Surfactant-to-Dye Binding Degree Method for the Determination of Morphine Hydrochloride and Codeine Phosphate in Pharmaceuticals

Abstract

The surfactant-to-dye binding degree method was used to determine morphine hydrochloride and codeine phosphate. Neutral red and bis(2-ethylhexyl) sulfosuccinate (AOT) were used as the dye and surfactant, respectively, to form dye–surfactant aggregates. Addition of the drug resulted in a decrease in the dye–surfactant binding degree, proportional to the drug concentration. This was measured by monitoring the absorbance changes of the dye at 532 nm. Under the optimum conditions, the calibration graphs were linear up to 32 and 28 µg mL−1 for morphine hydrochloride and codeine phosphate, respectively, with the corresponding detection limits of 0.40 and 0.35 µg mL−1.