A comparative study of the volumetric properties of dilute aqueous solutions of 1-propanol, 1,2-propanediol, 1,3-propanediol, and 1,2,3-propanetriol at various temperatures

Excess molar volumes and partial molar volumes were determined for dilute aqueous solutions of 1-propanol, 1,2-propanediol, 1,3-propanediol, and 1,2,3-propanetriol, at temperatures of (283.15, 288.15, 293.15, 298.15, 303.15, and 308.15) K from density measurements. The infinite dilution partial molar volumes of alcohols in aqueous solution were obtained by extrapolation at each temperature. The volumetric behavior of aqueous alcohol and polyol solutions is discussed in terms of the relationship between polar and non-polar groups and its effect on water structure.     

Partial molar volumes of amino acid derivatives in water

The partial molar volumes at infinite dilution for a number of hydrochlorides and sodium salts of N-methyl derivatives of , -aminocarboxylic acids in water at 25°C are measured and related to their van der Waals volumes. Results indicate that 4.96±0.48 water molecules hydrate a betaine hydrochloride. Volumes of proton ionization and interaction terms are evaluated. Group contributions to the partial molar volumes are also reported.     

Effect of temperature on ionic volumes and heat capacities in methanol

A flow densimeter and flow heat capacity calorimeter have been employed to measure precision densities and specific heats of selected electrolytes and nonelectrolytes in methanol at 20, 25, and 40°C. Apparent molar volumes and heat capacities have been calculated and the corresponding standard state functions, V ^o and C _p, ^o , evaluated. The data have been used, along with known volumes and heat capacity data at 25°C for numerous alkanes, to generate volumes and heat capacities of model compounds for organic electrolytes. Comparison of the thermodynamic functions for the model compounds with those of the corresponding electrolytes at the respective temperatures has made it possible to assign single ion values and to establish the temperature effects of ionic charges on the volumes and heat capacities of solutes.     

Aqueous Capillary Electrophoresis of Peptides Part 1: Conformational States, Volumes and Estimates of the Extent of Hydration

Summary A series of eighteen peptides have been modelled. Of the 380 low-energy viable conformers generated, 64 were selected, with 2–5 per peptide representing the range of structures and size. Using the results of previous investigations of this peptide group, it was possible to place an upper limit to the extent of hydration for each peptide. The modelled peptides were then hydrated in stepwise fashion. From the volumetric and dimensional data derived, in conjunction with published mobilities, the relationship between electrophoretic mobility ( _ep ) and the hydrodynamic radius (r) was used to objectively test the fit between the experimental ( _ep ) data and and the modelled size parameters over the range of hydration. Where the fit was tightest it was presumed that the fraction of the maximum reasonable hydration best represented the average degree of hydration of the set. Using ellipsoidal volumes, Connolly surfaces and excluded volumes the average degree of hydration was found to be in the mid range considered and corresponded to the mean of the bimodal distribution of hydration for the individual peptides according to charge-based calculations. For a peptide with two positive charges and a partial negative charge on the carboxy residue (pH=2.5), about 15 waters of hydration are indicated. With 3, 5 and 6 positive charges, the estimated waters are 28, 48 and 85, respectively. Van der Waals volumes were not helpful as the precise summation of the volumes associated with each bonded atom is a poor reflection of the effective volume of the migrating peptide. Conformational changes are examined as a function of the progressive hydration, and, as might be expected, the greatest changes occur in the early stages of hydration.     

Liquid chromatography of phenolic compounds in natural water using on-line trace enrichment

Summary Two packing materials, C18 and PLRP-S, are studied for on-line trace enrichment of phenolic compounds in water. Various precolumns of different internal diameter are also tested and the addition of an ion-pair reagent to increase retention and thus, breakthrough volumes of phenolic compounds, is studied. Best results are obtained when a PLRP-S precolumn is coupled on-line with a C18 analytical column and DAD detector. Addition of TBA considerably increases breakthrough volumes. In contrast, when a C18 precolumn is used, breakthrough volumes are lower and it is impossible to determine TCP and PCP, under the experimental conditions used, because of interference of other nonpolar compounds in the samples. The performance of the system is evaluated with river and tap water and the preconcentration of 10 ml of sample in a PLRP-S precolumn involves a linear range between 1 g 1^–1 and 20 l^–1 and limits of determination between 0.5 g l^–1 and 1 g l^–1 are obtained.     

Zone formation in ion-pair RPLC II. System peak retention and effects of desorption of organic ions on established column equilibria

Summary Desorption of some organic ions from Bondapak Phenyl was studied. The half height of the desorption curve was used to describe the retention volumes. When the column was equilibrated with two organic ions with opposite charge and one of them was desorbed, the other ion was also partially desorbed and observed as a positive zone. The retention volumes of systems peaks created by disturbing the equilibria in the column, equilibrated with at least one organic ion, were studied. The net retention volumes of the break-through curve, obtained from the adsorption of organic ions, system peaks and desorption curves were compared. At low concentrations of the adsorbable ion in the eluent all three types of retention volumes were equal. Negative zones, obtained when introducing an organic ion into a column equilibrated with an organic ion of the opposite charge, could be used to perform step gradient elution of ionic compounds. By using suitable conditions narrow peaks were obtained.     

