Polarity index Solvent

Polarity Index Solvent Viscosity CP (20°) Boiling Point (°C, 760 Torr) Miscibility Number (M)... 

Solvent Polarity Index Solvent Polarity Index... 

Choosing a Mobile Phase Several indices have been developed to assist in selecting a mobile phase, the most useful of which is the polarity index. Table 12.3 provides values for the polarity index, P, of several commonly used mobile phases, in which larger values of P correspond to more polar solvents. Mobile phases of intermediate polarity can be fashioned by mixing together two or more of the mobile phases in Table 12.3. For example, a binary mobile phase made by combining solvents A and B has a polarity index, of... 

Changing the mobile phase s polarity index, by changing the relative amounts of two solvents, provides a means of changing a solute s capacity factor. Such... 

Solvent strength determines the value, but not the selectivity. The mobile phase can be established by using the polarity index P proposed by Snyder. The highest values of P represent the strongest solute adsorbed in conventional TLC but represent the weakest for the separation in reversed phases. Sometimes aqueous polar mixtures cannot totally wet the chemically bonded layer. For this reason, checking... 

The model has the advantage that it requires only a simple table eontaining the polarity index P and selectivity group for a number of solvents (Table 4.2). The model is based on Snyder s elassifieation of solvents [41,42] aeeording to their eharaeteristies to internet as proton aeeeptors (xj, proton donors (x, or dipoles (xj. 

Solvent Polarity index Solubility in water (%, w/w) Density (gmL-i) Viscosity (mN s Expansion volume Boiling point (°C)... 

The polarity index is a measure of the polarity of the solvent, which is often the most important factor in the solvent choice for the particular application. In extraction processes, the tenet that like dissolves like (and conversely, opposites do not attract ) is the primary consideration in choosing the solvent for extraction, partitioning, and/or analytical conditions. For example, hexane often provides a selective extraction for nonpolar analytes, and toluene may provide more selectivity for aromatic analytes. 

However, not withstanding the above objections, further discussion of the Snyder solvent triangle classification method is justified by its common use in many solvent optimization schemes in liquid chromatography. The polarity index, P, is given by the sum of the logarithms of the polar distribution constants for ethanol, dioxane and nltromethane and the selectivity parameters, X, as the ratio of the polar distribution constant for solute i to... 

The solvent triangle classification method of Snyder Is the most cosDBon approach to solvent characterization used by chromatographers (510,517). The solvent polarity index, P, and solvent selectivity factors, X), which characterize the relative importemce of orientation and proton donor/acceptor interactions to the total polarity, were based on Rohrscbneider s compilation of experimental gas-liquid distribution constants for a number of test solutes in 75 common, volatile solvents. Snyder chose the solutes nitromethane, ethanol and dloxane as probes for a solvent s capacity for orientation, proton acceptor and proton donor capacity, respectively. The influence of solute molecular size, solute/solvent dispersion interactions, and solute/solvent induction interactions as a result of solvent polarizability were subtracted from the experimental distribution constants first multiplying the experimental distribution constant by the solvent molar volume and thm referencing this quantity to the value calculated for a hypothetical n-alkane with a molar volume identical to the test solute. Each value was then corrected empirically to give a value of zero for the polar distribution constant of the test solutes for saturated hydrocarbon solvents. These residual, values were supposed to arise from inductive and... 

Another measure of polarity, the polarity index, P, is calculated from solubility data. This quantity again increases with increasing polarity. Fig. 3.If shows the values of both of these quantities for a range of solvents, in order of increasing P. The order of polarity is... 

Fig. 3.1f. Solubility parameter and polarity index for a range of solvents...

Linear absorption and fluorescence spectra for the series of symmetrical cationic polymethines with 5-butyl-7,8-dihydrobenzo[ /]furo 2,3 /lindolium terminal groups are shown in Fig. 14 for solvents of different polarity. It is known that the polarity of solvents can be characterized by their orientational polarizability, which is given by Af = (e- l)/(2e + 1) — (n2 - l )/(2n2 +1), where e is the static dielectric constant and n is the refractive index of the solvent [41], Calculated A/values... 

