الفهرس 
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Abstract
New two simple and accurate spectrophotometric methods have been developed for the determination of acetylcholinesterase inhibitor drugs (donepezil HCl (DNP) and rivastigmine tartrate (RVS)) and a serotonin 5-HT3 receptor antagonist (ondansetron HCl (OND) in pure forms and pharmaceutical formulations. The first method is based on the formation of yellow colored ion-pair complex between the basic nitrogen of the drugs (DNP, RVS or OND) and acid dyes, namely; bromocresol green (BCG), bromocresol purple (BCP), bromophenol blue (BPB) and bromothymol blue (BTB) in acidic buffer of pH range (3.0-4.0). The ion-pair complexes of DNP with BCG, BTB, BPB and BCP show maximum absorbances at 420, 413, 415 and 409 nm, respectively. The ion-pair complexes of RVS with BCG, BTB, BPB and BCP show maximum absorbances at 422, 415, 414 and 410 nm, respectively. The ion-pair complexes of OND with BCP and BPB show maximum absorbances at 408 and 413 nm, respectively. Beer’s law is obeyed in the concentration ranges 1.0-12,1.0-16 and 1.0-20 μg mL-1for DNP, RVS and OND, respectively. The correlation coefficient was ≥ 0.9993 with a relative standard deviation (R.S.D.) of ≤ 1.26. The second method, we investigate the development of indirect redox spectrophotometric reaction for determination of DNP, RVS or OND with N-bromosuccinimide (NBS) in acid medium, followed by determination of unreacted NBS by reacting it with a fixed amount of indigocarmine and measuring the absorbance at 610 nm (method A); amaranth and measuring the absorbance at 518 nm (method B) or methylene blue and measuring the absorbance at 664 nm (method C). In all three methods, the amount of NBS reacted corresponds to the amount of drug and the measured absorbance is found to increase linearly with the concentration of drug with correlation coefficients of 0.9994- 0.9999. Beer’s law is obeyed in the concentration ranges 0.2-5.0, 0.2-6.0 and 0.2-5.0 μg mL-1 for DNP, RVS and OND, respectively. The limits of detection and quantification are also reported. Intra-day and inter-day precision and accuracy of the methods have been evaluated. The proposed methods were successfully applied to determine the studied drugs in their formulations without any evidence for interference from pharmaceutical additives and the results were statistically compared with those of the reference methods by applying Student’s t-test and F-test. The accuracy of the methods was further ascertained by performing recovery studies via standard-addition method. The proposed methods can be confidently applied for quality control and routine analysis of the studied drugs.