Ternary diffusion coefficients of diethanolamine and N-methyldiethanolamine in aqueous solutions containing diethanolamine and N-methyldiethanolamine

Ternary diffusion coefficients of diethanolamine (DEA) and N-methyldiethanolamine (MDEA) in aqueous solutions containing DEA and MDEA using the Taylor dispersion technique have been measured for temperatures (303.2, 313.2, and 323.2 K). The systems studied were aqueous solutions containing total amine concentrations of 2.5 and 4.0 kmol m⁻³, each having four different amine molar ratios. The density and viscosity of the blended amine solutions were also measured. The mutual diffusion coefficients of aqueous DEA and aqueous MDEA solutions were also reported. The main diffusion coefficients (D₁₁ and D₂₂) and the cross-diffusion coefficients (D₁₂ and D₂₁) were reported as function of temperature and concentration of alkanolamines. The limiting conditions for the main diffusion coefficients and the cross-diffusion coefficients were discussed at first, and a comparison between the ratios of the cross-diffusion coefficients to the main diffusion coefficients for DEA and MDEA was made. The dependence of the main diffusion coefficients on the viscosity of solutions was also investigated.     

Ternary diffusion coefficients of diethylene glycol and lithium chloride in aqueous solutions containing diethylene glycol and lithium chloride

In this work, ternary diffusion coefficients of diethylene glycol and lithium chloride in aqueous solutions containing diethylene glycol and lithium chloride were reported for temperatures (303.2, 308.2, and 313.2 K) using the Taylor dispersion method. The investigated ternaries contained total glycol–salt concentrations of 10, 15, and 20 wt%. The main diffusion coefficients (D₁₁ and D₂₂) and the cross-diffusion coefficients (D₁₂ and D₂₁) were discussed as function of temperature and concentration. A modified equation originally proposed by Batchelor [1] for mixture of hard spheres in a continuum solvent was used to correlate the present diffusion coefficient data and the results are satisfactory.     

Enthalpic interactions of -alanine and -serine in aqueous urea solutions

The enthalpies of dilution of -alanine and -serine in various aqueous urea solutions have been determined by flow microcalorimetry at 298.15 K. The homogeneous enthalpic interaction coefficients over the whole range of aqueous urea solutions have been calculated according to the excess enthalpy concept. The results were interpreted from the point of view of solute–solute interactions moderated by solvent effects.     

Measurements of binary diffusion coefficients for metal complexes in organic solvents by the Taylor dispersion method

Infinite dilution binary diffusion coefficients, D₁₂, of ferrocene, 1,1′-dimethylferrocene and ethylferrocene in hexane, cyclohexane and ethanol at 313.2 K and pressures from 0.2 to 19 MPa, in acetonitrile at 298.2–333.2 K and 0.2 MPa, and various metallic acetylacetonate, acac, complexes such as Co(acac)₃, Ru(acac)₃, Rh(acac)₃, Pd(acac)₂ and Pt(acac)₂ mainly in ethanol at 313.2 K and 0.2 MPa were measured by the Taylor dispersion method. The D₁₂ values in m² s⁻¹ for the three ferrocenes in the present study and those of ferrocene and 1,1′-dimethylferrocene in supercritical carbon dioxide in our previous studies were represented by the modified hydrodynamic equation over a wide range of viscosity: M^0.5D₁₂/T = 1.435 × 10⁻¹³η^−0.8446 with average absolute relative deviation of 2.40% for 316 data points, where M is the solute molecular weight, T is the temperature in K, η is the solvent viscosity in Pa s. Although the D₁₂ values for the acac complexes were roughly represented by the above hydrodynamic equation, the accuracies were lower because they were dependent on not solute molecular weight but the number of acac ligand in the complex molecules.     

Binary mutual diffusion coefficients of aqueous ammonium and potassium sulfates at 25°C

The diffusion coefficients of aqueous ammonium and potassium ions at infinite dilution differ by only 0.01% at 25°C, so, according to Nernst's law, the binary mutual diffusion coefficients D of pairs of dilute aqueous ammonium and potassium salts should be nearly identical. Yet precise optical interferometric data for ammonium and potassium sulfates contradict this rule: the value of D reported previously for 0.05 mol-L⁻¹ aqueous ammonium sulfate is 0.80×10⁻⁵ cm²-s⁻¹, while the corresponding value for potassium sulfate is 1.24×10⁻⁵ cm²-s⁻¹ about 50% higher. To confirm this surprising result, the diffusion coefficients of the two salts have been measured by the Taylor dispersion technique. The diffusion coefficients of the salts are indeed nearly identical, and the earlier ammonium sulfate data are found to be incorrect.     