The development of analytical methods for the determination of ions and acidity in individual raindrops

Summary In this publication the first results of a microanalytical investigation of individual rain droplets are given. Analytical methods for a sampling procedure as well as analysis in the ultra trace level with volumes less than 1 l have been developed. Because of the small volumes chromatographic methods are to be preferred.     

Apparent Molar Volumes of Proline-Leucine Dipeptide in NaCl Aqueous Solutions at 318.15 K

Density measurements of pseudo-binary solutions of proline-leucine dipeptide in aqueous NaCl solutions with molality ranging from 0 to 1 mol-kg^–1 have been performed at 318.15 K. Apparent molar volumes, V_{, 2}, of proline-leucine were calculated from the measured data. Limiting partial molar volumes, V₂, and limiting partial molar volumes of transfer from water to aqueous NaCl solutions, _tr V₂, were derived and interpreted in terms of ion-dipeptide interactions and changes in the characteristics of the hydration shell around the biomolecules as well.     

Effect of pressure on the solubilities ofo-,m- andp-xylene in water

The solubilities of o-, m- and p-xylene in water were measured at 25.0°C up to 250, 385, and 50 MPa, respectively. The solubility increased with increasing pressure up to 120 MPa (50 MPa for p-xylene) and then decreased. The reaction volumes, V^o accompanying the dissolution at 0.1 MPa were estimated as –3.6±0.5, –3.4±0.5, and –4.1±0.5 cm³-mol^–1 for o-, m-, and p-xylene, respectively, from the pressure dependences of the solubilities. The limiting partial molar volumes, of p- and o-xylene in water under high pressure were estimated from V^o and the molar volume of the xylene. The partial molar volumes decreased with increasing pressure. The reaction volume for the formation of intra-molecular pairwise hydrophobic interaction between the methyl groups, as proposed by Ben-Naim, is discussed for the V^o of p- and o-xylene at 0.1 MPa.     

Ion solvation in lithium battery electrolyte solutions. 1. Apparent molar volumes

Apparent molar volumes, V(MX), of seven electrolytes (NaClO₄, NaCF₃SO₃, NaBPh₄, LiClO₄, LiAsF₆, Ph₄AsCF₃SO₃ and KCF₃SO₃) have been determined by vibrating-tube densimetry in nonaqueous solvent mixtures of propylene carbonate (PC) with acetonitrile (AN), dimethoxyethane (DME) and tetrahydrofuran (THF). V(MX) was measured at an electrolyte concentration of 0.05M over the entire solvent composition range wherever possible. Ionic apparent molar volumes of transfer, _tV(ion), were obtained via the tetraphenylarsonium tetraphenylborate (TATB) assumption. _tV(ion) from PC to the mixed solvents are generally strongly negative for both cations and anions consistent with the greater compressibilities and lower dielectric constants of the cosolvents. In PC/AN mixtures cations and anions have similar values of _tV(ion) but in PC/DME and PC/THF mixtures they differ considerably. Cationic volumes show the expected dependence on ion-size but the differences among the anion volumes are much greater than expected at high cosolvent compositions. These effects are discussed in terms of preferential solvation and other solvent interactions. The implications of these findings for lithium batteries are briefly discussed.     

Analyses of hazardous substances in biological materials

Summary The interest of the Commission for the Investigation of Health Hazards of Chemical Compounds in Work Area of the German Science Foundation in practical, sensitive and specific methods for monitoring the limit values led to the establishment of the working group Analytical Chemistry in 1969. A loose-leaf collection Analysen in biologischem Material and 3 volumes of an English edition have since been published. In the meantime the German edition of Analyses in biological materials has been supplemented ten times, including 100 methods for the measurement of about 170 parameters; the English edition is in 3 volumes with 45 selected methods. The volumes include only standard operational procedures that are suitable for routine use. The reliability of the analytical procedures is defined and checked for these reasons and because they satisfy the requirements of statistical quality control. The analytical methods published by the Working Group Analytical Chemistry are recommended by pertinent guidelines and regulations for use in Germany.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Volumetric Properties of Binary Mixtures of Acetonitrile and Chloroalkanes at 25°C and Atmospheric Pressure

Excess molar volumes for binary mixtures of acetonitrile + dichloromethane, acetonitrile + trichloromethane, and acetonitrile + tetracloromethane at 25°C have been used to calculate partial molar volumes , excess partial molar volumes , and apparent molar volumes of each component as a function of composition. The V _m ^Evalues are negative over the entire composition range for the systems studied. The applicability of the Prigogine–Flory–Patterson theory was explored. The agreement between theoretical and experimental results is satisfactory for the systems with dichloromethane and tetrachloromethane. For the unsymmetrical behavior of the system with trichloromethane, however, the agreement is poor.     

