The suggested work included simple accurate diazo-coupling spectrophotometric method for the determination of phenylephrine-HCl (PHEPH) in pure drug and tablet formulation. The method was based on coupling of PHEPH with diazotized 2,4-dinitroaniline in alkaline medium. The sensitivity expressed by the value of molar absorptivity of yellowish-orange azo-dye was 1.915 ×10 4 L. mol-1. cm-1 , the maximum absorption at 455 nm and Beer's law obeyed within the range of 10-200 μg/10ml of PHEPH. The color of the product was highly stable and did not show a significant change in absorbance up to 60 min. with a recovery of 99.97% and a RSD% is 0.024%. The PHEPH in nose drop and syrup has been estimated with satisfactory results.
A simple and sensitive indirect spectrophotometric method was developed for the determination of folic acid in pure form and in its pharmaceutical formulations. The method was based on the oxidation of folic acid by iron (III) in acidic medium, then reaction of liberated iron (II) with 2, 2'-bipyridyl to produce a red complex which is water-soluble, stable, and has a maximum absorption at 520 nm against the reagent blank with a molar absorptivity of 2.8338 x 105 L .mol-1.cm-1. Beer’s law is valid over the concentration range of 0.5-18.0 µg/ml folic acid. The values of some thermodynamic parameters [free energy change (∆G), enthalpy change (∆H), and entropy change (∆S)] were estimated from the values of stability constants (K) at different temperatures .It was found that colored product formation was spontaneous, exothermic and accompanied by an increase of random. The proposed method has been applied successfully to determine folic acid in different pharmaceutical preparations.
Three simple, accurate and precise spectrophotometric methods were proposed for determining of mefenamic acid in pure form as well as in dosage forms. The proposed methods were based on the coupling of mefenamic acid with diazotized 4-aminohippuric acid, 4-nitroaniline and 4-aminoantipyrine in alkaline medium for methods A, B and C, respectively. The colored azo dyes were quantitated photometrically at 432, 453, and 406 nm for methods A, B and C, respectively. Different variables affecting the reactions were optimized. Beer’s law was obeyed over the concentration ranges of 0.5-20, 1.0-16 and 0.2-14 μg/ml for methods A, B, and C, respectively. The colored azo dyes remained stable for more than 3 hours in the three methods. The proposed methods were applied successfully to determine mefenamic acid in dosage forms.
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