Taylor dispersion measurements at low electrolyte concentrations. I. Tetraalkylammonium perchlorate aqueous solutions

An equipment for the determination of mutual diffusion coefficients using the Taylor's dispersion technique is described. The radius of the capillary was determined with the help of various calibration methods. Diffusion coefficients of aqueous tetraalkylammonium perchlorates, Me₄NClO₄, and Et₄NClO₄, were measured at 25°C in the concentration range 10^–3 to 5×10^–2 mol-dm^–3, and the slightly soluble Pr₄NClO₄ up to 1×10^–2 mol-dm^–3. The slope of linear plots ofD vs. is in agreement with theory, in contrast to the limiting valuesD ₀, which all deviate by about –5% from the Nernst-Hartley values.     

Activity coefficients and diffusion coefficients of dilute aqueous solutions of lithium,sodium, and potassium hydroxides

A simplified version of Harned's conductimetric technique has been used to measure binary diffusion coefficients of aqueous lithium, sodium, and potassium hydroxides at 25°C from 0.002 to 0.14 mol-dm^–3. Because of the large difference in mobility between OH^– and the cations, the electrophoretic effect tends to reduce the rate of diffusion of the alkali metal hydroxides; the largest effect is observed for LiOH solutions. The measured diffusion coefficients are in excellent agreement with predictions of the Onsager-Fuoss theory of ion transport. Precise activity coefficients determined from the diffusion measurements are compared with activity coefficients obtained previously by emf methods.     

Ternary mutual diffusion coefficients of KCl-LaCl3-water mixtures from taylor dispersion profiles

The Taylor dispersion (peak-broadening) method is used to measure ternary mutual diffusion coefficients at 25°C for fifteen different compositions of the system KCl–LaCl ₃ -water at ionic strengths from 0.02 to 0.24 mol-dm^–3. The diffusion coefficients are evaluated by least-squares analysis of the refractive index profiles across the dispersed solute peaks. Diffusing LaCl ₃ is found to cotransport significant amounts of KCl. Monte Carlo simulations are used to estimate the precision of ternary diffusion coefficients determined by the dispersion method. Tracer diffusion coefficients are also reported for La ³⁺ ions in aqueous KCl solutions and for K⁺ ions in aqueous LaCl ₃ solutions.     

Interactions of DL-serine and L-serine with NaCl and KCl in aqueous solutions

The activity coefficients at 25‡C of DL-serine and L-serine in aqueous solutions of NaCl and KC1 were measured. This study examines the effect of the nature of the cation of the electrolyte on the activity coefficients of the optical-isomers of serine in aqueous solutions for molality of serine up to 0.4 and molality of electrolyte up to 1. An electrochemical cell with two ion-selective electrodes, a cation, and an anion ion selective electrode,vs. a double-junction reference electrode was used to measure the activity coefficients of the electrolyte and the results were converted to the activity coefficients of serine in the aqueous electrolyte solution. The comparison of the results obtained for DL- and L-serine indicates that the two optical isomers have identical interactions with electrolytes in aqueous solutions and that for this amino acid the effect of the cation of the electrolyte is not significant. Comparison of these results with previous measurements for DL-alanine in aqueous solutions of the same electrolytes show the notable effect of the backbone of the amino acid.     

Dynamic surface tension,critical micelle concentration,and activity coefficients of aqueous solutions of nonyl phenol ethoxylates

Dynamic surface tensions, σ(t) for aqueous solutions of nonyl phenol ethoxylates (NPEOs) at the temperature 298.15 K were measured using a Lauda drop volume tensiometer. The non-ionic surfactants analyzed in this work were Tergitol NP-9, NP-35 and NP-40. By using the classical Ward and Torday equation, the diffusion coefficient for each bulk surfactant concentration was calculated. The equilibrium surface tension values were determined by extrapolating the dynamic surface tension to t → ∞ on the σ(t) vs. t^−1/2 curves. These values were used to determine the critical micelle concentrations (CMC) of the surfactant aqueous solutions as well as to calculate the infinite dilution activity coefficient of the surfactant, following a model that combines the Volmer surface equation of state and the Gibbs adsorption equation.     

