9. Spectrophotometric and spectrofluorimetric determination of amlodipine besilate and doxazosin mesilate in bulk and in dosage forms via Hantzsch reaction

Simple, accurate, and sensitive spectrophotometric and spectrofluorimetric methods for analysis of amlodipine besilate and doxazosin mesilate were developed and validated. Acetylacetone together with formaldehyde react with primary amines by Hantzsch reaction forming a yellow product (dihydrolutidine derivatives) that can be measured either spectrophotometrically or spectrofluorimetrically. Different variables affecting the reactions conditions were carefully studied and optimized. Under the optimum conditions, Beer's law was obeyed in the concentration range of 6-44μg/mL for amlodipine besilate and 8-36μg/mL for doxazosin mesilate, using spectrophotometric method. For the case of spectrofluorimetric method, Beer's law was obeyed in the concentration range of 1.6-7.6μg/mL and 0.02-0.22μg/mL for amlodipine besilate and doxazosin methylate, respectively. The precision of the methods were satisfactory; the values of relative standard deviation did not exceed 2%. The reaction stoichiometry was studied and the proposed methods were successfully applied for the analysis of the investigated drugs in pure and pharmaceutical dosages forms. The results obtained by the proposed methods were comparable with those obtained by the reference method.