Grathwohl (1990) found a relationship between sorption capacity and the the atomic H/O ratio of NOM. Similarly, there is a good relationship between log Koc and the polarity index (PI) of SOM, defined as the (0+N)/C ratio (DePaolis and Kukkonen 1997 Rutherford et al. 1992 Xing 1997 Xing et al. 1994a). The effect of SOM polarity on sorption of organic compounds is consistent with the well-known theory of solvent polarity on solute solubility. In studying the influence of SOM composition... 

The P (polarity index) values and selectivity group classifications for some solvents commonly used in LC are given in Table 15.15. 

White or colorless crystalline solid (nonahydrate - rhombic crystal) deliquescent refractive index 1.54 melts at 73.5°C decomposes at 150°C highly soluble in cold water (63.7% at 25°C), decomposes in hot water, soluble in polar organic solvents. 

Liquids with equal solubility parameters are miscible, there is no heat of mixing. With increasing difference of <5, two phases coexist, which become miscible at elevated temperature, at the critical consolute temperature Tc. Tc increases with the difference of the <5 s and with the mean molar volume of the two liquids. Another polarity scale was recently introduced by Middleton and co-workers13 based on the bathochromic shift of UV-visible 2max. The obtained spectral polarity index ranks the solvents at one end of the scale is the nonpolar perfluorohexane and at the opposite the highly polar and acidic l,l,2,3,3.3-hexafluoropropan-2-ol. The latter is much more polar than its hydrocarbon analog. 

Of the many empirical polarity parameters or indexes that have been proposed, only a few remain viable, in the sense that they are currently more or less widely used to describe the polarity of solvents for various purposes. Some such parameters that are commonly used describe better other, more specific, properties than polarity e.g., hydrogen bond or electron-pair donation ability. Thus, only two polarity parameters have been employed in recent years Dimroth and Reichardt s A T(30) (Dimroth et al. 

Besides substance lipophilicity, the polarity of the organic solvent also determines extraction efficiency premising sufficient solubility. Polarity of liquids can be characterized by the Snyder polarity index (P ) sorting solvents from smallest polarity (pentane, P O), over small (methyl-ferf-butyl ether, MTBE, P 2.5 diethylether, Et20 P 2.8 dichloromethane P 3.1), and medium (chloroform P 4.1 ethylacetate, EE P 4.4) to high polarity (dimethylsulfoxide, DMSO P 7.2 water P 10.2) [91]. 

This polarity index measures the intermolecular attraction between a solute and a solvent, whereas the Hildebrand solubility parameter is defined for pure solvent. For example, ether is not very polar and has a Hildebrand value of 7.4—about the same as hexane, which has a value of 7.3. However, ether can accept protons in the form of hydrogen bonds to its nonbonding electron pairs, and consequently its polarity index is 2.8 compared to 0.1 for hexane. 

TABLE 15 Polarity Index and Values for Molecular Interactions for Some Solvents... 

Table 11.3 Ultraviolet Cutoff Wavelength Ac (at which the Solvent in a Cell of Path Length L = 1 cm has an Absorbance of 1 unit). Dielectric Constant e, Scalar Refractive Index nD (Measured at 589 nm, the Na D-line), Dipole Moment ft (Debyes30), and Reichardt s31 Solvent Polarity Index ET...

The aforementioned macroscopic physical constants of solvents have usually been determined experimentally. However, various attempts have been made to calculate bulk properties of Hquids from pure theory. By means of quantum chemical methods, it is possible to calculate some thermodynamic properties e.g. molar heat capacities and viscosities) of simple molecular Hquids without specific solvent/solvent interactions [207]. A quantitative structure-property relationship treatment of normal boiling points, using the so-called CODESS A technique i.e. comprehensive descriptors for structural and statistical analysis), leads to a four-parameter equation with physically significant molecular descriptors, allowing rather accurate predictions of the normal boiling points of structurally diverse organic liquids [208]. Based solely on the molecular structure of solvent molecules, a non-empirical solvent polarity index, called the first-order valence molecular connectivity index, has been proposed [137]. These purely calculated solvent polarity parameters correlate fairly well with some corresponding physical properties of the solvents [137]. 

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