T HE batch adsorption of doxycycline from aqueous solution using aluminum oxide under different experimental conditions was investigated in this study. The effect of initial concentration, sample volume, contact time and pH have been reported. A comparison of kinetic models applied to the adsorption of doxycycline on the adsorbents was evaluated for the pseudo first-order, the pseudo-second-order, Elovich, Fractional power and intra particle diffusion kinetic models were utilized to the adsorption data in respect of investigating the kinetic process; kinetic data were best fitted to the pseudo-second-order model validated by normalized standard deviation (NSD), average relative error (ARE) and chi-square test (Chi-X2). The result suggested that the intra particle diffusion was one of the rate-limiting steps.

A sensitive spectrophotometric method has been developed for the determination of Doxycycline hyclate (DCH) as pure and capsule forms. This method is based on diazotization of primary amine group of benzocaine with sodium nitrite in hydrochloric acid medium; the formed diazonium salt is then reacted with DCH in sodium hydroxide medium, to form yellow orange Azo dye. Beer's law is obeyed in the concentration rang 16-34mg. ml -1 at 480 nm with detection limit LOD and molar -1 and 2.214× 10 +4 L.mol -1 .cm -1 , respectively.

Three rapid, accurate and ecological friendly spectrophotometric methods are used for determination of Vancomycin at wavelength 200 nm for the zero-order method, 195-205 nm for the area under the curve (AUC) method and 200 nm for the first derivative method(D1). A calibration graph shows that Beer's law is obeyed over the concentration range between 4-16 mg.L-1 for all three methods with a correlation coefficient of 0.994, 0.998 and 0.997 for zero-order, AUC and D1 at valley 200 nm, respectively. Average of Rec.% were found to be of 100.870, 101.425 and 99.515 for zero-order, AUC and D1 at valley 200 nm, respectively. Statistical analysis of data reveals that all three methods are precise, accurate and suitable for the application Vancomycin in pure and pharmaceutical preparations.

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