Simple determination of deoxycholic and ursodeoxycholic acids by phenolphthalein-beta-cyclodextrin inclusion complex.

An expeditious colorimetric methodology for the determination of the deoxycholic acid (DCA) and of the ursodeoxycholic acid (UDCA) in pharmaceutical formulations is reported. The method is based on their competitive complexation reaction with a color indicator to form beta-cyclodextrin-inclusion complexes. Several pH color indicators were tested, but phenolphthalein (PHP) showed the best interaction with the beta-cyclodextrin (beta-CD) with an inclusion yield higher than 95%. The best concentrations of beta-cyclodextrin to form inclusion complexes were 1.24 x 10(-3) and 6.2 x 10(-4) M at pH 9.5 and 10.5. Statistical analysis of the results showed that the pH had a significant effect on the DCA determination and that high beta-CD-PHP inclusion complex concentrations had a significant negative effect on the UDCA determination (p < 0.05). The limit of detection and limit of quantification were 3.94 x 10(-5) and 1.31 x 10(-4) M for DCA (range: 6.1 x 10(-6)-3.13 x 10(-3) M), 4.08 x 10(-5) and 1.36 x 10(-4) M for UDCA (range: 6.05 x 10(-6)-3.88 x 10(-4) M). This simple and cheap method showed high stability and feasible instrumentation.