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Simple, sensitive and rapid spectrophotometric techniques have been established for the determination of cimetidine (I), famotidine (II) and ranitidine hydrochloride (III) in presence of their S-oxide derivatives in both raw materials and in pharmaceutical formulations. Hydrogen peroxide was used to enhance the formation of S-oxide compounds (oxidative derivatives). The first derivative of the ratio spectra ( 1 DD) technique has been applied for the determination of (I) and (II). While, direct zero order ( 0 D), first derivative ( 1 D) and the second derivative of the ratio spectra ( 2 DD) have been carried out for the determination of drug (III). Linear calibration 1055 curves were obtained for determination of (I) and (II) by applying 1 DD at 220 and 230 nm in the concentration range of 2-20 and 4-40 mg mL À1 with the mean percentage recoveries of 99.88 AE 0.943 (n ¼ 10) and 99.88 AE 0.824% (n ¼ 10) for (I) and (II), respectively. While for (III) linear calibration curves were obtained by applying 0 D, 1 D and 2 DD at 313, 334 and 255 nm, respectively. The concentration range was 2-20 mg mL À1 with the corresponding mean percentage recoveries of 100.13 AE 0.464, 100.01 AE 0.428 and 99.94 AE 0.439 for (I), (II) and (III), respectively. The results obtained by the proposed methods were statistically analyzed and compared with those obtained by the official BP methods.

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The interaction between 7,7',8,8'-tetracyanoquinodimethane (TCNQ) and oxamniquine (I), azithromycin (II), omeprazole (III), pantoprazole (IV), and benzydamine hydrochloride (V) was investigated. The reaction conditions were optimized to obtain typical charge transfer complexes (CTC). The nature of the formed complexes was proved by thorough study of the thermodynamic parameters namely delta G (free energy), delta H (enthalpy), and delta S (entropy). The association constant KcAD and the molar absorptivity xi lambda AD of the formed complexes were determined using the Benesi-Hildbrand equation. The effect of temperature on these constants gave evidence of CTC formation. The reaction of TCNQ with I-V was found to be in 1:1; as being determined by the Foster method. Spectrophotometric measurements of the formed CTC were used for the quantitative determination of the studied drugs in both pure or pharmaceutical formulation. The mean percentage recoveries were 99.17 +/- 0.34, 99.75 +/- 0.12, 100.52 +/- 0.41, 98.75 +/- 0.63, and 99.23 +/- 62 for I, II, III, IV, and V, respectively. There was no significant difference observed when the method was statistically compared with the official and reference methods used to determine these drugs.