抄録
Ion pair extraction of a basic drug (trimethoprim) with sulfonphthaleins (BTB, BCG and BPB) was examined on the basis of equation (1). [numerical formula] The molar ratio, Q, of the extracted ion pair (Q=[BH+IH-]org/(CB-[BH+IH-]org)) was represented as a function of the hydrogen ion activity ((αH)W) and the concentration of the sulfonphthalein monoanion ([IH-]W). The extraction constant, Kex, of the equilibrium (2) was estimated from equation (1). [numerical formula] The log Kex values of TMP-BTB were found to be 5.26, 7.08 and 8.10 in benzene-H2O, 1, 2-dichloroethane-H2O and CHCl3-H2O systems, respectively. The log Kex values of TMP-BCG and TMP-BPB in the 1, 2-dichloroethane-H2O system were found to be 5.89 and 4.95, respectively. The effect of pH on the ion pair extraction is discussed in terms of equation (1). The pH values suitable for the assay of TMP with BTB by means of ion pair extraction were found to be in the range of 4 to 6.
