Indirect Spectrophotometric Determination of PABA in Pharmaceutical Preparation(capsules)


Abstract An indirect spectrophotometric method is developed for the determination of p-aminobenzoic acid (PABA) is developed for the determination of PABA as pure and in pharmaceutical preparations. The method is based on the oxidation of PABA with iron(III) in acidic medium, then reaction of iron(II) with 1,10-phenathroline to produce a red complex which is water-soluble, stable and has a maximum absorption at 510 nm against the reagent blank with a molar absorptivity of 4.93×104 L.mol-1 .cm-1 . The variables affecting the intensity of complex have been studied and optimized. Under the optimum conditions, the calibration graph is linear over the range 5-80 µg /25 ml (0.2-3.2 ppm), with a relative error of -0.41 to -0.09 and a relative standard deviation of ±0.060 to ±0.507 depending on concentration level. The proposed method is applied to determine PABA in pharmaceutical preparation (capsules).