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.

A novel study describes the development and validation of a selective and simple kinetic spectrophotometric method for the determination of some analgesic drugs namely, morphine (MOF), nalbuphine (NAB) and naltrexone (NAT) in bulk and in pharmaceutical formulations. This method was based on the reaction of the drugs under studying with alkaline KMnO 4 to form a water-soluble bluish green colored product with a maximum absorbance at 605 nm. Although, the determination of MOF, NAB and NAT drugs by rate constant, fixed-concentration and fixed time methods were feasible with the calibration equations obtained, the fixed time method has been found to be more applicable. The fixed-time method is adopted for constructing the calibration curves, which were found to be linear over the concentration ranges of 4 -18 mg mL -1 MOF, 2 -20 mg mL -1 NAB and 2 -16 mg mL -1 NAT. Different experimental parameters which can affect the development and stability of the color were carefully studied and optimized. The fixed time method of 20 min was further applied to pharmaceutical formulations of each drug and the percentage recoveries were 99.85±0.049 to 102.27±0.024. Statistical comparisons of the results with the reference methods show the excellent agreement and indicate no significant difference in accuracy and precision.

A simple, rapid, accurate, precise and sensitive spectrophotometric method for the determination of four analgesic drugs namely, tramadol (TRAM), morphine (MORF), nalbuphine (NALB) and naltrexone (NALT) in bulk sample and in dosage forms is described. The method is based on oxidation of the studied drugs by potassium permanganate in acidic medium and determination of the unreacted oxidant by measuring the decrease in the absorbance of indigo carmine (IC) dye at 610 nm. 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. Statistical evaluation of the method was examined by determining an intra-day and inter-day precisions. The method was successfully applied to the assay of drugs in their pharmaceutical formulations. No interference was observed from common additives and the validity of the method was tested.

Objective: To develop and validate simple, rapid and sensitive spectrophotometric method for the assay of four antimuscarinic antagonists, namely oxybutynin (OXB), solifenacin (SOL), tolterodine (TOL) and fesoterodine (FES) in bulk and pharmaceutical formulations.Methods: The proposed method is based on the reaction of the selected drugs with eriochrome cyanine R (ECR) in buffered aqueous solution at pH 1.0. The formed ion-pair complexes were extracted with dichloromethane and measured quantitatively with maximum absorption at 464 nm. All variables that affect on color intensity such as pH, buffer volume and concentration of ECR and extractive solvents were studied and optimized.Results: The calibration graphs were linear over the concentration range of 4–24, 4–32, 4–32 and 2–22 mg/ml for OXB, SOL, TOL and FES, respectively. The stoichiometry of the reaction was found to be 1:1 in all cases. Molar absorptivity values were found to be 2.043×104, 1.856×104, 1.798×104 and 2.856×104 l/mol/cm for OXB, SOL, TOL and FES, respectively. Excipients which used as an additive in commercial formulations did not interfere in the analysis.Conclusion: The developed method was successfully applied to determine OXB, SOL, TOL and FES in pharmaceutical preparations. The developed method can be used for quality control and routine analysis where time, cost effectiveness and high specificity of analytical technique are of great importance.

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