A simple spectrophotometric method is described for the determination of acetylcysteine (I) and captopril (II) as representative examples of thiols , as well as amlodipine besylate (III) and heptaminol hydrochloride (IV) as amine examples. The method is based on the reaction of these drugs with the activated halide 2,4-dinitrofluorobenzene (DNFB) in aqueous borate buffer to yield yellow colored products. Beer’s law was obeyed over the concentration ranges of 4-12, 2.4-16.8, 8-28 and 5-25 μg mL-1 for (I), (II), (III), and (IV), respectively. The different experimental parameters were studied and optimized. The proposed method was validated according to the USP 27 criteria and was found suitable for the quantitation of the cited compounds in their pharmaceutical preparations without interference from common excipients.