Chromatography of diols. Regularities in the retention of linear diprimary diols in gas-solid and gas-liquid chromatography

Summary Using various sorbents in gas-liquid chromatography and gas-solid chromatography, the dependence of the retention of diprimary linear diols of the HOCH₂(CH₂)_nCH₂–OH type (n=0–4) on different parameters characterizing the physicochemical properties of the diols was studied. As shown, the relationship between the logarithm of the retention volume, or the boiling point, molecular mass, number of CH₂-groups, density, refractive index, molecular refraction, and the logarithm of the retention volumes obtained on another stationary phase is either linear or nearly linear. The linear regression coefficients of the various relationships are given.A change in the free adsorption energy (F) of the diols on Polysorb, Tween and polyethylene glycol 2000 with respect to ethylene glycols was studied. It is shown that Polysorb appeared to be the most specific stationary phase.Nauchno-proizvodstvennoe ob'edunenie (Research-industrial Company), Olajne, USSR.     

Volumes and heat capacities of water andN-methylformamide in mixtures of these solvents

The densities of mixtures ofN-methylformamide (NMF) and water (W) have been measured at 5, 15, 25, 35, and 45°C, and the heat capacities of the same system at 25°C, both over the whole mole-fraction range. From the experimental data the apparent molar volumes (_v) and heat capacities (_c) of NMF and of water are evaluated. The relatively small difference between the partial molar volumes or heat capacities at infinite dilution and the corresponding molar volumes or heat capacities of the pure liquids for both NMF and water suggests that with regard to these quantities replacement of a NMF molecule by a water molecule or vice versa produces no drastic changes. The partial molar volume of water at infinite dilution in NMF is smaller than the molar volume of pure water, but the corresponding partial molar heat capacity is unexpectedly high.     

Determination of Total Organic Sulfur in Petroleum Products

A procedure was proposed for determining total organic sulfur in petroleum products. The procedure involves the exhaustive hydrogenolysis of sulfur-containing compounds in an autonomous quartz flow reactor under a hydrogen atmosphere at 1000 ± 50°C with the trapping of the hydrogen sulfide formed in an aqueous solution of an alkali followed by the gas-chromatographic determination of H₂S in the trapping solution using dynamic reaction gas extraction and selective flame-photometric detection. The determination limit was 0.01 wt % for sample volumes below 30 L; the relative standard deviation was 7% on average.     

Solvent Effect on the Partial Molar Volume and the Enthalpy of Solution of Gallium Chloride

Partial molar volumes and heats of solution were determined for gallium chloride in benzene, toluene, o-xylene, mesitylene, 1,2-dichloroethane, ethyl acetate, acetonitrile, and 1,4-dioxane. A proportionality in changes in these characteristics is observed for weak ,-type complexes in alkylbenzene medium. The partial molar volumes of strong n,-type complexes approach a limiting value.     

The true physical meaning of the corrected retention volumes in GC

Summary Through a straightforward mathematical derivation it is shown that the compressibility correction factor equals the ratio of gas pressure at the column outlet to the average pressure in the column, . Therefore, by multiplying by this factor, the experimentally measured retention volumes can be recalculated to the average pressure in the column. Corrected retention volumes thus represent the volume of the mobile phase under real conditions of chromatography in the column. Appropriate definitions for corrected retention volumes and factorj are formulated.     

Gas chromatography on a self-associating component of a binary phase. Retention model by formal analogy with conductance of electrolytes in dilute solution

Summary The dependence of specific retention by a binary stationary phase in GC can be expressed as the sum of the products of the specific retention of the pure components times their respective volume fractions. In this study, however, one component has a site, which is not only mainly responsible for the selectivity, but also participates in strong self-association. This requires introduction of a concentration-dependent factor (^x) in the corresponding term of the equation correlating Vg _mix ^x with x. In the GC resolution of N-trifluoroacetyl-amino acid isopropyl esters on a binary phase, N-lauroyl-L-amino t-butyl amide-squalane, data for the values of ^x were obtained.Adapting a previously developed LC retention model to the above GC data, an equation was derived for the dependence of ^x on the weight fraction (x) of the selector, namely ^x=1/x. This relationship permits calculation of retention volumes on the binary phase for a given x, as well as corresponding resolution coefficients of enantiomeric amino acid derivatives with generally excellent agreement with experiment. The chirality of the system is not relevant to application of the equation.     

Ionization volumes by means of direct dilatometry

A rapid and convenient new technique is described to determine ionization volumes directly by means of dilatometry. In this method, acid and base solutions of appropriate strength are stacked and mixed after an initial reading is made. Each solution is also treated similarly with solvent alone. The ionization volumes of water and of several weak acids and bases in water have been calculated from the data. They generally compare quite well with literature values determined by more elaborate means; several new results are also reported.