Spectrophotometric determination of dapsone in pharmaceutical products using sodium 1,2-naphthoquinone-4-sulfonic as the chromogenic reagent.

Spectrophotometric determination of dapsone is described. The dapsone reacts with sodium 1,2-naphthoquinone-4-sulfonic in pH 6.98 buffer solution to form a salmon pink compound, and its maximum absorption wavelength is at 525 nm, epsilon525=3.68 x 10(4) l mol(-1) cm(-1). The absorbance of dapsone from 0.40 to 10 microg ml(-1) obeys Beer's law. The linear regression equation of the calibration graph is C=0.2334 A + 0.01288, with a linear regression correlation coefficient of 0.9998, the detection limit is 0.24 microg ml(-1), and recovery is from 99.2 to 102.4%. Effects of pH, surfactant, organic solvents, foreign ions, and standing time on the determination of dapsone have been examined. This method is simple and can be used for the determination of dapsone in injection solution of dapsone. The results obtained by this method agreed with those by the official method (dead-stop titration method [The Chinese Pharmacopoeia, Pharmacopoeia Commission, Ministry of Health, vol. 2, fifth ed., PRC Chemical Industry Press, Beijing, 2000, p.720]).