consisted of poly(ethylenetetrafluoroethylene-graft-polystyrenesulfonic acid) (1) and sulfonated trifluorostyrene (BAM) membrane (2). Nafion (3) was used for comparison. Water content (as represented by Xv, the water volume fraction, where Xv = volume of water in hydrated PEM / volume of hydrated PEM), for each sample was varied by adjusting the relative humidity (RH) of the membrane environment from 50% to 98%. It was found that, at low RH (RH < 70%), the major factor determining proton conductivity is proton mobility. In order to remove the differences in acid strength for the membranes, proton mobility values at infinite dilution (Xv = 1.0) and 25 degrees C were calculated and found to be 2.6 +/- 0.2 x 10-3 (average of 1a-c), 1.6 +/- 0.3 x 10-3 (average of 2a-e), and 2.32 +/- 0.01 x 10-3 cm2 s-1 V-1 (3). These were then compared to the theoretical value for the mobility of a free proton at infinite dilution and to previously reported data. Possible differences in tortuosity and the juxtaposition of acid groups are proposed in order to account for the significant deviations of all samples from the theoretical value.     

Novel Mixed-Valence μ-Oxo-Bridged Trinuclear Manganese Complexes [Mn3O(O2CR)6L3] (R=4-Cl-C6H4OCH2, 3-Cl-C6H5, BrCH2, L=3-Methylpyridine or Water): Structures and Magnetic Properties

Preparation of three new mixed-valence oxo-centered trinuclear manganese complexes [Mn₃O(O₂CR)₆L₃] (R=4-Cl-C₆H₄OCH₂, 1, 3-Cl-C₆H₅, 2, BrCH₂, 3; L=3-methylpyridine or water), by reaction of N-n-Bu₄MnO₄ with appropriate reagents in ethanol and 3-methelpyridine is reported. The crystal structure of 1 has shown to have an oxo-centered Mn₃O unit with peripheral ligands provided by bridging carboxylate and terminal 3-methylpyridine groups, and with an approximate 3-fold symmetry axis for the whole cluster. Variable temperature magnetic susceptibilities of the complexes in the range 1.5-300 K have been measured and are interpreted in terms of the Kambe vector-coupling method and Van Vleck equation; J (cm^?1), J' (cm^?1), g, and R parameters obtained are -8.2, -10.9, 2.04, 2.15 x 10^?3 (1); -7.3, -11.1, 2.20, 3.32 x 10^?3 (2); -2.1, -4.1, 1.97, 2.34 x 10^?3 (3). There is weak antiferromagnetic exchange between manganese ions. Effects of bridging and terminal ligands on the J, J' values and spin ground state are discussed.     

Retention measurements of nanofiltration membranes with electrolyte solutions

Retention measurements with single salt solutions of CaCl₂, NaCl and Na₂SO₄ revealed that the rejection mechanism of commercial polymeric nanofiltration membranes investigated in this study may be divided into two categories:

• 1.Membranes for which Donnan exclusion seems to play an important role.
• 2.Membranes for which retention is determined by both Donnan exclusion and size effects.

In category 1 both positively and negatively charged membranes were found.Ceramic γ-Al₂O₃ ultrafiltration membranes with a pore size of 3 nm showed a same type of salt retention behavior as the positively charged polymeric membranes.The extended Nernst–Planck equation in combination with the Donnan equilibrium has been used to model the flux-retention experiments for the salt solutions. The numerical calculations resulted in a good agreement with experimental data and acceptable values for the fixed charge densities have been determined. The effective membrane thicknesses calculated were higher than those observed by scanning electron microscopy.     

Applications of electron spin resonance in the analytical chemistry of transition metal ions: Part 3. Determination of Chromium(III) in Aqueous Solution [1]

Chromium(III) can be determined in aqueous solution at pH 1.5– 2.5 by electron spin resonance techniques. The analytical range is 2.0 x 10^-1–2.0 x 10^-6 mol dm^-3 ; the precision is± 0.3%. The effects of instrumental variables are discussed. Few commonly occurring species up to a concentration of 1.0 x 10^-1 mol dm^-3 interfered with the determination. The characteristic g value of 1.98 for chromium(III) suggests that the method may also be used to identify chromium(III).     

