Methyl acetoacetate as a Coupling Agent inSpectrophotometric Determination of p- Aminobenzoic Acid by Azo-Dye Formation Reaction

A simple spectrophotometric method for the determination of paminobenzoic acid (PABA) in aqueous solution. The method is based on the reaction of PABA, with excess nitrite, in an acidic medium, to produce the corresponding diazonium salt. After the removal of residual nitrite with sulfamic acid, the diazonium salt is coupled with methyl acetoacetate reagent in basic medium to produce, an intense yellow coloured water-soluble and stable azo-dye which exhibits maximum absorption at 365nm. Beer’s law is obeyed over the range 10-260μg of PABA in final volume of 25 ml i.e., 0.4-10.4 ppm with a molar absorptivity of 2.41×10^4 l.mol^-1.cm^-1 and Sandell sensitivity index of 0.0056μg.cm-2, a relative error of –0.70 to +0.43% and relative standard deviation of ±0.13 to ±1.01% depending on the concentration level. The method has been applied to the determination of PABA result from degradation of procaine-penicillin injection and from tablets of folic acid.