Potentiometric Determination of Acid Dissociation Constants (pKa) for Human and Veterinary Antibiotics
Document Type
Article
Journal/Book Title/Conference
Water Research
Volume
38
Publication Date
2004
First Page
2874
Last Page
2890
Abstract
This work determined the acid dissociation constants (pKa) of 26 common human and veterinary antibiotics by potentiometric titration. Selected antibiotics consisted of sulfonamides, macrolides, tetracyclines, fluoroquinolones, and other miscellaneous antibiotics. After validation of analysis methods using phosphoric acid as a model compound, a second-derivative (Δ2pH/ΔV2) method was primarily applied to determining pKa's from titration curves for most antibiotics due to its convenience and accuracy. For tetracyclines, however, a least-square non-linear regression method was developed to determine their pKa's because the second-derivative method cannot well distinguish the pKa,2 and pKa,3 of tetracyclines. Results indicate that the pKa values are approximately 2 and 5–7.5 for sulfonamides; 7.5–9 for macrolides; 3–4, 7–8 and 9–10 for tetracyclines; 3–4, 6, 7.5–9 and 10–11 for fluoroquinolones; while compound-specific for other miscellaneous antibiotics. The moieties corresponding to specific pKa's were identified based on chemical structures of antibiotics. In addition, the pKa's available in literature determined by various techniques are compiled in comparison with the values of this work. These results are expected to essentially facilitate the research on occurrence, fate and effects, analysis methods development, and control of antibiotics in various treatment operations.
Recommended Citation
Qiang, Z., Adams, C. (2004) “Potentiometric Determination of Acid Dissociation Constants (pKa) for Human and Veterinary Antibiotics,” Water Research, 38, 2874-2890.
