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Abstract
Ion interaction chromatography has been demonstrated to be a viable separation scheme for a wide variety of small molecules. This separation mechanism has been shown to be effective for a complex mixture of analytes that range from uncharged to positively and/or negatively charged. The analytes present in fexofenadine‐D tablets are either uncharged or cationic. Therefore, if a single HPLC method is to be used for this difficult separation, a dual mechanistic system must be present so that the charged and neutral components are retained and separated. An ion interaction liquid chromatographic system that contains an anionic surfactant, such as sodium dodecyl sulfate (SDS), meets both of these requirements: a reversed stationary phase for a hydrophobic analyte and a fixed anionic charge site for a positively charged analyte. The effect that each mobile phase parameter may have on this complex separation was found to be crucial. These variables were studied and include: concentration of SDS, ionic strength, pH, concentration of phosphoric acid, concentration of organic modifier, column temperature, and different gradients. The results obtained in this study and the optimized separation is discussed.