A new method for the determination of mobile phase volume in normal and reversed-phase liquid chromatography

Summary A new method for the determination of the mobile phase volume (V _m) in liquid chromatography is presented based on the model regarding the retention of ionic solutes in the presence of eluent electrolytes. TheV _m value can be determined by measuring the retention volumes of two ions that have the same charge in two eluent electrolyte systems. Compared with the methods using isotopically labelled eluent components or inorganic salts asV _m markers, the method presented is proved to give more reasonableV _m values for both normal and reversed-phase liquid chromatography. As well as in binary mixed solvent systems, theV _m values in single solvent systems can be determined by this method.     

Volumetric Properties of Binary Mixtures of the Ionic Liquid 1-Butyl-3-Methylimidazolium Tetrafluoroborate with Aniline

The densities of binary mixtures of an ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF₄], with an aromatic compound, aniline, have been determined over the full range of compositions and over the temperature range 298.15 to 313.15 K at atmospheric pressure using a vibrating-tube densimeter (DMA4500). Excess molar volumes ( V_m^EV_{\mathrm{m}}^{\mathrm{E}} ) have been obtained from these experimental results, and were fitted by the fourth-order Redlich–Kister equation. In addition, partial molar volumes, apparent molar volumes and partial molar volumes at infinite dilution have been calculated for each component. Our results show that values of V_m^EV_{\mathrm{m}}^{\mathrm{E}} decrease slightly when the temperature increases in this system. The results have been interpreted in terms of ion-dipole interactions and structural factors of the ionic liquid and the organic molecular liquid.     

Volumetric properties of 1-iodoperfluorohexane+<Emphasis Type="Italic">n</Emphasis>-octane binary system at several temperatures

New densities are reported over the whole composition range for 1-iodoperfluorohexane+n-octane system at temperatures from 288.15 to 308.15 K at atmospheric pressure. These data have been used to compute the excess molar volumes, V _m ^E. Large positive V _m ^E values have been obtained over the entire range of composition, which increases when the temperature rises. The experimental data were used to calculate the isobaric thermal expansivity, and the quantities (∂V _m ^E/∂T)_p and (∂H _m ^E/∂p)_T. Furthermore, the results have been used to investigate the volumetric prediction ability of the equations of state Soave–Redlich–Kwong, Peng–Robinson, Patel–Teja and Soave–Redlich–Kwong with volume translation.     

Temperature dependence of volumetric behaviour for methyl tert-butylether+1-butanol system

Excess molar volumes and excess isoentropic compressibilities of methyl tert-butylether (MTBE)+1-butanol at 288.15, 293.15, 298.15, 303.15 and 308.15 K and atmospheric pressure have been studied. In order to analyse the temperature dependence of this mixture, isobaric expansibility a, (dV _m ^e dT) _P,xand (dH _m ^e dP ) _T,x, were computed by analytical differentiation of the density and excess molar volume fitting equations. Cubic equation of state (Soave-Redlich-Kwong) has been applied to excess molar volume correlation obtaining binary interaction parameters using different mixing rules. This revised version was published online in July 2006 with corrections to the Cover Date.     

Physico-chemical studies of a biologically active molecule (L-valine) predominant in aqueous alkali halide solutions with the manifestation of solvation consequences

The apparent molar volume (?_V), viscosity B-coefficient and molar refraction (R_M) have been determined of L-valine in aqueous solution of LiCl, NaCl and KCl at 298 K, 303 K and 308 K from density (ρ), viscosity (η) and refractive index (n_D) measurements, respectively. The limiting apparent molar volumes (?_V⁰) and experimental slopes (S_V*) derived from the Masson equation have been interpreted in terms of solute–solvent and solute–solute interactions, respectively. The viscosity data were analysed using the Jones–Dole equation and the derived parameter B has also been interpreted in terms of solute–solvent interactions in the solutions. Molar refraction (R_M) has been calculated using the Lorentz–Lorenz equation.     

