McReynold constant

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

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

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. 

Liquid phase Example McReynolds constants for selected test compounds... 

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 ... 

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)-... 

Assuming that the following Kovats indices are found for a column containing polypropyleneglycol benzene = 775 and pyridine = 918, the McReynolds constants... 

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. 

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