Spectrophotometric determination of some analgesic drugs in pharmaceutical formulations using N-bromosuccinimide as an oxidant

New sensitive and rapid spectrophotometric methods for the determination of four analgesic drugs namely, nalbuphine (NALB), naltrexone (NALT), morphine (MORF) and tramadol (TRAM) in pharmaceutical formulations were developed and optimized. The proposed methods involve the addition of a measured excess of N-bromosuccinimide in acid medium followed by determination of unreacted NBS by reacting with either a fixed amount of methyl orange and measuring the absorbance at 508 nm (Method A), or orange G and measuring the absorbance at 478 nm (Method B). In both methods, the amount of NBS reacted corresponds to the amount of drugs. Under the optimum conditions, Beer’s law limit, molar absorptivity and Sandell’s sensitivity were calculated. The limits of detection and quantification were also reported for both methods. Statistical evaluation of the methods was examined by determining intra-day and inter-day precisions. The methods were successfully applied to the assay of drugs in their pharmaceutical formulations. No interference was observed from common additives and the validity of the methods was tested.