A modified RP-HPLC method for the determination of the pK(a) values of synthesized beta-hydroxy-beta-arylalkanoic acids
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The pK(a) values of twelve beta-hydroxy-beta-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 (s)(w)pK(a) of a compound. Using (s)(w)pKa in previously established equations for the specific methanol/buffer mixture, the (w)(w)pK(a) values (in pure water) were calculated. The obtained wwpKa values for the synthesized compounds were in a range from 3.40 to 3.74, and the (w)(w)pK(a) for ibuprofen was 4.27. The Predicted pK(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 pK(a) values were calculated as a wide range.
Keywords:dissociation constant / anti-inflammatory compounds / ibuprofen / liquid chromatography / carboxylic acids
Source:Journal of the Serbian Chemical Society, 2018, 83, 7-8, 875-883
- Srpsko hemijsko društvo, Beograd