Transport properties of alkyltrimethylammonium bromide surfactants in aqueous solutions

Differential mutual diffusion coefficients of n-alkyltrimethylammonium bromides [CH₃(CH₂)_n–1N(CH₃)₃Br, C_nTAB] (n=10, 12, 14, 16) have been measured in aqueous solutions at 298.15 K using a conductimetric cell and an automatic apparatus to follow diffusion. The cell is based on an open-ended capillary, and the technique follows the diffusion process by measuring the resistance of a solution inside the capillaries at various times. The electrical conductances of those solutions have also been measured to calculate the critical micellar concentration (cmc). Thermodynamic analysis of the data suggests that the free ion concentration decreases at concentrations above the cmc, in agreement with theoretical predictions. The obtained values of the micellization parameters were used to model the mutual diffusion coefficients of C_nTAB aqueous solutions.     

Acid-base chemistry of omeprazole in aqueous solutions

Omeprazole is a potent anti-acid drug. Its absorption and mode of action are closely related to its prototropic behavior. In the present study, omeprazole samples from different sources and in different forms were studied spectrophotometrically to obtain pK_a values. In the neutral to alkaline pH region, two consistent pK_a values of 7.1 and 14.7 were obtained from various samples. The assignment of these pK_a values was realized by comparison with the prototropic properties of N(1)-methylated omeprazole substituted on the nitrogen at the 1-position of the benzimidazole ring, which was found to have a pK_a of 7.5. The omeprazole pK_a of 14.7 is assigned to the dissociation of the hydrogen from the 1-position of the benzimidazole ring and the pK_a of 7.1 is assigned to the dissociation from the protonated pyridine nitrogen of omeprazole. The results presented are at variance with those of earlier work.     

Diffusion coefficients of the ternary system (2-hydroxypropyl-β-cyclodextrin + caffeine + water) at T = 298.15 K

Ternary mutual diffusion coefficients measured by Taylor dispersion method (D₁₁, D₂₂, D₁₂, and D₂₁) are reported for aqueous solutions of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) + caffeine at T = 298.15 K at carrier concentrations from (0.000 to 0.010) mol · dm⁻³, for each solute, respectively. These diffusion coefficients have been measured having in mind a better understanding of the structure of these systems and thermodynamic behaviour of caffeine and 2-hydroxypropyl-β-cyclodextrin in solution. For example, from these data it will be possible to estimate some parameters, such as the fraction of associated species HP-β-CD (X₁) and caffeine (X₂) in this complex, the monomer and dimer fractions, and , respectively, and the limiting diffusion coefficients of the HP-β-CD, , of the dimers caffeine entities, , and of those complexes (1:1), .     

Binary diffusion coefficients of phenolic compounds in subcritical water using a chromatographic peak broadening technique

Infinite dilution diffusion coefficients of certain phenolic compounds were measured as a function of temperature in water slightly acidified with formic acid using the Taylor dispersion method. The diffusion coefficients calculated using the chromatographic peak broadening technique were found to increase exponentially with an increase in the temperature. The diffusion coefficients of the selected phenolic compounds did not vary as a function of their molecular weights and the diffusion coefficients of the phenolic compounds increased as a function of temperature (from 2.16 × 10⁻¹⁰ m² s⁻¹ at 298 K to 5.79 × 10⁻¹⁰ m² s⁻¹ at 413 K for malvidin-3,5-diglucoside). However, for some phenolic compounds such as gallic acid monohydrate, quercetin-3-β-d-glucoside, protocatechuic acid and (−)-epicatechin, there were difficulties in making measurements above temperatures of 352 K, 372 K, 392 K and 413 K, respectively, due to thermal degradation of the phenolic compounds in water above these temperatures. The experimentally measured diffusion coefficients of the phenolic compounds were correlated as a function of temperature and solvent viscosity and were compared with those predicted using theoretical models. The validity of the Stokes-Einstein diffusion model in predicting the diffusion coefficients of the phenolic compounds in hot pressurized water was also evaluated.     

Correlation between apparent molal volume and osmotic coefficient in aqueous nonelectrolyte solutions

A linear correlation between apparent molal volume and osmotic coefficient in aqueous solution is derived for the multiple association process of solute molecules (purine-like compounds). The same correlation has been empirically fitted also by other solutes (urea and urea derivatives) for which aggregation is a matter of debate or may be ruled out. The relation is briefly discussed in terms of the current view on the physicochemical properties of the solvent water.     

