Simultaneous Analysis of Active Pharmaceutical Ingredients and Their Counter-Ions Using a Mixed-Mode Column

Approximately 50 % of all drug molecules used in pharmaceutical products are reported to be ionic compounds. Ion chromatography is generally appropriate to analyze inorganic or organic ions, but not suitable for active pharmaceutical ingredients (APIs) analysis due to their hydrophobicity. On the other hand, reversed phase liquid chromatography (RPLC) is mainly applied for analysis of APIs, but cannot retain commonly-used ions for drugs. Consequently, it is difficult to analyze APIs and their counter-ions simultaneously.
In this study, we evaluated the ReDual column, our newly-developed mixed-mode column, for simultaneous analysis of APIs and their counter-ions. Mixed-mode column usage has increased because of the ability to analyze a wide range of compounds in a single run by multimode retention mechanisms. First, we investigated how retention behavior changes with parameters such as concentration of organic solvents, ion strength, and pH of the mobile phase using the ReDual CX-C18 mixed-mode column. Secondly, we analyzed naproxen sodium and potassium clavulanate. They were successfully analyzed on the column just by changing mixing ratio of the mobile phase.