Densities and Apparent Molar Volumes of Aqueous H<Subscript><Emphasis Type="Bold">3</Emphasis></Subscript>BO<Subscript><Emphasis Type="Bold">3</Emphasis></Subscript> Solutions at Temperatures from 296 to 573 K and at Pressures up to 48 MPa

Densities of four aqueous H₃BO₃ solutions (0.062, 0.155, 0.315, and 0.529 mol-kg^–1) have been measured in the liquid phase with a constant volume piezometer immersed in a precisely controlled liquid thermostat. Measurements were made at temperatures between 296 and 573 K and pressures from 0.82 to 48 MPa. The total uncertainties of the density, pressure, temperature, and molality measurements were estimated to be less than 0.06%, 0.05%, 10 mK, and 0.0005 mol-kg^–1, respectively. The accuracy of the method was confirmed by PVT measurements on pure water for two isobars (30 and 39 MPa) at temperatures from 313 to 573 K. The experimental and calculated (IAPWS formulation) densities for pure water show excellent agreement which is within their experimental uncertainties (average absolute deviation, AAD=0.012%;). Apparent and partial molar volumes were derived using the measured densities for solutions and pure water, and these results were extrapolated to zero concentration to yield the partial molar volumes of the electrolyte (H₃BO₃) at infinite dilution. The temperature, pressure, and concentration dependencies of the apparent and partial molar volumes were studied. Small pressure and concentration effects on the apparent molar volumes were found at temperatures up to 500 K. The parameters of a polynomial type of equation of state for the specific volume V_sol(P, T, m) as a function of pressure, temperature, and molality were obtained with a least-squares method using the experimental data. The root-mean-square deviation between measured and calculated values from this polynomial equation of state is ±0.2 kg-m^–3 for density. Measured values of the solution densities and the apparent and partial molar volumes are compared with data reported in the literature.     

Absorption and emission properties of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (M = Al,Ga, In) and correlations with molecular electrostatic potential

Substituent effect for a series of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (Mq3) of aluminum, gallium, and indium are investigated using density functional theory (DFT) for the ground state properties and the time-dependent version of DFT (TDDFT) for their absorption and emission properties. A comparison between the ground state energy of mer and fac isomers of all the complexes revealed that the mer configuration is always more stable than fac. The substituent effect is significantly reflected at the fluorescence maximum (λ_F) values whereas the effect is moderate at the absorption maximum (λ_abs) values. The molecular electrostatic potential (MESP) at the metal center (V_M) and the most electron rich region indicated by MESP minimum (V_min), located at the oxygen of phenoxide ring exhibit excellent correlations with the λ_F and Stokes shift (λ_F−λ_abs) values. The study suggests the use of Stokes shift as an experimental quantity to measure the excited state substituent effect while the V_min or V_M emerge as theoretical quantities to measure the same.     

Acoustical study on ternary mixture of dimethyl acetamide (DMAC) in diethyl ether and isobutyl methyl ketone at different frequencies

The experimental density (ρ) and the velocity (U) for ternary mixture of dimethyl acetamide diethyl ether and isobutyl methyl ketone at different frequencies (2, 4, 6 and 8 MH_Z) have been measured at a constant temperature of 308 K. These data have been used to compute acoustic impedance (Z), adiabatic compressibility (K _s), intermolecular free length (L_f ), molar volume (V_m ), molar sound velocity (R), molar compressibility (B), available volume (V _a), Lennard-Jones potential repulsive term exponent (n), relative association (R _A), interaction parameter (X) and excess values of some of the above parameters for entire range of mole fraction and are interpreted to explain molecular interaction occurring in the liquid mixture.     

Thermodynamic Behavior of Non-Ionic Tri-block Copolymers in Water at Three Temperatures

Apparent molar volumes (V _Φ) of aqueous solutions of some copolymers, based on ethylene oxide (EO) and propylene oxide (PO) units, were determined as functions of concentration at three temperatures. Viscosity measurements were also carried out on some of these systems. The effects studied include how the molecular architecture and the molecular weight affect the aggregation of the copolymer, keeping constant the EO/PO ratio. Modeling of the volumetric data yielded the partial molar volume of the copolymer in the standard (V°) and the aggregated (V _M) states, as well as the equilibrium constant for micellization and the aggregation number. Analysis of the viscosity data supported the insights obtained by modeling of the volumetric data. At a given temperature, both V° and V _M, normalized for the number of the EO and the PO units, are linearly related to the fraction of the EO in the copolymer, regardless of the copolymer nature. These correlations are powerful tools for predicting values of both V° and V _M for copolymers not yet investigated. For macromolecules having the same molecular architecture, the standard Gibbs free energies of micellization () are slightly negative within the errors of their determination, and are hardly affected by temperature changes. Also, their aggregation numbers are small. From the quantitative analysis of the viscosity data, insights were obtained that corroborated the thermodynamic findings. Finally, values of , normalized for the EO and the PO units, show that the same driving forces control the self-assembling processes for copolymers having different molecular weight but the same EO/PO ratio.     