Comparison of methods for the determination of diffusion coefficients of polymers in dilute solutions: The influence of polydispersity

A comparison between various methods to determine diffusion coefficients of polymers in dilute solutions has been made. It is shown that Taylor dispersion analysis (TDA), dynamic light scattering (DLS), hydrodynamic chromatography (HDC), and size exclusion chromatography (SEC) can all be used to accurately determine diffusion coefficients when the polymer samples have low polydispersities. By the analysis of a series of practically representative styrene acrylonitrile copolymer (SAN) samples, it is shown that polydispersity of the samples and the presence of low‐molecular‐mass material cause considerable differences between the methods. It was found that TDA is mostly disturbed by the presence of low‐molecular‐mass material, whereas DLS is more sensitive to the polydispersity of the polymer. With broad samples, DLS gives the Z‐average diffusion coefficient. SEC can be used to obtain a diffusion coefficient distribution as well as an average diffusion coefficient of a polydisperse sample. Although, the same was expected for HDC, it was found that this method could only be successfully used for polymer samples having low polydispersities. Deviations between SEC, HDC, and TDA found for narrow samples were not related to the chemical composition of the samples. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 593–603, 1999     

Determination of diffusion coefficients of Cu(I) ions in concentrated perchlorate solutions

The diffusion coefficients of Cu(I) ions in concentrated aqueous Ca(ClO₄)₂ solutions have been determined from the limiting currents of anodic oxidation at the rotating disc electrode.

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Zur Bestimmung der Diffusionskoeffizienten von Cu(I)-Ionen in konzentrierten Perchloratlösungen (Kurze Mitteilung)

Zusammenfassung Diffusionskoeffizienten von Cu(I)-Ionen in konzentrierten wäßrigen Ca(ClO₄)₂-Lösungen wurden durch Messung der anodischen Grenzströme an der rotierenden Scheibenelektrode bestimmt.

     

Ternary mutual diffusion coefficients of aqueous {l-dopa (1) + β-CD (2)} solutions at T = 298.15 K

Ternary mutual diffusion coefficients (D₁₁, D₂₂, D₁₂ and D₂₁) measured by the Taylor dispersion method are reported for aqueous solutions of {levodopa (l-dopa) + β-cyclodextrin (β-CD)} solutions at T = 298.15 K and concentrations up to 0.007 mol · dm⁻³. Significant effects on the diffusion were observed, suggesting interactions between this carbohydrate and l-dopa. Support for this came from ¹H NMR spectroscopy, which shows that these effects are due to formation of 1:1 (β-CD:l-dopa) complexes.     

Counterion-accelerated diffusion of aqueous serum albumin

A modified Harned conductimetric procedure has been used to measure binary diffusion coefficients at 25°C for aqueous sodium and potassium salts of the protein bovine serum albumin (M _n BSA; M=Na⁺ or K⁺; n=2 to 23). The condition of electroneutrality requires that the BSA ions diffuse at the same speed as the relatively mobile sodium or potassium counterions. Consequently, the protein ions diffuse 3 to 8 times more rapidly than the isoionic protein diffuses. An approximate analysis of counterion-accelerated diffusion of high molecular weight solutes is presented which shows that the increase in diffusivity with the number of counterions is a thermodynamic effect brought about by an increase in the free energy gradient of the solutes.     

Coupled tracer diffusion coefficients of solubilizates in ionic micelle solutions from liquid chromatography

The peak-broadening (Taylor dispersion) method is used to measure the diffusion of traces of alcohols (ethanol, n-butanol, n-hexanol, n-octanol, n-decanol) in aqueous solutions of sodium dodecylsulfate micelles at 25°C. A small quantity of each alcohol is injected into a long capillary tube containing a laminar stream of the micelle solution. The tracer diffusion coefficient is calculated from the broadened distribution of the eluted alcohol which is measured by differential refractometry. The fraction of each alcohol that is solubilized by the micelles is estimated from the drop in the diffusion coefficient relative to the value for the free alcohol molecules in pure water. The refractive index profiles across the dispersed samples are analyzed to obtain the cross-diffusion coefficient which gives the coupled flow of sodium dodecylsulfate produced by the tracer diffusion of each alcohol.