Structural and Electrosurface Characteristics of Sulfonated Cation-Exchange Perfluoropolymer Membranes in 1 : 1 Electrolyte Solutions

The equilibrium (the exchange capacity, the structural resistance coefficient, and contact angles) and transport (the conductivity) characteristics of differently obtained sulfonated cation-exchange perfluoropolymeric membranes in 1 : 1 electrolyte solutions were investigated. It was shown that the transformation of membranes from the Na⁺form to the K⁺form sharply decreases their moisture content, which is accompanied by an increase in the structural resistance coefficient and the counterion concentration in membranes. Experimental data were used for calculating the electrochemical characteristics of membranes: efficiency coefficients, ion mobilities and transfer numbers of ions in the intramembrane liquid, as well as Donnan potentials. Measurements of the wettability of fluoroplastic ion-exchange membranes with water and electrolyte solutions showed that the presence of strongly acidic ionogenic groups significantly decreases contact angles as compared with that of the polytetrafluoroethylene surface. It was also established that, for the investigated systems, the contact angle is virtually independent of the composition of the liquid phase.     

Effects of the feed solution concentration on the separation degree in Donnan dialysis for binary systems of amino acids

The separations of amino acids by Donnan dialysis using an ion-exchange membrane were studied. Donnan dialytic experiments were carried out using an anion-exchange membrane, glutamic acid–phenylalanine or glutamic acid–alanine mixed solutions as the feeds, and sodium hydroxide solutions as the stripping ones. The initial concentrations of the two kinds of amino acids in the feed solutions were equal and in the range of 0.5–50 mol m⁻³. The amino acid fluxes were measured for each feed solution. Above the feed concentration of 10 mol m⁻³, the glutamic acid flux was over 100 times greater than that of the other amino acid, and it was found that the Donnan dialysis was applicable to the separation of the amino acids. On the other hand, below 10 mol m⁻³, the amino acid fluxes varied in a complicated manner with the concentration, and below 1 mol m⁻³ there was little difference between the fluxes of the two amino acids.Furthermore, after soaking the membrane in solutions having the same concentrations as the feed in the Donnan dialysis, uptake of the amino acids into the membrane was also measured. By comparing the experimental results of both the flux and uptake of the amino acids, the reason why the flux varied in a complicated manner with the concentration was discussed.     

Sorption and diffusion of organic vapors in poly[bis(trifluoroethoxy) phosphazene] and poly[bis(phenoxy)phosphazene] membranes

The sorption isotherms and diffusivities for vapors of some selected simple alcohols (methanol, ethanol, isopropanol, and 2-butanol), ketones (acetone, methyl ethyl ketone, and methyl isobutyl ketone), and aromatic compounds (benzene, toluene, and xylene) in poly[bis(trifluoroethoxy)phosphazene] (PTFEP) and poly[bis(phenoxy)phosphazene] (PPOP) were determined by integral sorption-desorption experiments at 35°C. The sorption isotherms for these compounds evaluated were almost linear to obey Henry's law for the determination of constant solubility of each solvent vapor species, and the corresponding permeabilities for them can be estimated according to the solution-diffusion model. The diffusivities for these vapors in PPOP (10⁻⁹∼10⁻⁸ cm²/s) were about one order smaller than those in PTFEP (10⁻⁸∼10⁻⁷ cm²/s) because the more rigid phenoxy groups and the higher crystallinity in PPOP may hinder the diffusion of sorbed molecules. Relatively weak dependence of diffusivity or permeability on the vapor activity (or concentration) was found, to be in contrast to the exponential dependence for many organic vapors in rubbery organic polymers, probably due to the limited increase of the free volume in sorption for these vapors in PTFEP and PPOP membranes.     

Determination of copper with neocuproine by thermal-lens spectrometry

Conditions for the spectrophotometric determination of copper with 2,9-dimethyl-l,10-phenan-throline (neocuproine) in the presence of ascorbic acid in a water-ethanol solution (9 : 1) at pH 4.5–5.0 have been found. The detection limit is 3 x 10^-6 M. The concentration range is from 4.4 x 10^-6 to 3 x 10^-4 M. Conditions for the determination of copper(I) with neocuproine by thermal lens spectrometry have been proposed. The detection limit is 4 x 10^-7 M. The concentration range is from 7 x 10^-7 to 6 x 10^-5 M. Iron(II) at concentrations as high asn x 10^-4 M does not interfere with the determination of copper. Changes in the conditions for the photometric reaction associated with passing from spectrophotometric measurements to thermal lensing are discussed.     