Excess Molar Volumes and Excess Logarithm Viscosities for Binary Mixtures of the Ionic Liquid 1-Butyl-3-methylimidazolium Hexaflurophosphate with Some Organic Compounds

Experimental data of densities and viscosities are presented for the mixtures of the ionic liquid 1-butyl-3-methylimidazolium hexaflurophosphate, [C₄mim][PF₆], with acetone, 2-butanone, 3-pentanone, cyclopentanone and ethyl acetate at 298.15 K. Based on these data, excess molar volumes, V_m^E, and excess logarithm viscosities, (lnη)^E, have been determined for the binaries. It is shown that all values of V_m^E are negative but those of (lnη)^E are positive. Interestingly, a minimum in V_m^E and a maximum in (lnη)^E are observed at about the same mole fraction of the ionic liquid (x = 0.3) for every mixture investigated. Combined with the V_m^E data reported in literature, the effects of the [PF₆]⁻ and [BF₄]⁻ anions are compared. The results have been discussed in terms of the ion–dipole interactions of the cations of the ionic liquids with the organic compounds as well as their influence on the association of [C₄mim]⁺ and [PF₆]⁻ in the ionic liquid.     

Liquid Solution Densities of Ternary-Pseudobinary Mixtures of (Benzene + Cyclohexane) in the Presence of Tetrachloromethane or <Emphasis Type="Italic">n</Emphasis>-Hexane

Densities have been obtained as a function of composition for ternary-pseudobinary mixtures of [(benzene + tetrachloromethane or n-hexane) + (cyclohexane + tetrachloromethane or n-hexane)] at atmospheric pressure and the temperature 298.15 K, by means of a vibrating-tube densimeter. Excess molar volumes, V_m^E, partial molar volumes and excess partial molar volumes were calculated from the density data. The values of V_m^E have been correlated using the Redlich–Kister equation and the coefficients and standard errors were estimated. The experimental and calculated quantities are used to discuss the mixing behavior of the components. The results show that the third component, CCl₄ or n-C₆H₁₄, have quite different influences on the volumetric properties of binary liquid mixtures of benzene with cyclohexane.     

Molecular interaction studies in ternary liquid mixture of dimethylacetamide using ultrasonic technique at 308 K

The experimental density (ρ) and ultrasonic velocity (U) for ternary mixture containing dimethylacetamide (DMAC), acetone and diethyl ether at frequencies 2, 4, 6 and 8 MHz have been measured at temperature 308 K. These data are used to compute adiabatic compressibility (K_s), intermolecular free length (L_f), acoustic Impedance (Z), molar volume (V_m), molar sound velocity (R), molar compressibility (B), available volume (V_a), Lennard-Jones potential repulsive term exponent (n), relative association (R_A), interaction parameter (χ) and some excess thermo acoustic parameters for whole range of concentration of DMAC and are interpreted to elucidate molecular interaction occurring in the liquid mixture.     

Effect of Temperature on the Volumetric Properties of [Difurylmethane+(C<Subscript>2</Subscript>–C<Subscript>6</Subscript>) Alkan-1-ol] Binary Systems: Analyses of New and Literature Density Data in the Temperature Range 288.15–308.15 K

Densities, ρ, of the binary systems {difurylmethane + (ethanol or propan-1-ol or butan-1-ol or pentan-1-ol or hexan-1-ol)} have been measured with an Anton Paar DMA 4500 vibrating-tube densimeter over the entire composition range at 288.15 and 308.15 K and atmospheric pressure. The measured and literature densities of [difurylmethane + n-alkanol] binary systems have been used to check the validity of the relationship describing the dependence of density on composition. This relation is useful for obtaining interpolated ρ values corresponding to the experimental data. Excess molar volumes (V _m^E) of each mixture, limiting (V _m,i ^E,∞) and excess partial (V _m,i ^E) molar volumes and the limiting partial molar expansion (E _p,i ^∞) of both components of each binary system have been examined to provide insight into the temperature variations of the intermolecular interactions and molecular packing efficiencies. The results have been discussed in terms of specific intermolecular interactions and structural effects.     

