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The p K a values of twelve β -hydroxy- β -arylalkanoic acids and ibupro­fen were determined using a modified RP-HPLC method. The stationary phase was octadecyl modified (C-18) silica gel, and the mobile phases were mixtures of methanol and one of ten different buffers (60:40 volume ratio). The mean retention time of each compound was plotted against the pH of each of the ten used mobile phases. The inflection point of the obtained sigmoidal curve repre­sents the  of a compound. Using in previously established equat­ions for the specific methanol/buffer mixture, the values (in pure water) were calculated. The obtained values for the synthesized compounds were in a range from 3.40 to 3.74, and the for ibuprofen was 4.27. The Predicted p K a values for this type of compounds in the MarvinSketch 5.11.5. Program were in poor correlation with the experimental results, while in ACD/ /I-Labs p K a values were calculated as a wide range.

A modified RP-HPLC method for the determination of the pKa values of synthesized β-hydroxy-β-arylalkanoic acids