Determination of the binding constant of indomethacin-β-cyclodextrin complex by capillary electrophoresis:: experimental optimization and temperature study

The apparent electrophoretic mobilities of indomethacin in beta-cyclodextrin at a range of concentrations were measured directly by capillary electrophoresis. Three different linear plots and a non linear plot are proposed for the apparent binding constant calculations, based on the fact that the molar ratio of the inclusion complex was 1:1. K values obtained at 298 K were 421 M-1 (double reciprocal fit), 488 M-1 (x-reciprocal fit), 428 M-1 (y-reciprocal fit) and 490 M-1 (non linear fit). The corresponding K values at 313 K were 380 M-1 (double reciprocal fit), 355 M-1 (x-reciprocal fit), 366 M-1 (y-reciprocal fit) and 339 M-1 (non linear fit). Using the proposed methods, the binding constant of the indomethacin beta-cyclodextrin inclusion complex can be obtained easily. The methods have been applied to obtain the values of the constant K under different experimental conditions. Under optimized conditions the K constant is temperature dependent and non-arrhenian behaviour was observed.