HPLC Separation of Benzenesulfonic and p-Toluenesulfonic Acids


Benzenesulfonic and toluenesulfonic acids are organic acids used in pharmaceutical industry as counter-ions for basic drugs. Both acids are hydrophilic in nature with strong acidic properties. Obtaining separation, retention and good peak shape with traditional reversed-phase columns is a challenging task. We developed robust mixed-mode approach for separation of benzenesulfonic acid and p-toluenesulfonic acid on a Primesep D reversed-phase anion-exchange column. Elution of these compounds is controlled by the amount of ions in the mobile phase and amount of acetonitrile. Both compounds are separated within 4 minutes and can be monitored by UV, ELSD, CAD or LC/MS. This column can be also used to analyze hydrophobic basic drugs by reversed-phase cation-exclusion mechanisms.