Sulfonated polyimides as proton conductor exchange membranes. Physicochemical properties and separation H+/Mz+ by electrodialysis comparison with a perfluorosulfonic membrane

The properties of new sulphonated polyimide membranes (SP) – ion exchange isotherms, electrical conductivity, selectivity and proton–cation electrotransport – are compared with that of perfluorinated Nafion^® membrane. Both membranes when in contact with H⁺/M^z+ aqueous solutions (M^zM+=Na⁺, Cu²⁺, Cr³⁺) present an affinity to cations which increases with their valencies; however the affinity of one of the SP membranes for protons is approximately 10% higher than that of Nafion^®. The proton transport number is also 10% higher for this SP membrane than for Nafion^®. Using SP membranes for electrodialysis of H⁺/Cu²⁺ solutions produces solutions about 10% more concentrated in H⁺ and about 40% less concentrated in Cu²⁺ ions than with Nafion^® membranes in the same conditions. The difference in conductivity may be explained by differences in ionic clustering because of differences in the polymer structure of the two membranes, block copolymer for SP and statistic copolymer for Nafion^®. The difference in properties for the two SP membranes is explained in terms of the chemical structure of the non-sulfonated diamine groups used in the polymer synthesis. These SP membranes seem to be interesting materials for electromembrane processes in acid media.     

Spectrophotometric behaviour of quinolinium oxime-palladium(II) complexes

Summary It has been established that 1-(2-phenyl-2-hydroxyiminoethyl)-1-quinolinium chloride, 1-(2-phenyl-2-hydroxyiminoethyl)-1-isoqui-nolinium chloride, 1-(2-phenyl-2-hydroxyiminoethyl)-1-(4-methyl)-quinolinium chloride and 1-(2-phenyl-2-hydroxyiminoethyl)-1-(6-methyl)quinolinium chloride react with palladium(II) chloride in the pH range 3.3–7.1 and form yellow water-soluble 11 complexes with maximum absorbance at 413 nm. The conditional stability constants of the complexes at the optimum pH of 6.5 are all about 10^4.7, and the molar absorptivities are in the range 2.2–2.6×10³ l·l mole^–1·cm^–1 at pH 6.5 and 413 nm. Beer's law is obeyed up to 3–4×10^–4 M oxime concentration, depending on the oxime determined.     

Construction and evaluation of PVC and sol–gel sensor membranes based on Mn(III)TPP-Cl. Application to valproate determination in pharmaceutical preparations

The construction and general performance of new valproate-selective electrodes based on manganese(III) tetraphenylporphyrin [Mn(III)TPP-Cl], as an ionophore, are presented. The ionophore was incorporated into PVC and ceramic membranes (sol–gel) based on methyltriethoxysilane. The influence of membrane composition and pH and the effect of lipophilic cationic and anionic additives in PVC membranes were investigated concerning their influence on the slope, response time, selectivity and lifetime of the electrodes. The PVC membrane without additive and the sol–gel membrane presented slopes and practical limits of detection of −60.8 mV dec⁻¹ and 5x10⁻⁶ mol l⁻¹ and −60.3 mV dec⁻¹ and 1×10⁻⁴ mol l⁻¹, respectively. The sol–gel membranes displayed higher selectivity for valproate when compared with PVC membranes. These two types of electrodes were coupled to a sequential-injection analysis (SIA) system for the direct determination of valproate in pharmaceutical formulations. The association of Mn(III)TPP-Cl with the sol–gel support inserted in a SIA system provided potentiometric sensors with an analytical range of 1x10⁻³–5x10⁻² mol l⁻¹, with a sample rate of 55 samples per hour and a sample and carrier consumption of 140 and 2,500 μl per determination, respectively.     

Partial molar volumes of tetraalkylammonium hydroxides in aqueous solution at 25°C

The densities of aqueous solutions of tetramethylammonium, tetraethylammonium, tetra-n-propylammonium and tetra-n-butylammonium hydroxide have been measured at 25°C in the concentration range 0.1–1.0 mol-kg^-1 . The apparent and partial molar volumes are calculated from the density measurements. The apparent molar volumes of the solutes show considerable deviation from the Debye-Hülckel limiting law, even at high dilution. The relation for the concentration dependence of the apparent molar volume is given in an analytical form. The limiting apparent molar volumes of the solutes are split into their ionic components by an extrathermodynamic approach and are discussed in terms of ion-solvent interactions. In this way, the limiting partial molar ionic volume for the hydroxide ion is found to be 2 cm³-mol^-1.     

Novel potentiometric and optical silver ion-selective sensors with subnanomolar detection limits

Ten Ag⁺-selective ionophores have been characterized in terms of their potentiometric selectivities and complex formation constants in solvent polymeric membranes. The compounds with π-coordination show much weaker interactions than those with thioether or thiocarbamate groups as the coordinating sites. Long-term studies with the best ionophores show that the lower detection limit of the best Ag⁺ sensors can be maintained in the subnanomolar range for at least 1 month. The best ionophores have also been characterized in fluorescent microspheres. The so far best lower detection limits of 3 × 10⁻¹¹ M (potentiometrically) and 2 × 10⁻¹¹ M Ag⁺ (optically) are found with bridged thiacalixarenes.