Determination of Trimethoprim Based on Charge-Transfer Complexes Formation

A spectrophotometric study concerning the interaction between trimethoprim (tmp) ,sulfamethoxazole (sfmx), as n-donor and 2,3-dichloro-5,6- dicyano-p-benzoquinine (ddq) and chloranilic acid (ca) as π-acceptor were been performed at 25°c. the results of interaction of ca and ddqwith tmp indicate the formation of a 1:1, 1:2, charge transfer complexes through non equilibrium reactions. in the case of sfmx, the formation of 1:2 (sfmx/ddq, sfmx /ca) charge-transfer complexes is confirmed. the formation constants of the equilibrium step were evaluated from the computer fitting of the absorbance-mole ratio data. also, this study was carried out to simultaneously determine quantitatively tmp in cotrimoxazole. the complexes of tmp with ddq and chloranilic acid absorbed maximally in 512 and 585, respectively.