Chemical Determination of Folic Acid in the Presence of p-Aminobenzoic Acid or Procaine Hydrochloride

The USP XVII chemical method for the determination of folic acid is not applicable to pharmaceutical preparations containing p-aminobenzoic acid (PABA) or procaine hydrochloride (added to intertables to reduce discomfort). PABA is often present in older folic acid injectables in which a breakdown of the folic acid has occurred on long standing. A modified method is described to eliminate interference from these compounds by diazotizing the interfering material and then converting it to the corresponding phenol. The folic acid is then cleaved to form PABA, diazotized, and coupled with the Bratton-Marshall reagent. In a comparison of the two methods using known amounts of folic acid in the presence of PABA, better recovery of folic acid was achieved with the modified method than with the USP method. The application of this modification to commercial preparations is also demonstrated.