This paper aims to develop a simple, sensitive and accurate spectrophotometric method for quantitative determination of paracetamol in aqueous medium. The method is based on the reaction between the hydrolyzed paracetamol and 9-chloroacridine reagent (9-CA). The spectra of the product show maximum absorption at 436 nm. Beer's law is obeyed in the concentration range of 0.25-11 µg/mL with molar absorptivity value 5.3x103 L/mol/cm. The average recovery percentage (Rec%) is 99.27% and relative standard deviation (RSD) is :: 2.82%. In addition, the stability constant has been determined and the reaction mechanism is proposed. The method has been applied successfully for the assay of paracetamol in pharmaceutical formulations. It is found that the method does not require extraction process and it agree well with British pharmacopeia.  

Two sensitive methods have been proposed for spectrophotometric determination pure form of Doxycycline (Dox) and pharmaceutical preparation as capsule. The procedures based on the oxidation of the Doxycycline in acidic media by Fe(III). The results Fe(II) reacted with 1,10-phenanthroline in Method A, and the ferroin complex can measure at 510 nm versus the blank of reagent. While method B depends on the reaction of 2,2'-bipyridyl with the resulted Fe(II) to form a stable coloured complex with maximum 522 nm absorption against reagent blank. Beer's law is applicable in the range of 0.1-9.00 μg/ml and 0.15-4.50 μg/ml concentration with molar absorptivity values of 8.25×10 4 and 7.53×10 4 l.mol -1 .cm -1 for method A and B, respectively. For both processes, the mean percentage of recoveries is 99.9 % and 98.5% respectively. The suggested methods are free from interferences from common excipients. The proposed methods compared favorably with the official and other spectrophotometric methods.