The initial stage of salt passivation of metals

A theoretical model of the nucleation of a passivating salt layer on the surface S of an anode-dissolving metal was developed. The layer is considered a new phase formed by the mechanism of heterogeneous nucleation, which serves as a related substrate for subsequent growth of the passivating layer. According to experiments, the surface S of real metals is inhomogeneous, that is, anode current density fluctuates on S. It is assumed that, at large current fluctuations, localized regions with volume ΔV _ϕ appear, in which the C _M and C _A concentrations of the M ^z+ and A ⁿ⁻ ions are increased. At fairly large current fluctuations, these concentrations can reach saturation. For this reason, the ΔV _ϕ regions are treated as mother phases, in which A _a M _m salt nuclei are formed with a certain probability. The formation of such ΔV _ϕ volumes and the kinetics of formation of nuclei in them, from which a passivating layer with a finite thickness is formed, are considered.     

Volume dependence of thermal conductivity and bulk modulus for poly(propylene glycol)

The thermal conductivity λ and heat capacity per unit volume of poly(propylene glycol) PPG (0.4 and 4.0 kg·mol⁻¹ in number-average molecular weight) have been measured in the temperature range 150–295 K at pressures up to 2 GPa using the transient hot-wire method. At 295 K and atmospheric pressure, λ = 0.147 W m⁻¹K⁻¹ for PPG (0.4 kg·mol⁻¹) and λ = 0.151 W m⁻¹K⁻¹ for PPG (4.0 kg·mol⁻¹). The temperature dependence of λ is less than 4 × 10⁻⁴ W m⁻¹K⁻² for both molecular weights. The bulk modulus has been measured in the temperature range 215–295 K up to 1.1 GPa. At atmospheric pressure, the room temperature bulk moduli are 1.97 GPa for PPG (0.4 kg·mol⁻¹) and 1.75 GPa for PPG (4.0 kg·mol⁻¹). These data were used to calculate the volume dependence of $ \lambda ,g\, = - \left( {\frac{{\partial \lambda /\lambda }}{{\partial V/V}}} \right)_T $. At room temperature and atmospheric pressure (liquid phase) we find g = 2.79 for PPG (0.4 kg·mol⁻¹) and g = 2.15 for PPG (4.0 kg·mol⁻¹). The volume dependence of g, (∂g/∂ log V)_T varies between −19 to −10 for both molecular weights. Under isochoric conditions, g is nearly independent of temperature. The difference in g between the glassy state and liquid phase is small and just outside the inaccuracy of g of about 8%. The theoretical model for λ by Horrocks and McLaughlin yields an overestimate of g by up to 120%. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 345–355, 1998     

Zur Chemie und Strukturchemie der Phosphide und Polyphosphide. 29. Die molaren Volumina von Metall-Phosphiden,ein Beitrag zur Raumchemie der festen Stoffe

Chemistry and Structural Chemistry of Phosphides and Polyphosphides. 29. Molar Volumes of Metal-Phosphides, a Contribution to the “Raumchemie” of Solids After a short introduction into the “Raumchemie” of solids, developed in 1934 by W. Biltz, the behaviour of the molecular volumes of phosphorus in metal phosphides is discussed. In the case of salt-like phosphides the volume increment of phosphorus, V_P, which is obtained after removal of the cation increment, increases with increasing negative charge z_P of the phosphide ions P^z (?0.07 ≥ z ≥ ?3) and on the other hand decreases with increasing cation charge z_M. The relations are shown by the interpolation equation V_P(z_P, z_M) = exp (αz_Pz_M + βz_P + γz_M + δ) with α = 0.046, β = ?0.368, γ = ?0.066, δ = 2.630. There is no observable difference between compounds with A and B metals. Special conditions due to crystal structure and chemical bonding are discussed. Semimetallic phosphides are appropriately discussed on the basis of the volumes of the metals and of increments of semimetallic phosphorus. Here the V_P values lie between 10 and 6 cm³ · mol^?1. They become smaller as the ratio M/P increases. Some examples are given to show that in special cases the volume can be used to judge the type of bonding. The statement of tho theorem of optima1 volumes is explained for a group of salt-like phosphides. Our study shows, that the “Raumchemie” of BILTZ reliable on the field of metal phosphides.