Enhance Retention of Sulfur Containing Compounds Through Pi-Pi Interactions Using Pinnacle DB Biphenyl HPLC Columns

Pharmaceutical actives and impurities often contain sulfur in the form of a sulfone or sulfoxide group. Both groups have dipole moments, adding a hydrophilic character to compounds containing these functional groups. The analysis of hydrophilic compounds on traditional alkyl columns (e.g. C18) can be problematic, since alkyl columns depend on hydrophobic interactions for retention. Since the sulfone and sulfoxide groups contain π-π bonds, the biphenyl column's ability to undergo π-π interactions makes it an excellent choice when increased retention or selectivity of compounds containing these groups is desired. To demonstrate the selectivity of the biphenyl phase towards aromatic compounds containing sulfur groups, a set of target compounds was selected and analyzed on C18, phenyl, and biphenyl columns.

Figure 1

Results and Conclusions

Of the compounds analyzed, tenoxicam and sulfinpyrazone contain sulfur in the form of a sulfone and a sulfoxide group, respectively. The Pinnacle™ DB Biphenyl column exhibited improved retention for both compounds. With k' values of 0.41 on the C18 and 0.61 on the phenyl columns, tenoxicam shows almost no retention on these stationary phases. However, when these probes were analyzed on the biphenyl column under the same conditions, the k' of tenoxicam increased to 2.73. Sulfinpyrazone followed the same pattern, with its k' value increasing six-fold from 2.29 on the C18 column to 15.29 on Pinnacle™ DB Biphenyl column (Figure 1). The improved retention for tenoxicam and sulfinpyrazone is due to the unique retention mechanism of the biphenyl stationary phase, which takes advantage of the π-π bonds in sulfone and sulfoxide groups.

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