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).