Modeling of Ibuprofen II: Effect of pH on the Adsorption Behavior on Reversed Phase Liquid Chromatography
Tarab Ahmad, Bobilla Srihari, Bakheet Alresheedi, Netkal Made Gowda

Abstract
The present work involves the study of the influence of pH on the adsorption behavior of ibuprofen on reversed phase liquid chromatography (RPLC). The following four different mobile phases were used for this study at three different pH values: 40% acetonitrile at pH 2.5, 4.38 and 6.72 and 30% acetonitrile at pH 6.5. The adsorption isotherms of ibuprofen are determined by the frontal analysis method and by the inverse method of determining the isotherm. Our results indicate that the adsorption of ibuprofen follows a bi-Langmuir model for the mobile phase containing 40%ACN and at pH 2.5 which is below the pKa value of ibuprofen, while the adsorption pattern follows a bi-Moreau model when mobile phases containing 40% ACN at pH 4.38 ( pKa of ibuprofen) and 40% ACN at pH 6.72 and 30%ACN at pH 6.5 (above the pKa of ibuprofen) were used.

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