Spectrophotometric determination of ampicillin sodium in pharmaceutical products using sodium 1,2-naphthoquinone-4-sulfonic as the chromogentic reagent

Spectrophotometric determination of ampicillin sodium is described. The ampicillin sodium reacts with sodium 1,2-naphthoquinone-4-sulfonic in pH 9.00 buffer solution to form a salmon pink compound, and its maximum absorption wavelength is at 463 nm, epsilon463 = 1.14 x 10(4). The absorbance of ampicillin sodium from 2.0-80 microg ml(-1) obeys Beer's law. The linear regression equation of the calibration graph is C = 40.24A - 2.603, with a linear regression correlation coefficient is 0.9997, the detection limit is 1.5 microg ml(-1), recovery is from 97.23 to 104.5%. Effects of pH, surfactant, organic solvents, and foreign ions on the determination of ampicillin sodium have been examined. This method is rapid and simple, and can be used for the determination of ampicillin sodium in the injection solution of ampicillin sodium. The results obtained by this method agreed with those by the official method (HPLC).