Ionic volumes method

Styrene-Divinylbenzene Networks. Using ionic polymerization methods, Rietsch et al. (1976) prepared polystyrene (PS) networks with a well-controlled length of elastically active chains and crosslinks of variable functionality. In a given series, the glass transition temperature obeys the classical free volume theory ... 

The interfacial tension methods are described in ISO 6889 [20], ISO 9101 [21] and ASTM D1331 -89 (2001) [ 18 ]. The method described in ISO 6889 is a simple method and applicable for the systems if the interfacial values arebetween 4 and 50 dyne cm-1, the immiscible liquids are water and organic liquids and the systems contain non-ionic or anionic surfactants but not cationic surfactants. The repeatability is within about 2 dyne cm-1. On the other hand, the drop volume method as described in ISO 9101 can be used for viscous liquids and liquids containing all types of surfactants. This method can measure the interfacial tension as low as 1 dyne cm-1 with 0.5 dyne cm-1 accuracy. If the interfacial tension is lower than 1 dyne cm-1, the spinning drop will be the suitable method. 

Conway has suggested a method that seems to give results in agreement with those of a second entirely different method, the ionic vibration method (see later discussion). Conway found that plotting the partial molar volume of a series of electrolytes involving large cations (e.g., a tetraalkylammonium series) and a constant smaller... 

Figure 1.31 gives one example of a comparison between results from two different techniques, applied to one and the same system. In this case the (rton-ionic) surfactant was specially synthesized and well-defined p-tert.butylphenol with 10 EO groups. It is seen that the results of the (faster) maximum bubble technique and the (slower) drop volume method, connect well. Many more... 

In finite-volume methods, the integral formulation of the conservation laws over a small physical control volume is discretized directly. FVM employs a conservative discretization, that is, each species is guaranteed to be conserved, even for coarse meshes. In contrast, many traditional FDMs are not conservative. For example, owing to the nonlinear nature of the constitutive flux equations of ionic species in an a priori unknown electric field, FDM is nonconservative, even when constant physical... 

Millcro has also used the correspondence principle method to evaluate ionic volumes in NMP as well as in methanol. Similar to the case for entropies, ionic volumes in the non-aqueous system are plotted against the absolute 5n(aq) values, and the Vi (X) for the non-aqueous system assigned so that values for both cations and anions fall on the same line. The volumes can be expressed, similar to eqn. 2.11.36, as... 

Cox and Wolfenden suggested a method based on absolute ionic mobilities, which can be experimentally determined. They observed that the temperature coefficient of mobility of the lithium and iodate ions conforms with Stokes law, inasmuch as the variation of the fluidity of the solvent with temperature is expected to affect the mobility of an ion. As a consequence of this they reasoned that ion is proportional to the ionic volume, and by making the division in the required ratio arrived at a value for of 0.14e, from which the other values can be immediately obtained. 

Despite this drawback there is an interest in science and technology in single-ion quantities for rationalizing the discussion of electrolyte solution properties. Various methods have been developed for their estimation based on extrathermodynamic assumptions, such as the following (1) The contributions of cation and anion are set equal for a salt composed of ions of equal charge and approximately equal radii (2) the results of measurements on a series of homologous electrolytes are extrapolated with regard to ionic radii or ionic volumes to zero ion size or zero reciprocal radii (3) the differences in conventional ionic properties are used for theoretically rationalized extrapolations and (4) the properties of ions are compared with those of isoelectronic neutral molecules of similar chemical constitution and size. 

Microscopic ionic volumes of RTILs, the sums of the constituent 20 cations and 20 anions Vj = v+ + v, were calculated by several theoretical methods according to Preiss et al. [49] and compared with the crystal volumes obtained from x-ray diffraction (Table 2.4). It was then shown that several physical properties were linear with these microscopic volumes the molar volume V, the isobaric expansibility ap, the molar heat capacity Cp, the (logarithm of) the viscosity In , and the (logarithm of) the molar conductivity InA all these obey the relation a + bv. ... 

The influence of temperature, solution s pH and other parameters in formation of ionic associate is investigated. As a result, optimal conditions of determination are established pH 4,0 volume of acetate buffer - 0,5 ml volume of 0,1% aqueous solution of CV - 0,3 ml extraction time - 3 minutes. The ratio of aqueous and organic phases is 1 1. Photometric measurement of toluene layer is carried out at = 606,0 nm. The accuracy of procedures checked by the method of additives. 

Tailing peaks or longer than expected elution volumes are sometimes caused by low solubility of the protein in the mobile phase. Using a trial-and-error process, select the proper pFf and ionic strength to address this problem. Detergents such as sodium dodecyl sulfate (SDS) are sometimes helpful but, because they change the conformation of many proteins and are difficult to remove from the column should be used only if other methods fail. 

In the development of a SE-HPLC method the variables that may be manipulated and optimized are the column (matrix type, particle and pore size, and physical dimension), buffer system (type and ionic strength), pH, and solubility additives (e.g., organic solvents, detergents). Once a column and mobile phase system have been selected the system parameters of protein load (amount of material and volume) and flow rate should also be optimized. A beneficial approach to the development of a SE-HPLC method is to optimize the multiple variables by the use of statistical experimental design. Also, information about the physical and chemical properties such as pH or ionic strength, solubility, and especially conditions that promote aggregation can be applied to the development of a SE-HPLC assay. Typical problems encountered during the development of a SE-HPLC assay are protein insolubility and column stationary phase... 

