Spectrophotometric Determination of Ampicillin by Ternary Complex Formation with 1, 10-phenanthroline and Copper (II)

A simple and convenient spectrophotometric procedure is described for the determination of ampicillin. The method is based on the formation of a yellow ternary complex with 1,10-phenanthroline and copper(II) in acetate buffer solution (pH ≍ 5.0) and measurement at 446 nm. The stoichiometry and stability constant of the ternary complex were determined. Beer′s law is obeyed in the concentration range 2.5-100 μg cm−3. The optimum concentration range evaluated by Ringbom′s method, the molar absorptivity, and the Sandell sensitivity of the ternary complex were determined. A variety of pharmaceutical dosage forms containing ampicillin were successfully analyzed by the proposed procedure, giving a relative standard deviation of 1.0%. Comparison of results with those of an official method shows good agreement and indicates no significant difference in the precision of the two methods.