Spectrophotometric determination of some selected analgesic drugs based on complex formation reactions

Abstract

Accurate and precise spectrophotometric methods for the determination of four analgesic drugs namely, tramadol (TRM), morphine (MRF), nalbuphine (NLB) and naltrexone (NLT) in pharmaceutical formulations and biological fluids were developed and optimized. The proposed methods involve the addition of a measured excess of bromate-bromide mixture in acid medium and subsequent estimation of the residual bromine by reacting with a measured excess of iron (II), the remaining iron (II) is complexed with 1, 10-phenanthroline (method A) or with 2, 2' bipyridyl (method B) and measuring the increase in absorbance at 510 and 522 nm, respectively. In both methods, the amount of bromine reacted corresponds to the amount of drugs. The calibration graphs are found to be linear over 2.4 – 14.4 μg ml−1 and 1.6 – 12.8 μg ml−1 for method A and method B, respectively. Under the optimum conditions, Beer’s law limit, molar absorptivities and Sandell’s sensitivity are calculated. The limits of detection and quantification are 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 and biological fluids. No interference was observed from common additives and the validity of the methods was tested.