Estimation of binding constants for diclofenac sodium and bovine serum albumin by affinity capillary electrophoresis and fluorescence spectroscopy

Both affinity capillary electrophoresis (ACE) and fluorescence spectroscopy were used to measure the binding affinities between diclofenac sodium (DFS) and bovine serum albumin (BSA) in this investigation. In ACE, DFS was injected into the borate buffer containing various concentrations of BSA. Mobility ratio (M) was used to deduce the binding constant (K(b)), which effectively eliminates the effect of electroosmotic flow (EOF). Both ACE and fluorescence measurements indicated two classes of binding sites between DFS and BSA. The Kb value for high affinity binding sites (1.9 +/- 0.2 10(5) M(-1)) obtained from ACE is in agreement with that from fluorescence spectroscopy (2.8 +/- 0.3 10(5) M(-1)). The work demonstrates that ACE and fluorescence spectroscopy are complementary to each other for the determination of binding constants of DFS and BSA.