The simplest method to measure gas solubilities is what we will call the stoichiometric technique. It can be done either at constant pressure or with a constant volume of gas. For the constant pressure technique, a given mass of IL is brought into contact with the gas at a fixed pressure. The liquid is stirred vigorously to enhance mass transfer and to allow approach to equilibrium. The total volume of gas delivered to the system (minus the vapor space) is used to determine the solubility. If the experiments are performed at pressures sufficiently high that the ideal gas law does not apply, then accurate equations of state can be employed to convert the volume of gas into moles. For the constant volume technique, a loiown volume of gas is brought into contact with the stirred ionic liquid sample. Once equilibrium is reached, the pressure is noted, and the solubility is determined as before. The effect of temperature (and thus enthalpies and entropies) can be determined by repetition of the experiment at multiple temperatures. 

Ion chromatography (see Section 7.4). Conductivity cells can be coupled to ion chromatographic systems to provide a sensitive method for measuring ionic concentrations in the eluate. To achieve this end, special micro-conductivity cells have been developed of a flow-through pattern and placed in a thermostatted enclosure a typical cell may contain a volume of about 1.5 /iL and have a cell constant of approximately 15 cm-1. It is claimed15 that sensitivity is improved by use of a bipolar square-wave pulsed current which reduces polarisation and capacitance effects, and the changes in conductivity caused by the heating effect of the current (see Refs 16, 17). 

Returning to the molecular force concept, in any particular distribution system it is rare that only one type of interaction is present and if this occurs, it will certainly be dispersive in nature. Polar interactions are always accompanied by dispersive interactions and ionic interactions will, in all probability, be accompanied by both polar and dispersive interactions. However, as shown by equation (11), it is not merely the magnitude of the interacting forces between the solute and the stationary phase that will control the extent of retention, but also the amount of stationary phase present in the system and its accessibility to the solutes. This leads to the next method of retention control, and that is the volume of stationary phase available to the solute. 

Stability may be inherent or induced. In the latter case, the original system is in a condition of metastable or neutral eouilibrium. External influences which induce instability in a dispersion on standing are changes in temperature, volume, concentration, chemical composition, and sediment volume. Applied external influences consist of shear, introduction of a third component, and compaction of the sediment. Interfacial energy between solid and liquid must be minimized, if a dispersion is to be truly stable. Two complementary stabilizing techniques are ionic and steric protection of the dispersed phase. The most fruitful approach to the prediction of physical stability is by electrical methods. Sediment volumes bear a close relation to repulsion of particles for each other. 

During electrolysis there is no change in composition of an individual melt close to the electrode surfaces only its quantity (volume) will change. The resulting void space is filled again by flow of the entire liquid melt mass. This flow replaces the diffusional transport of ions customarily associated with aqueous solutions. This has particular consequences for the method used to measure ionic transport numbers ... 

Capillary electrophoresis offers several useful methods for (i) fast, highly efficient separations of ionic species (ii) fast separations of macromolecules (biopolymers) and (iii) development of small volume separations-based sensors. The very low-solvent flow (l-10nL min-1) CE technique, which is capable of providing exceptional separation efficiencies, places great demands on injection, detection and the other processes involved. The total volume of the capillaries typically used in CE is a few microlitres. CE instrumentation must deliver nL volumes reproducibly every time. The peak width of an analyte obtained from an electropherogram depends not only on the bandwidth of the analyte in the capillary but also on the migration rate of the analyte. 

Parameters that should be tested in HPLC method development are flow rate, column temperature, batch and supplier of the column, injection volume, mobile phase composition and buffer pH, and detection wavelength [2], For GC/GLC methods, one should investigate the effects of column temperature, mobile phase flow rate, and column lots or suppliers [38], For capillary electrophoresis, changes in temperature, buffer pH, ionic strength, buffer concentrations, detector wavelength, rinse times, and capillaries lots and supplier should be studied [35, 36], Typical variation such as extraction time, and stability of the analytical solution should be also evaluated [37],... 

Marcantoncetos et al. [112] have described a phosphorimetric method for the determination of traces of boron in seawater. This method is based on the observation that in the glass formed by ethyl ether containing 8% of sulfuric acid at 77 K, boric acid gives luminescent complexes with dibenzoylmethane. A 0.5 ml sample is diluted with 10 ml 96% sulfuric acid, and to 0.05-0.3 ml of this solution 0.1ml 0.04 M dibenzoylmethane in 96% sulfuric acid is added. The solution is diluted to 0.4 ml with 96% sulfuric acid, heated at 70 °C for 1 h, cooled, ethyl ether added in small portions to give a total volume of 5 ml, and the emission measured at 77 K at 508 nm, with excitation at 402 nm. At the level of 22 ng boron per ml, hundredfold excesses of 33 ionic species give errors of less than 10%. However, tungsten and molybdenum both interfere. 

A second approach is the standard addition method, which is commonly employed when the sample is unknown. The potential of the electrode is measured before and after addition of a small volume of a standard to the known volume of the sample. The small volume is used to minimize the dilution effect. The change in the response is related only to the change in the activity of the primary ion. This method is based on the assumptions that the addition does not alter the ionic strength and the activity coefficient of the analyte. It also assumes that the added standard does not significantly change the junction potential. 

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