Memory Effects of Mobile Phase Additives on the Whelk-O®1 Chiral Phase

February 1, 2009
Ted Szczerba

Regis Technologies, Inc.

The Application Notebook

The Application Notebook, The Application Notebook-02-01-2009, Volume 0, Issue 0

The Pirkle - Type Whelk-O®1 CSP is a synthetically made chiral selector covalently bonded to a silica support. This phase is well known in the industry for its broad degree of generality, mobile phase compatibility, and ability to invert elution order. Most commonly used polysaccharide coated CSP's are sensitive to the presence of certain mobile phase modifiers such as DEA, TEA, and TFA. Retained memory effects can adversely affect a separation resulting in broad and tailing peaks, no peak elution, and reduced or loss of separation altogether. To remove these unwanted memory effects, the column must be rinsed with an alcohol, such as methanol or ethanol. This is a time consuming and costly process. The Whelk-O®1 CSP does not exhibit any such retained memory behavior.

The Pirkle - Type Whelk-O® 1 CSP is a synthetically made chiral selector covalently bonded to a silica support. This phase is well known in the industry for its broad degree of generality, mobile phase compatibility, and ability to invert elution order. Most commonly used polysaccharide coated CSP's are sensitive to the presence of certain mobile phase modifiers such as DEA, TEA, and TFA. Retained memory effects can adversely affect a separation resulting in broad and tailing peaks, no peak elution, and reduced or loss of separation altogether. To remove these unwanted memory effects, the column must be rinsed with an alcohol, such as methanol or ethanol. This is a time consuming and costly process. The Whelk-O®> 1 CSP does not exhibit any such retained memory behavior.

A study was performed using Carprofen as the test analyte, employing four different mobile phase modifiers (Acetic acid, TFA, DEA, and TEA). The runs were carried out under identical mobile phase composition on a Whelk-O®> 1 column. There were no column washes between the runs. Following are the results.

Table I Summary

Column: (S,S)Whelk-O®> 1, 5 micron Kromasil, 25 cm × 4.6 mm

Sample: Carprofen

Mobile Phase: Hexane/Ethanol (75/25)

+ Modifier

Flow Rate: 1.5 mL/min

Table 1

Conclusion

From the chromatograms listed, it is evident that mobile phase modifiers do alter chromatographic separations. Table I lists capacity factors and selectivity data for various modifiers. The data demonstrates that exposures to different mobile phase additives retains no memory effects on the Whelk-O®> 1 column. Different modifiers can be used on Whelk-O®> 1 without altering the performance of the column or needing a reconditioning procedure.

Figure 1

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