Stationary phases McReynolds’ phase constants

In a series of papers published throughout the 1980s, Colin Poole and his co-workers investigated the solvation properties of a wide range of alkylammonium and, to a lesser extent, phosphonium salts. Parameters such as McReynolds phase constants were calculated by using the ionic liquids as stationary phases for gas chromatography and analysis of the retention of a variety of probe compounds. However, these analyses were found to be unsatisfactory and were abandoned in favour of an analysis that used Abraham s solvation parameter model [5]. 

McReynolds phase constants Developed to establish a systematic ordering of GC stationary phases with respect to specific solute interactions. This can then be used to predict the change in the retention index, AI, for the tested phase with respect to squalene ... 

Table 11.13 McReynolds Constants for Stationary Phases in Gas Chromatography...

Similar stationary phases Temp., °C McReynolds constants USP code... 

Solvent selectivity is a measure of the relative capacity of a solvent to enter into specific solute-solvent interactions, characterized as dispersion, induction, orientation and coaplexation interactions, unfortunately, fundamental aiq>roaches have not advanced to the point where an exact model can be put forward to describe the principal intermolecular forces between complex molecules. Chromatograidters, therefore, have come to rely on empirical models to estimate the solvent selectivity of stationary phases. The Rohrschneider/McReynolds system of phase constants [6,15,318,327,328,380,397,401-403], solubility... 

More experienced chromatographers may refer to the McReynolds constants for a given stationary phase as a measure of its resolving power. A complete discussion of this subject, however, is beyond the scope of this text. 

McReynolds constants constitute a classification system for GLC stationary phases based on their polarity ... 

McReynolds used the retention index of certain solutes to compare different stationary phases and to assess their selectivity compared with a reference liquid phase, squalane. Squalane is considered to be non-polar and any increase in the retention index of the selected solute on the test column compared to squalane may be considered to be due to the greater polarity of that solvent. McReynolds constants have been determined for all stationary phases using a range of solutes of varying polarity (Table 3.8) and may be used to assist in selecting an appropriate stationary phase. 

In GLC, if a stationary phase with a low value McReynolds constant is used which of the following will be eluted quickly from the column ... 

GC phase increases. A measure of the polarity of a stationary phase is given by its McReynold s constant (Table 11.1), which is based on the retention times of benzene, n-butanol, pentan-2-one, nitropropane and pyridine on a particular phase. The higher the McReynold s constant the more polar the phase. Many stationary phases are described by an OV-number. The higher the number after the OV the more polar the phase. 

The five McReynolds constants for a given stationary phase are obtained by calculating the differences between Kovats indices obtained on squalane (/squaiane) and those obtained on the stationary phase being studied (/phase)-... 

These constants, which are related to the structure of the molecules, allow an evaluation of the forces of interaction between the stationary phase and the solute for different classes of compounds. An index with an elevated value indicates that the stationary phase has a strong affinity for compounds that contain particular organic functions. This leads to a greater selectivity for this type of compound. For example, in order to separate an aromatic hydrocarbon contained in a mixture of ketones, a stationary phase for which benzenes have a very different constant than butanone will be selected. These differences in indices appear in most manufacturers catalogues of chromatographic components (Table 2.1). McReynolds constants have more or less replaced Rohrschneider constants, which are based on the same principle but use different reference compounds. 

Table 2.1—McReynolds constants (AT) for several stationary phases...

These Al values are listed as in Table 3.2, where the x, y, z, u, and s values indicate the polarity of the phases for each type of compound. Most chromatography supply catalogs now contain these "McReynolds constants" for the stationary phases offered for sale. 

Haken has considered the applicability of "Rohrschneider/ McReynolds constants" for the classification of stationary phases for the separation of fatty esters (13). He concluded that the approach was limited since the measurements used to determine the aforementioned "constants" are made at 100°C and most fatty acid methyl ester separations are carried out at about 200°C. He had previously shown significant variation in the, what will now be called, Rohrschneider/McReynolds coefficients, with temperature (14). Polar polysiloxanes such as XF-1150 demonstrated greatest variability in the coefficients and nonpolar types such as SE-30 demonstrated least variation. Supina pointed out that the X factor in the McReynolds coefficients should be indicative of extent of interaction with olefinic substituents (15). Figure 9.5 demonstrates the utility of this approach the 18 3 and 20 0 methyl esters are used as markers for the consideration of... 

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