Nonsteroidal Anti-Inflammatory Drugs Ion Mobility: A Conductometric Study of Salicylate, Naproxen, Diclofenac and Ibuprofen Dilute Aqueous Solutions

The electric conductivities of aqueous solutions of nonsteroidal anti-inflammatory drugs salicylate, naproxen, ibuprofen sodium and diclofenac sodium salts and diclofenac potassium salt were measured in the temperature range from 278.15 K to 313.15 K (in steps of 5 K) and in the concentration range 3 × 10–4 < c(mol/dm–3) < 0.007. Data analysis based on the low concentration chemical model of electrolyte solutions yielded the limiting molar conductivity, A∞,and the association constant, KA. Using the known data of the limiting conductivities of sodium and potassium ions the limiting conductivities of the salicylate, naproxen, diclofenac and ibuprofen anions were evaluated, and the radii of anions in water were estimated. Total dissociation of the investigated salts in water is evident and the considerable differences in the anion mobilities are observed. They are discussed in terms of possible hydration and hydrophobic interactions.